Cheese making can be described as the process of removing water, lactose and some minerals from milk to produce a concentrate of milk fat and protein. The essential ingredients of cheese are milk, coagulating enzyme (rennet), bacterial cultures and salt. Rennet causes the milk proteins to aggregate and ultimately transform fluid milk to a semi-firm gel. When this gel is cut into small pieces (curds), the whey (mostly water and lactose) begins to separate from the curds. Acid production by bacterial cultures is essential to aid expulsion of whey from the curd and largely determines the final cheese moisture, flavour and texture. A flow chart showing the general operations of cheese making is in Figure 1.1.

Figure 1.1 Flowchart of Cheese Making Process.

The objectives of cheese making are: (1) To obtain the optimum cheese composition with respect to moisture, acidity (pH), fat, protein and minerals (especially calcium); (2) Establish the correct structure of the cheese at the microscopic level; and (3) Ripen to perfection. Objectives (1) and (2) are achieved by varying initial make procedures and it is then possible to achieve objective (3). Most of these variations in initial make procedures are different means to control the rate and extent of acid development, and the rate and extent of moisture release. Grouped according to texture and basic manufacturing procedures, seven cheese families are described below and summarized in Table 1.1. Table 1.2 contains composition data for some common cheese varieties.

 

Table 1.1: Some properties of cheese categorized according to type of coagulation and procedures used for pH and moisture control. Adapted from Hill (2007). Plus signs in column three indicate relative amounts.

The cheese families described above provide a useful 'coat rack' to help organize cheese according to the initial manufacturing procedures which determine cheese composition and its primary micro-structure. The following is a more comprehensive summary of technological parameters which determine cheese characteristics.

• Species: cow, goat, sheep, buffalo, yak, other
• Milk standardization
  • Fat and protein contents
  • Whey and milk blends
• Coagulation
  • rennet gel
  • acid gel
  • heat-acid precipitate
• Moisture control
  • Cooking temperature and time
  • Mesophilic versus thermophilic cultures
  • Amount and acidifying properties of the culture
  • Heat treatment of the milk
• Type of pH control
  • Direct acidification vs fermentation
  • Amount and type of culture
  • Lactose removal:
    • Washing (American, Dutch)
    • High temperature syneresis (Swiss, Hard Italian)
    • High acid syneresis (Feta, Cheshire)
    • Cheddaring (Cheddar, Pasta Filata)
• Extent of acid development
  • Low acid (minimum pH > 5.8), Latin American fresh cheese
  • Medium acid (minimum pH 4.9 - 5.5), most European varieties
  • High acid (minimum pH < 4.9), Fresh cheese, soft ripened cheese
• Salting procedures
  • Salt before forming
  • Surface salt after forming
  • Immersion in salt brine
• Type and duration of ripening
  • Fresh versus ripened
  • Interior, including blue veined cheese
  • Interior and surface ripened
    • Bacterial/yeast smears
    • White surface mould
• Type of rind
  • Rindless-waxed, film wrapped, painted
  • Dry rind (cured at 85% relative humidity)
  • Surface ripened (cured at 90-95% relative humidity)
• Texture
  • Openings: mechanical, small holes, large holes
  • Firmness
• Melting properties
  • No melt: softening without flow (frying cheese)
  • Stretching: Low melt and strongly elastic (Mozzarella)
  • Fondue: Medium melt, medium elasticity (Raclette)
  • High melt: flows readily with no stretch (aged Cheddar)

 

 Chemical Analysis

Depending on the size and shape, firm to hard cheese should be sampled using a cheese trier (at least 100 g sample) or by taking a sector sample. Soft cheese can be blended for sampling or sector sampled depending on its texture. Cheese samples are stored in opaque air tight containers and fragmented using a grater or other device before analysis. It is important to grind and mix the sample well before subsampling for analysis.

If the analytical procedure requires less than a 1 gm sample it is desirable to prepare a liquid cheese homogenate and a subsample from the homogenate. An homogenate suitable for most purposes can be prepared as follows.

• Weigh 40 g cheese into a blender container
• Add about 100 g of 7% sodium citrate solution
• Blend until homogenous (high speed blender such as Polytron is most suitable).
• Rinse blender shaft into container and make up to final weight of about 200g.

Note that cheese is notorious for inhomogeneous composition. Brine salted cheese have pronounced salt and moisture gradients, namely, higher salt and lower moisture near the surface. Large blocks or wheels of pressed cheese, will have moisture and pH gradients, namely, increasing moisture and decreasing pH towards the interior. In addition to moisture and salt gradients, surface ripened cheese also has pH gradients, namely, pH increases at the surface during curing. These difficulties greatly complicate the matter of obtaining accurate composition and mass balance (yield) data. A useful approach to improve yield control of large blocks is to set aside small blocks (eg., 20 kg blocks of Cheddar) for early composition and quality testing, and subsequently, conduct representative sampling of the large blocks (eg., 240 kg blocks of Cheddar) during the cut/wrap process.

Microbial Analysis

Obtain samples as described above for chemical analysis. Triers or knives used for sampling must be flame sterilized. Samples should be stored in sterile bags such as Whirl Pack bags, stored at 0-4C and analysed within 24 hours.

Equipment

1. Balance, 1,000 g capacity
2. Blender
3. Blender container autoclaved or sanitized with 200 ppm chlorine solution for 5 min.

Procedure

1. Break the cheese into small pieces while still in the bag. Use a pestle or similar device if necessary.
2. Heat dilution blanks of sterile aqueous 2% sodium citrate to 40C. Transfer 30 g of cheese to sterile blender container, add 270 ml diluent and mix for 2 min. at speed sufficient to emulsify the cheese properly. If temperature exceeds 40C during blending, use a shorter mixing time or decrease initial temperature of citrate solution. This 1:10 dilution should be plated or further diluted immediately.
3. Further dilutions can be prepared as required. Pipette 11 ml of the 10-1 dilution of the homogenate, avoiding foam, into 99 ml dilution blank (0.1% peptone) or 10 ml into 90 ml dilution blank. Shake this and all subsequent dilutions vigorously 25 times in a one foot arc. Prepare 10-1, 10-2, and 10-3 dilutions.

Oven Method

1. Pre-dry aluminum dishes (105C, 1 h) and weigh to the nearest 0.1 mg on an analytical balance.
2. Weigh quickly 3-5 g of fragmented cheese into the aluminum dish. The weight of sample is the total weight minus the weight of the dish from Step 1.
3. Dry to constant weight (about 16 h) at 105C. To check for constant weight: weigh at least two samples, return both samples to the oven for an additional 20 minutes, and re-weigh. The difference between the weights before and after the additional drying period should be less than 1 mg.
4. Cool in desiccator and determine total dry weight. Sample dry weight is the total dry weight less the weight of the dish determined in Step 1.
5. Report total solids and moisture contents on weight percent basis as follows:

Note: Several rapid moisture tests based on infrared or microwave drying are available. Check with your laboratory equipment supplier.

Application

Accurate cheese moisture analysis is critical to composition and yield control. Rapid moisture tests (e.g., microwave moisture oven) can be used to obtain early feed back (e.g., cheese moisture immediately after pressing) information to help with process control.

Principle

See discussion of pH and acidity in Section 3.5.

Apparatus and Reagents

1. An acidimeter equipped with a burette graduated in tenths of a ml up to 10 ml, and some means of filling the same without undue exposure of the solution to the carbon dioxide of the atmosphere.
2. N/10 sodium hydroxide solution.
3. A dropping bottle containing a 1% alcoholic phenolphthalein solution.
4. White cup, glass stirring rod, 17.6 ml pipette (or 8.8 or 9.0 ml pipette)
5. For cream, Torsion balance and 9 g weight.

Method

1. Mix sample thoroughly by pouring it from one container to another. The temperature of the sample should be near 20C.
2. Pipette 17.6 ml of milk or cream into a white cup. Note: 8.8 ml pipettes may also be used but are no longer as readily available as 17.6 ml pipettes. Readily available 9 ml pipettes are also used but require application of a correction factor to the final result.
3. Add six drops of phenolphthalein indicator solution to milk, 10 drops if the product is cream.
4. Titrate the sample with the N/10 sodium hydroxide solution (0.1 Normal NaOH) while stirring the sample with the glass rod. Look for the appearance of a faint pink colour which signals the endpoint. Add another drop or half a drop of NaOH if the pink colour does not persist for 30 s.
5. Record the number of ml of NaOH used to reach the endpoint. This value is called the 'titre'. Titratable acidity reported as percent lactic acid is dependent on the volume of sample.

For the 8.8 ml pipette, % Lactic acid = titre

For the 17.6 ml pipette, % Lactic acid = 0.5 x titre

For the 9.0 ml pipette, % Lactic acid = 0.98 x titre.

Note that there is practically no lactic acid in fresh milk, but it is a North American convention to report TA in terms of % lactic acid.

Application

As described in the next section, both titratable acidity (TA) and pH are measures of acidity. However, for most process control purposes, pH is a more useful measurement. Many cheese makers, however, still use TA to monitor initial acid development (that is to check for culture activity) during the first hour after adding the culture. For this purpose, TA is a more reliable indicator because relative to pH measurement, it is more sensitive to small changes in milk acidity.

When using TA to monitor initial culture activity note that:

1. You are looking for a measurable increase in TA to confirm that the culture is active. For example, if the initial TA taken immediately after the culture was added is 0.183% lactic acid, and the TA after one hour of ripening is 0.194 % lactic acid, the change in TA is 0.194 - 0.183 which is 0.011%.
2. Different people will interpret the coloured endpoint differently, so it is important that the same person takes both the initial and final TA measurements.
3. Carefully performed, it is possible to reliably measure a change in TA of 0.05% lactic acid, so if the TA increase is greater than 0.05% you can conclude that the culture is active. In most cases TA increases in the range of 0.05% to 0.10% are obtained after about 30 minutes of ripening (that is, 30 minutes after adding the culture).
4. It is critical to take the initial TA reading after the culture is added, because the culture (especially the bulk culture) is acidic.

Concepts of Acidity and pH

All aqueous systems (including the water in you and in cheese) obey the following relationship (Equation 3) between the concentration of hydrogen ions (H+) and hydroxyl ions (OH-). Note, the square brackets indicate concentration in moles per litre. A mole is 6 x 1023 molecules, that is, the numeral six with 23 zeros after it.

[H+] x [OH-] = 10-14

Because the actual concentrations in moles per litre are small, it is customary to express the values as exponents. For example, if we know that the concentration of hydrogen ions [H+] in a sample of milk is 0.000001 moles/l which is equivalent to 10-6 moles/l, we can calculate the concentration of hydroxyl ions as 10-14/10-6 = 10-8 moles/l which is the same as 0.00000001 moles/l.

• If [H+] = [OH-] the solution is neutral with respect to acidity.
• If [H+] > [OH-] the solution is acidic.
• If [H+] < [OH-] the solution is basic or alkaline.
• Chemicals which contribute H+ or absorb OH- are acids, while bases contribute OH- or absorb H+.

The concept of pH evolved as a short hand method to express acidity. We have already seen that a hydrogen ion concentration of 0.000001 moles/l can be expressed as [10-6], an expression which defines both the unit of measurement and the numerical value. The concept of pH is a further abbreviation which expresses the concentration of hydrogen ions as the negative log of the hydrogen ion concentration in units of moles/l. This sounds complex but is quite easy to apply. For example, the log10 of hydrogen ion concentration of [10-6] is equal to -6. The final step is to take the negative of the log, that is -1 x -6 which is 6. So, 0.0000001 moles/l = [10-6] = pH 6. From the relationship expressed in Equation 3, if the concentration of one of OH- and H+ is known, it is always possible to calculate the concentration of the other. So, if the pH of a solution is 6, the pOH is 14 - 6 = 8. Because this relationship is understood, the convention is to only report pH. Note, that because the negative sign was dropped by convention, decreasing pH values mean increasing acidity, that is, increasing concentration of H+ ions. So, although both TA and pH are measures of acidity, pH decreases with increasing acidity.

All of this can be summarized by a description of the pH scale. The pH scale for most practical purposes is from 1 to 14, although a pH of less than one is theoretically and practically possible.

pH 7.0 is neutral acidity [H+] = [OH-]

pH < 7.0 = acid condition [H+] > [OH-]

pH > 7.0 = alkaline condition [H+] < [OH-]

pH Versus Titratable Acidity

TA and pH are both measures of acidity but, for most purposes, pH is a better process control tool, because the pH probe measures only those H+ which are free in solution and undissociated with salts or proteins. This is important because it is free H+ which modifies protein functionality and contributes sour taste. It is also the pH rather than titratable acidity which is the best indicator of the preservation and safety effects of acidity. It must be emphasized, that the most important factor available to the cheese maker to control spoilage and pathogenic organisms is pH control. The pH history during and after cheese manufacture is the most important trouble shooting information. Cheese moisture, mineral content, texture and flavour are all influenced directly by the activity of free hydrogen ions (i.e. pH).

Titratable acidity (TA) measures all titratable H+ ions up to the phenolphthalein end point (pH 8.5) and, therefore, varies with changes in milk composition and properties. During cheese manufacture, the pH gives a true indication of acid development during the entire process so that the optimum pH at each step is independent of other variables such as milk protein content. However, the optimum TA at each step in cheese making will vary with initial milk composition and the type of standardization procedure used.

A good practical illustration of the difference between TA and pH is the effect of cutting. Up to the time of cutting, TA of the milk increases with the development of acidity by the culture. After cutting the TA of the whey is much lower. This does not mean that acid development stopped. It simply means that titratable H+ ions associated with the milk proteins are no longer present in the whey. This leads to the concept of buffer capacity, which is an important principle in cheese making. The effect of protein removal on the TA of whey, is related to the ability of protein to 'buffer' the milk against changes in pH. That same buffer property is the reason it helps to take acidic medication, like aspirin, with milk.

Buffer capacity can be described as the ability of an aqueous system, such as milk, to resist changes in pH with addition of acids (added H+) or bases (added OH-). Specifically, buffer capacity is the amount of acid or base required to induce a unit change in pH. For example, a small addition of acid to distilled water will cause a large reduction in pH. The same amount of acid would have a small effect on the pH of milk because milk proteins and salts neutralize the acidity.

The two most important buffer components of milk are caseins (buffer maximum near pH 4.6) and phosphate (buffer maxima near pH 7.0). The buffer maximum near pH 5.0 is extremely important to cheese manufacture because the optimum pH for most cheese is in the range of 5.0 - 5.2. As the pH of cheese is reduced towards pH 5.0 by lactic acid fermentation, the buffer capacity is increasing (i.e., each incremental decrease in pH requires more lactic acid). The effect is to give the cheese maker considerable room for variation in the rate and amount of acid production. Without milk's built in buffers it would be impossible to produce cheese in the optimum pH range.

Another way to illustrate the difference between TA and pH is to consider typical ranges of pH and TA for normal milk. TA is a measure of the total buffer capacity of milk for the pH range between the pH of milk and the phenolphthalein end point (about pH 8.3). The pH of milk at 25C, normally varies within a relatively narrow range of 6.5 to 6.7. The normal range for titratable acidity of herd milks is 0.12 to 0.18% lactic acid In other words, pH is a good indicator of initial milk quality, while the traditional measurement of TA to indicate bacterial growth in milk is less precise.

pH Measurement

The pH of cheese milk, whey and soft cheese can be measured directly. Firm and hard cheese must be fragmented before analysis. Always measure cheese pH in duplicate and use extreme care in handling the electrode. Place the fragmented cheese in a 30 ml vial or small beaker and gently push the electrode into the cheese ... too much haste is likely to break the electrode on the bottom of the beaker. To ensure good contact, press the cheese around the electrode with your fingers. There is no need to rinse the electrode between cheese samples. However, if the electrode is stored in buffer it should be rinsed with distilled water before measuring cheese pH. Always store the electrode in pH 4 buffer or as directed by the manufacturer. Do not rub the electrode. The electrode should be washed with detergent and rinsed with acetone occasionally to remove fat and protein deposits.

Apparatus and Materials

1. Babcock centrifuge.
2. Water bath at 55C.
3. Torsion balance, 9 and 18 g weights.
4. Babcock shaker.
5. Glassware: 8% milk bottles, 50% cream bottles, 50% Paley bottles, 17.5 ml cylinders, 17.6 ml pipette, .
6. Reagents: - Babcock sulphuric acid (Sp. Gr. 1.82-1.83)

• N-butyl alcohol
• Glymol.

Milk

1. Temper sample to 20C and mix by pouring gently from original container to a beaker of similar capacity 4-5 times.
2. Transfer 17.6 ml (18.0g) of milk to 8% bottle with 17.6 ml pipette. Allow pipette to drain then blow out the remaining drop into the bottle.
3. Add 17.5 ml sulphuric acid (Sp. Gr. 1.82-1.83) in at least three increments using special cylinder. Rotate bottle between thumb and fingers while adding acid to wash milk from neck. Mix thoroughly 2 min. after each addition of acid by moving the bulb of the bottle in rapid circular motion. Final colour of mixture should be chocolate brown.
4. Centrifuge 5 min.
5. Add distilled water at 60C to bring contents to within one-quarter inch of base of neck. Do not mix.
6. Centrifuge 2 min.
7. Add water at 60C to float fat into neck of bottle. Top meniscus should be about even with the top of the graduated portion. Do not mix.
8. Centrifuge 1 min.
9. Temper bottles in water bath at 55C for 5 min.
10. Measure length of fat column with dividers from top of upper meniscus to bottom of lower meniscus. Place one divider point at zero mark and read percentage fat by weight directly where other point touches the scale.

Cream and Cheese

1. Temper cream sample to 20C and mix. Grind cheese to small particles.
2. Weigh 9 g of cream into 50% cream bottle and add 9 ml of distilled water at 200C. Weigh 9 g of cheese into a 50% Paley bottle and add 10 ml of distilled water at 60C.
3. Add 17.5 ml sulphuric acid in at least three increments. Mix until colour is uniform chocolate brown and all cheese particles are dissolved.
4. Centrifuge 5 min.
5. Add distilled water at 60C to bring contents to within one-quarter inch of base of neck. Do not mix.
6. Centrifuge 2 min.
7. Add water at 60C to float fat into neck of bottle. Do not mix.
8. Centrifuge 1 min.
9. Temper bottles in water bat at 55C, for 5 min.
10. Place 4-5 drops glymol on the fat column letting these run down the side of the neck. Measure the length of the fat column from the demarcation between fat and glymol to the bottom of the lower meniscus.
11. Report fat in percent by weight.

Skim milk, Buttermilk, Whey

1. Temper sample to 20C and mix gently.
2. Transfer 2 ml N-butyl alcohol and then a 9 ml sample to an 18 g double neck bottle. Mix thoroughly with a circular motion.
3. Add 9 ml of Babcock sulphuric acid for skim milk or buttermilk, 7 ml for whey.
4. Centrifuge 6 min. Place bottles in the centrifuge cup with the small neck facing the outside.
5. Add water at 60C to bring contents 1 cm from the base of the neck. Do not mix. Centrifuge 2 min.
6. Temper bottles in water bath at 55C for 5 min.
7. Place a finger over the large neck and press down until the lower meniscus of fat in the small neck corresponds to a major division.

Cheese salt determination using the Volhard procedure is described below. Other methods which have proven to give accurate results are:

1. Automatic Chloride Titraters operate on the principle of coulometric silver ion generation to titrate chloride ions in the sample. When all chloride ions are titrated free silver ions cause a conductivity change which signals the end of titration.
2. Quantab Chloride Titrater depends on the reaction of chloride ions with silver dichromate, which is brown, to form silver chloride chromate ion and silver chloride which is white. The reaction takes place on a calibrated strip which permits direct estimation of chloride content.

Volhard procedure for salt determination

Apparatus and Materials

1. A torsion moisture balance
2. 250 ml erlenmeyer flask and a 500 ml beaker
3. Two graduated cylinders, one 50 ml and the other 100 ml
4. A 10 ml pipette and a 5 ml graduated pipette
5. Burette graduated in ml and 1/10 ml, and burette stand
6. An electric or gas hot plate
7. Chemically pure concentrated nitric acid
8. Saturated potassium permanganate solution
9. 0.1711 N potassium thiocyanate solution (contains 16.63 g per litre) in a brown glass bottle
10. 0.1711 N silver nitrate solution (contains 29.07 g per litre) in a brown glass bottle
11. A saturated solution of ferric ammonium sulphate
12. Sucrose
13. Boiling chips such as carborundum granules or glass beads.
14. Fume hood

Method

1. Prepare cheese sample as for cheese moisture test.
2. Weigh about 3 g cheese into a clean dry 250 ml erlenmeyer flask.
3. Add 10 ml of 0.1711 N silver nitrate solution as accurately as possible to the flask. If cheese contains more than 3% salt, add more silver nitrate.
4. Add 15 ml of the chemically pure nitric acid.
5. Add 50 ml of distilled water.
6. Add a few boiling stones.
7. Place flask on hot plate in fume hood and boil.
8. When contents of flask are boiling uniformly, carefully add 5 ml of saturated potassium permanganate. Continue boiling until purple colour disappears, then add a second charge of 5 ml of potassium permanganate. When purple colour again disappears, add another 5 ml of potassium permanganate. Continue boiling until all cheese particles are digested. To ascertain when digestion is complete, remove flask from hot plate and allow to stand quietly for a few moments. Undigested cheese particles will float upon the surface, while the white precipitate of silver chloride will sink to the bottom of the clear liquid. When no more white particles are seen upon the surface, digestion is complete.
9. Add sufficient distilled water to bring the volume up to approximately 100 ml. Allow precipitate to settle and very carefully pour off the liquid into a beaker. Be careful not to pour off any of the white precipitate of silver chloride.
10. Add 100 ml of distilled water to flask and swirl contents to wash precipitate.
11. Add 3 ml of saturated ferric ammonium sulphate as an indicator and titrate the excess silver nitrate with 0.1711 N potassium thiocyanate. A reddish colour denotes the end point.
12. The number of ml of 0.1711 N silver nitrate originally added minus the titration value found in step 11, divided by the weight of the cheese in the sample equals the percentage of salt in the cheese.

EXAMPLE

3.00 g of cheese to which 10.00 ml of 0.1711 N silver nitrate had been added gave a reading of 4.00 ml in Step 11.

4.00 ml 0.1711 N potassium thiocyanate required to combine with excess silver nitrate.

6.00 ml 0.1711 N silver nitrate combined with salt in cheese.

Therefore per cent salt by weight = 6.00/3.00 = 2.00

Because the salt in the cheese is measured by its chloride content, it is necessary to test the reagents used for chloride, or related substances content. This is done by carrying out a test using sucrose instead of cheese. The titration value subtracted from the original amount of silver nitrate added is subtracted from the value found in Step 12 before dividing by weight to find the percentage salt in the cheese.

To check the strength of the 0.1711 N silver nitrate solution, dissolve 10 g chemically pure dry sodium chloride in sufficient water to make up one litre of solution. Each ml of this solution is equivalent to one ml of 0.1711 N silver nitrate. When the silver nitrate has been standardized, each ml of silver nitrate is equivalent to one ml 0.1711 N potassium thiocyanate.

Purpose

This simple test is useful to ensure that cheese cultures have adequate activity before inoculating the cheese vat. For most cheese a general rule of thumb is that the activity and amount of inoculum should be sufficient to produce a titratable acidity of about .34% lactic acid, in 10% reconstituted skim milk, after 4 h of incubation at 37C. The test is also useful to compare types of cultures or bulk cultures prepared under different conditions. For these purposes a pH versus time chart is quite useful . A further application is to check sensitivity of the culture to bacteriophage in the plant (see next section Detection of Bacteriophage and Figure 3.1).

Procedure

1. Mix 10 g of low-heat, antibiotic-free skim milk powder in 90 ml of distilled water in a 100 ml Erlenmeyer flask.
2. Sterilize at 15 lb pressure (1.05 kPa.) for 10 min.
3. Cool to 37C.
4. Inoculate with 3.0 ml starter or other amount as appropriate. Rinse pipette twice by drawing the sterile milk into it.
5. Incubate at 37C for at least 4 h. Longer if desired for pH versus time profile.
6. Check pH at 30 min. intervals.
7. Titrate 17.6 ml with N/10 sodium hydroxide (NaOH) using 1 ml phenolphthalein. Divide the required ml of NaOH by 2 the obtain titratable acidity in units of percent lactic acid.
8. Record starter activity as follows:
   Active, over 0.34%
   Slow 0.26 to 0.30%

Figure 3.1 Culture Activity Test

The following tests are based on the principle that bacteriophage specific to the culture in use will be present in high numbers in the cheese whey. Therefore, by monitoring whey for the presence of phage "a dead vat" on subsequent days can be avoided.

Culture Activity Test

The culture activity test described above can be used to detect the presence of phage in cheese whey. Prepare 300 ml of reconstituted skim milk and place 99 ml in each of three beakers. Add 1 ml of whey to Beaker 1 (100 x dilution), then transfer 1 ml from Beaker 1 to Beaker 2 (10,000 x dilution) and finally, transfer 1 ml from Beaker 3 to Beaker 4 to make a 1 million times dilution. Add culture and monitor pH as described in section 3.8.

Bromocresol Purple (BCP) Phage Inhibition Test

This test is quite simple to perform, and produces more accurate results than the culture activity test.

1. Prepare Materials

• BCP stock solution (1 g/100 ml water)
• Test tubes containing 9.9 ml sterile BCP-milk (5 ml BCP stock solution/litre milk)
• 30-32C water bath or heating block
• 1 ml graduated pipettes
• Membrane filter (0.45 u) -- optional
• Disposable syringe -- optional
• Clinical centrifuge -- optional
• Whey sample for phage testing
• Freshly grown culture, frozen syringe, or frozen can of each strain

2. Add Whey to BCP Milk and Make Dilutions

Transfer 0.1 ml of fresh (or filter-sterilized) whey to the first dilution tube (10-2) and mix well. Transfer 0.1 ml from the first to the second dilution tube and mix well. Repeat process for the third dilution tube. (If unfiltered whey is used, a control tube containing BCP milk and whey only, must be prepared. This control tube tests for the presence of active culture in the whey that could mask phage inhibition of a strain.) Whey samples should be refrigerated immediately after collection and held cold until tested for phage.

3. Add Culture to Control and Whey Dilution Tubes

Cheese culture (0.2 ml) is added to whey dilution tubes and to a control tube for each strain. If you are using direct-to-the-vat culture, dilute 1 ml of culture in 9 ml of milk and then add 0.2 ml of the mixture to the dilution tubes. The control tube contains only BCP milk and culture---NO whey. The control tube serves to show starter strain inhibition by colour comparison with the other tubes.

Incubate Tubes and Interpret Results. Incubate both control and dilution tubes for 6 hours at 30-32C. Compare the colour of the whey dilution tubes to that of the control tube. Ignore coagulation. An uninhibited culture will produce sufficient acid to turn the BCP dye from blue to yellow. Strains should be removed from the culture blend when full inhibition persists at the 10-6 dilution level. The following system should be used to record phage inhibition:

0 = No inhibition at any dilution

1 = Partial inhibition at 10-2 dilution

2 = Full inhibition at 10-2 dilution

3 = Partial inhibition at 10-4 dilution

4 = Full inhibition at 10-4 dilution

5 = Partial inhibition at 10-6 dilution

6 = Full inhibition at 10-6 dilution

This section is adapted from two reports prepared by: Mark Mitchell (1995), Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph, Ontario

Regulations

Most jurisdictions have regulations concerning the testing methods and limits of certain antibiotics in raw milk. The Milk Act of Ontario, Regulation 761, Section 52, Subsection, states:

"The milk of every producer shall be tested at least once a month for the presence of an inhibitor by an official method."

An official method is described in a separate inhibitor policy document which states:

The minimum sensitivity of an official method to test for the presence of an inhibitor under section 52 of Regulation 761 shall be:

1. 0.01 international units of penicillin per millilitre of milk by the Standard Disc Assay (Bacillus stearothermophilus) procedure.
2. 10 parts per billion sulfamethazine by the High Performance Liquid Chromatography (modified Smedley and Weber) procedure.

A concentration of .01 international units of penicillin per millilitre of milk is equivalent to 6 parts per billion (ppb). Note: 1 ppb is equivalent to a single penny in $10 million or one second in 32 years.

Detection Methods

It is beyond the scope of this manual to discuss any specific methods in detail. What follows is are brief descriptions of five types of inhibitor tests which are currently used in the dairy industry. For each category one or more brand name tests are listed to indicate possible choices. For cheese manufactures seeking assistance with inhibitor testing, there are many private labs which provide suitable services. In Ontario, a wide range of expertise and methodologies are available from Laboratory Services Division, University of Guelph.

Growth Inhibition Assays

Examples: Delvotest P, Delvotest SP, BR test, BR-AS test, Charm Farm, and the Disk Assay

This test format involves a standard culture of a test organism in an agar growth media, usually Bacillus stearothermophilus, that is inoculated with a milk sample and incubated for periods of up to several hours. If the milk contains sufficient concentrations of inhibitory substances the growth of the organism will be reduced or eliminated. The presence of an inhibitory substance is indicated by zones of inhibition or a change in colour of the media (pH and redox indicators).

The major disadvantages of these tests are that they are not very specific for identification purposes, have limited sensitivities to many antibiotics and take a long time before results are available. Growth inhibition tests are only able to classify residues into either the ß-lactam (penicillin like antibiotics) or other than ß-lactam antibiotic families. A further concern is that growth inhibition tests are subject to the effects of natural inhibitors (eg. lysozyme, lactoferrin, complement and defensins) which can be found in high levels in mastitic milk and may give false positive test results, particularly when used at the cow level. These effects can be minimized by heating individual cow samples at 82C for 2-3 minutes in a microwave oven or water bath before testing to destroy natural inhibitors and allow antibiotics which are more heat stable to remain.

The advantages of these tests are that they are cheap, easy to perform and have a very broad detection range.

Enzymatic Colorimetric Assays

Example: Penzyme Test for ß-lactams

The penzyme test is based on the inactivation of an enzyme by ß-lactam antibiotics. The enzyme (DD-carboxypeptidase or penicillin binding protein) is present in all bacteria and is involved in the synthesis of the bacterial cell wall. ß-lactam antibiotics will bind specifically with this enzyme and block it's activity, thus preventing the formation of the bacterial cell wall. This enzyme has been freeze dried and placed in sealed vials to which the milk sample is added. After addition of 0.2 ml (200 µl) of milk sample to the vial the sample is incubated for 5 minutes at 47C. During this time any ß-lactams present in the milk bind to the enzyme and inactivate a certain amount depending on the concentration present.

Reagent tablets specific for the enzyme (D-alanine peptide and D-amino acid oxidase) are then added to the milk sample and the sample is incubated at 47C for 15 minutes. During incubation any remaining active enzyme will react with the reagent added. The end product of the substrate and enzyme reaction (pyruvic acid and hydrogen peroxide) is measured by a redox colour indicator and the final colour is compared to a colour chart provided with the kit.

An orange colour (reduced) indicates a negative test result.

A yellow colour (oxidized) indicates a positive test result.

Microbial Receptor Assays:

Example: Charm II

This test uses bacterial cells (Bacillus stearothermophilus), which contain natural receptor sites on or within the cells for antibiotics, and radio labelled (C14 or H3) antibiotics. Milk sample is added to a freeze dried pellet of bacterial cells (binding reagent) in a test tube and the sample is mixed and incubated. During incubation any antibiotic present in the milk will bind to it's specific receptor site. Radio labelled antibiotic (tracer reagent) is then added and the sample is mixed and incubated. Unbound receptor sites on the bacterial cell will be bound by the radio labelled antibiotic. The sample is then centrifuged to collect the bacterial cells in the bottom of the test tube and the supernatant and butterfat is discarded. The bacterial cells are then resuspended and mixed in scintillation fluid. Binding is measured with a scintillation counter and compared to a positive and negative control. The more antibiotic present in the sample the lower the scintillation counts determined by the equipment.

Charm currently has test kits in this format for ß-lactams, macrolides, aminoglycosides and sulfonamides.

Immunoassays

Unlike other residue testing methods immunoassays are fast, sensitive, inexpensive, reproducible, reliable and simple to perform. The technique depends upon the measurement of the highly specific binding between antibodies (Ab) and antigens (Ag). Antigens are substances which are foreign to the body (eg. bacteria, viruses, toxins, pollens, drugs, hormones and pesticides) and that when introduced into the body give rise to the production of antibodies. Antibodies are proteins produced in the body by white blood cells (lymphocytes) as a result of exposure to antigens (destroy invading pathogens). The extreme sensitivity of the immunoassay is due to the development of certain labelling techniques for molecules (conjugates), enabling the measurement of very small masses (picogram or parts per trillion) of substances.

Immunoassays are classified according to the label which is attached to either the antigen (the anolyte being measured) or the antibody. The label may be a radioactive atom as in radio immunoassays (RIA), or an enzyme as in enzyme immunoassays (EIA or ELISA (Enzyme- linked immunosorbant assay)) or a fluorescent substance as in fluorescence immunoassays (FIA).

There are 3 major types of immunoassays used commonly for the detection of antibiotics in milk:

1. Enzyme-Linked Immunoassay (eg. LacTek tests, SNAP for Tetracyclines, Single Step Block for SMZ)
2. Enzyme-Linked Receptor Binding Assay (eg. SNAP for ß-lactams, Delvo-X-Press)
3. Radio immunoassay (CHARM II for tetracyclines and chloramphenicol)

Coagulation Time versus Setting Time

Rennet is generally described in the industry as single, double or triple strength. Single strength is considered to be that concentration where 200 ml is sufficient to set 1,000 kg of milk in 30 - 40 min. at 30 - 32C. Setting time is the point where the curd will break cleanly and exude clear whey. Coagulation time is the point where flecks of curd first appear on a spatula or slide dipped into the milk. Coagulation time is about half of setting time, so typically, coagulation using single strength rennet requires 15-20 minutes followed by setting at 30-40 minutes. The following simple test can be used to check coagulation time which can be measured much more accurately than setting time. The test uses skim milk because the presence of fat globules makes it difficult to see the first sign of coagulation.

Measurement of Coagulation Time

1. Prepare 200 ml samples of 10% reconstituted low heat skim milk powder in 250 ml beakers. Add 0.02% calcium chloride dihydrate (40 mg per 200 ml).
2. Temper to 32C in a water bath.
3. Add 1.0 ml of 5% rennet solution to each sample.
4. Determine the clotting time by dipping a clean spatula or glass slide into the milk. When coagulation has occurred flecks of curd will appear in the milk film on the slide.

Relative Milk-Clotting Activity Test

A more rigorous test of coagulant activity is the "Relative Milk-Clotting Activity Test" (RMCAT) which measures the activity of rennet and other coagulants in "International Milk-Clotting Units" (IMCU). The method is described in International Dairy Federation standard 157:1992.

Selective media for yeasts and moulds include acidified media and antibiotic media. The method described below uses acidified potato dextrose agar.

Equipment and Material

Potato dextrose agar

Equipment for plating

Tartaric acid solution (10 aqueous)

Incubator set at 22-25C

Procedure

1. Prepare cheese homogenates and serial dilutions as described in Section A.
2. Predetermine the quantity of sterile 10% tartaric acid solution necessary to obtain a pH of 3.5 + 0.1. Put a portion of the medium in a small beaker and titrate to pH 3.5 at 45C. Check the accuracy of the titration by allowing the agar to cool to incubation temperature, place electrodes directly into the solidified medium, and read the pH. It should be 3.5 + 0.1. Calculate the amount of sterile 10% tartaric acid solution necessary for the volume of tempered agar to be used for pouring plates.
3. Place 5 ml of the 0.1 dilution and 1 ml of additional dilutions as required into each of duplicate petri dishes.
4. Add the tartaric acid solution to the tempered agar immediately before pouring 15 - 20 ml into each of the plates containing the sample dilutions.
5. Mix well and let solidify before inverting the plates. Incubate at 22 - 25C.
6. Count the plates at 3 and 5 days of incubation. Yeast cells will appear as cream coloured shiny colonies.

• Prepare cheese homogenates and serial dilutions as described in Section A.
• Place 5 ml of the 0.1 dilution (= 0.5 g of original sample or Omega dilution) and 1 ml of additional dilutions as required into each of duplicate petri dishes and add molten VRB agar. (Note: Do not sterilize VRB agar.) When solidified, pour over layer (5 ml VRB).
• Incubate at 35C + 10C for 18 - 24 hrs.
• Count the dark red colonies, at least 0.5 mm in diameter, and record results as coliforms per g of sample.

Samples of cottage cheese and other acid milk products should be plated within 24 hrs. after manufacture because coliform counts decline under acid conditions. Coliforms also decrease in number during aging of ripened cheese varieties.

It must be emphasized that this method provides a presumptive count only. If presumptive counts are consistently high, colonies should be confirmed (see Standard Methods). The Canadian Food And Drug Act and Regulations permit 500 coliforms/g of cheese made from pasteurized milk and 5,000 coliforms/g of cheese made from unpasteurized milk. Permitted counts of Eshericia coli are 100 and 500/g respectively.

Procedure A

The method described here enumerates total Staphylococci by surface plating on Baird-Parker media. A coagulase test can be used to determine if individual colonies are S. aureus. Canadian Food And Drug Act and Regulations permit up to 100 coagulase positive S. aureus in pasteurized milk cheese and up to 1,000/g in cheese made from unpasteurized milk.

Equipment and Materials

Plating equipment

Glass spreaders (hockey stick-shaped glass rods)

Incubator set at 37C

Baird-Parker Agar

Procedure

1. Pour plates of B.P. agar (15 ml/plate) and dry surfaces (using sterile laminar airflow cabinet -- 2 hrs).
2. Pipette 0.1 ml of homogenate and of subsequent dilutions onto surface of agar and spread evenly with a sterile bent glass rod until surface appears dry. Prepare duplicate plates. Use 10-1, 1--2, and 1--3dilutions.
3. Incubate at 37C for 48 hrs.
4. Count the number of colonies in each of the following groups:
   1. convex, shiny, black, with or without narrow gray-white margin, surrounded by clear zone extending into opaque medium.
   2. convex, shiny, black, with or without narrow gray-white margin, surrounded by clear zone extending into the opaque medium with an inner opaque zone.
   3. convex, shiny, black, with or without narrow gray-white margin, >1 mm in diameter.

Procedure B

Pipette 1 ml or 0.1 ml of homogenate and of subsequent dilutions into petri dish.

Add approximately 10 ml Baird-Parker medium. Mix well. Let stand on bench.

When solidified, invert and put in incubator at 37C (for 48 hours).

Read the same as Procedure A.

Note: Add 5 ml of well mixed Ey Tellurite, enrichment, at 5C to Baird-Parker agar prior to pouring plates.

This section is adapted from two reports prepared by: Mark Mitchell (1995), Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph, Ontario

Figure 3.1. Culture activity test: example.

Conditions

Culture Lactococcus lactis subsp. lactis

Lactococcus lactis subsp. cremoris

Temperature 37 C

Inoculum 2% of mother culture prepared with 10% reconstituted skim milk powder.

Test media 1 10% skim milk powder, low heat, antibiotic free.

Test media 2 Same as one with 1% cheese whey.

Results

Titratable acidity after 4 hours:

Treatment 1 0.34%

Treatment 2 0.25%

pH versus time

Interpretation

1. Test media 1 shows normal growth. 0.34% acidity after 4 h with a 2% inoculum is adequate for most types of cheese. pH versus time plot is typical, reaching pH 5.2 between 6 and 7 hours.
2. Test media 2, containing cheese whey, shows inadequate acid development, indicating the probable presence of bacteriophage in the cheese plant.

Species 

Cheese making principles are similar for milk of all species with some modifications required to account for high solids of some species such as buffalo and sheep. Cows' milk and goat's milk have similar cheese making properties except that:

• Goats' milk cheese tends to ripen by lipolysis (fat breakdown) more than cows' milk cheese.
• Goats' milk has smaller fat globules which allows higher fat recovery and possibly a smoother texture..
• Cheese making quality of goats' milk is also improved due to higher levels of alpha-S1 casein in goats' milk which permit better coagulation.

Genetics

Through out the modern history of dairying, farmers have selectively bred dairy cattle to increase production or fat content or both. Recently, genetic selection has focussed on other milk properties such as increasing the proportion of milk protein to fat. Three genetic effects are most relevant to cheese making.

(1) Relative proportions of fat and protein (P/F ratio)

Fat content and protein content generally increase or decrease in parallel, but fat varies more with feed and season then protein. The same is true for breed (genetic) effects, such that genetic selection has produced the the following practical effects in modern dairying.

• Higher fat breeds have lower protein/fat ratio. For example, a typical protein/fat ratio in Jersey milk is 0.7 relative to 0.84 in Holstein milk (Table 4.4).
• Genetic selection over the last 100 years has produced considerable within breed improvement with respect to both milk production and increased protein and fat content. The result is greatly increased per cow production of milk protein and fat. However, once again, because fat responds more to genetic selection than protein, the result in many areas has been a gradual decrease in the average P/F ratio. For example in Ontario, the P/F ratio decreased from about 0.88 in 1970 to 0.85 in 1995 (estimated from data provided by Laboratory Services Division, University of Guelph.

(2) Relative proportions of fat and protein to other solids

With respect to other solids, mineral content (mainly Ca, Mg, and P) generally varies in proportion to protein content and lactose content is relatively stable. Because lactose is largely a wasted component, increasing protein and fat by feed or genetic selection has economic advantages in terms of feed conversion, milk transportation costs, and waste handling.

(3) Stage of lactation

Fat content tends to increase during lactation as milk production decreases. The result is that the relative proportion of protein to fat (protein/fat ratio or P/F) is highest at the peak of lactation (about 60 days of lactation) and lowest at the end of lactation. Protein distribution also changes during lactation with resulting effects on cheese ripening and flavour. In particular, the proportion of alpha-caseins decrease during lactation while the proportion of beta-casein increases.

Feed

Depending on the relative demand for butter fat versus milk non-fat solids, there may be incentive to change the relative proportions of milk protein and fat. The only short term means to do this is by changing the diet. Generally less roughage and more high energy feeds will encourage lower fat content with little decrease in protein content to provide a higher P/F ratio.

Season

Seasonal variation in milk composition is most important to cheese yield efficiency and composition control. Some important seasonal effects are listed below and illustrated to the right. These observations are based on Ontario data.

• Fat content reaches a minimum in August and a maximum in October.
• Protein content changes roughly in parallel with fat content, but the seasonal variations are smaller, causing high protein fat ratios (P/F) during the summer and low P/F ratios in the winter.
• Casein content also varies with season which is most important because cheese making is dependent on casein NOT on total protein (more on this in Treatment of milk for cheese making, Standardization of milk for cheese making and Yield efficiency).

Cheese making depends on the growth of bacteria to produce acidity, flavour compounds, and ripening enzymes. It is, therefore, important to understand the characteristics of milk as a growth medium.

General Nutrients

Milk is a good source of all principal nutrients, including carbon, nitrogen and macro-minerals. Many micronutrients such as vitamins and micro-minerals are also available. However, milk is unique with respect to its sugar.

Milk Sugar

Carbohydrates, especially simple sugars such as sucrose (table sugar), can be utilized as sources of energy more quickly than fats and proteins. However, the energy currency of the cell is glucose (also called dextrose) so to use available carbohydrates, microorganisms must be able to convert them to glucose.

The only sugar naturally present is milk is lactose. Most microorganisms lack the enzyme lactase which is required to break lactose into its two component sugars, namely, glucose and galactose. Lactic acid bacteria which do have lactase readily break down lactose and use glucose as an energy source. Lactic acid bacteria, therefore, have a competitive advantage in milk; that is, they are able to out grow other bacteria which are unable to obtain glucose from lactose. Further, some lactic acid bacteria are able to convert galactose to glucose.

Acidity (pH)

Acidity as measured by pH is one of the most critical parameters with respect to both food safety and both process and quality control of fermented foods such as cheese. The concepts of acidity and pH are explained in Sections 3.5. The titratable acidity of milk typically varies from 0.12 to 0.19% lactic acid depending on composition, especially protein content. The pH of milk is near the physiological pH of 6.8 which, considering the following points, means that milk is a good growth medium with respect to acidity (pH).

• Most organisms grow best at pH near physiological pH of 6.8. As explained in Section 3.5, titratable acidity (TA) is not a good predictor of acid effects on microbial growth and chemical properties such as protein functionality.
• The major groups of microorganisms important to food preservation are in order of increasing acid tolerance: bacteria, yeasts and moulds.
• Natural fermentation of warm raw milk by lactic acid bacteria reduces milk pH to less than 4.0 which prevents the growth of pathogenic bacteria and most spoilage bacteria

Moisture

Milk has a high moisture content (typically 87% for cows' milk) and with respect to available moisture, is an excellent growth medium. But, it must be understood that with respect to microbial growth, the critical parameter is water activity not moisture content. Water activity (aw) is an index of the availability of water for microbial growth. It is the availability of water in the food reported as a fraction of the availability of water from pure water. In other words, the aw of water is 1 and the aw of other substances is reported as decimal fractions of 1. Water activity is reduced by dissolved substances, varying directly with number of dissolved molecules rather than the weight. For this reason, relative to large molecules such as proteins, small molecules such as sugar and salt have a large effect on water activity. For example, jams are preserved by their high sugar content.

Microorganisms vary greatly in their ability to survive and/or grow at reduced water activity. However, acknowledging that exceptions exist, the minimum water activity for the principal groups of microorganisms are as follows:

• Most bacteria: 0.90 - 0.91
• Most yeast: 0.87 - 0.94
• Most moulds: 0.70 - 0.80

Compare these values with typical aw values for milk, cheese and a few other foods.

• Milk, fresh fruits and vegetables, fresh meats 60 - 98% moisture, aw 0.97 - 1.00
• Most baked products, some cheese, some cured meats, 20-60% moisture, aw 0.88 - 0.96.
• Dehydrated foods such as breakfast cereals. Less than 5% moisture, aw 0.20 - 0.30

Typical aw values for some cheese at the marketing stage are given below (Eck and Gillis, 2000). See also typical aw values for cheese families in Table 1.1.

Availability of oxygen

• Cottage 0.988
• Brie 0.980
• Munster 0.977
• Saint-Paulin 0.968
• Edam 0.960
• Cheddar 0.950
• Parmesan 0.917

Availability of oxygen

With respect to oxygen requirements, microorganisms may be:

• Aerobic: must have oxygen to grow
• Anaerobic: can only grow in the absence of oxygen
• Microaerophilic: require small amounts of oxygen
• Able to grow with or with out oxygen.

Moulds require oxygen, so they can be eliminated by vacuum or gas flush packaging. Most yeast are aerobic (require oxygen) but some can grow anaerobically (in the absence of oxygen). Bacteria may fall into any of these categories, but lactic acid bacteria are micoaerophilic or anaerobic.

Milk will acquire some dissolved oxygen during milking, storage and handling, but it is used up quickly during bacterial growth.

The numbered list below identifies seven types of bacteria according to how they change the properties of milk. Often these changes are negative (spoilage) but as we will see in later sections, many of these bacteria are important to the development of cheese flavour. Before proceeding to the list, please note the following definitions:

• Psychrotrophic refers to microorganisms which are able to grow at temperatures less than 7C. Cold milk storage and transport selects for psychrotrophic bacteria which are often proteolytic and lipolytic. Common psychrotrophic bacteria in milk are species of Micrococci, Bacilli, Staphyloccoci, Lactobacilli, Pseudomonas, and coliforms. Pseudomonas species are the most common and typically have the most impact on quality. At temperatures of 2 - 4C, bacterial growth in milk is mainly due to strains of Pseudomonas flourescens. Little growth occurs at temperature less than 2C.
• Spore forming bacteria are able to exist in a highly stable form called 'spores'. In the spore state, these bacteria are able to withstand greater extremes of acidity, temperature and desiccation.
• Enzymes are biological catalysts that accelerate the rates of biochemical reactions. Bacterial enzymes are most significant to milk spoilage and cheese ripening but it is important to distinguish between the enzyme and the bacterial source. For example, many psychrotrophic bacteria produce heat stable enzymes which remain active in milk and cheese even after the bacteria are killed by pasteurization.

Keeping the above definitions in mind, note the following types of microorganisms, grouped according to their impact on milk quality.

(1) Lactic acid bacteria which ferment lactose to lactic acid and other end products. Lactic acid bacteria (LAB) important to cheese making will be described further in Cultures. For now note the following:

• As noted earlier, LAB are able to readily metabolize lactose so they have some competitive advantage over other microorganisms.
• Notwithstanding, their ability to metabolize lactose, LAB prefer temperatures greater than 30C, so, depending on initial relative counts, psychrotrophic bacteria including some coliform and pseudomonas bacteria are able to outgrow LAB at room temperature.

(2) Proteolytic bacteria which degrade protein and cause bitterness and putrefaction. Most important in cheese milk are species of:

• Pseudomonas which are psychrotrophic and produce heat stable lipases.
• Bacillus which form heat stable spores and survive pasteurization

(3) Lipolytic bacteria which degrade fats and produce lipolytic rancidity. Again, the most common example in milk is the genus Pseudomonas. Several psychrotrophic species of Pseudomonas produce heat stable lipases as well as proteases.

(4) Gas producing microorganisms which cause cheese openness, floating curd in cottage cheese, and gassy milk.

• Yeasts are always present in milk and are common contaminants during the cheese making process. They may cause 'yeast slits' in cheese and contribute to ripening of surface ripened cheese.
• Coliform bacteria are always present in milk but their numbers can be minimized by good sanitation. Also, coliform bacteria compete poorly with lactic acid bacteria, so their numbers rapidly decrease in the presence of a rapidly growing lactic acid culture.
• Clostridium tyrobutyricum is a thermoduric (survives pasteurization) spore forming organism of legendary fame among cheese makers. C. tyrobutyricum causes gas formation (carbon dioxide) during the later stages of ripening of Swiss and Dutch type cheeses. The resulting craters and cracks in the cheese are called 'late gas defect'. European cheese makers frequently check raw milk for thermoduric and/or spore forming bacteria to estimate potential for late gas defects. Five hundred spores per litre of milk are sufficient to cause late gas defect.
• Propioni bacterium produces the desirable gas formation in Swiss type cheese.
• Some lactic cultures, called heterofermentative, also produce carbon dioxide. See Cultures. 

(5) Ropy bacteria cause stringy milk due to excretion of gummy polysaccharides. Usually ropy bacteria such as Alcaligenes viscolactis are undesirable. However, in some fermented dairy products, ropy lactic acid bacteria such as certain subspecies of Lactococcus lactis are used to develop texture.

(6) Sweet curdling bacteria produce rennet-like enzymes which may coagulate milk. Common examples are the psychrotrophic spore formers Bacillus subtilis and Bacillus cereus.

(7) Numerous off flavours have been associated with specific milk contaminates. Some examples are:

• Malty: S. lactis var maltigenes
• Bitter: see (2) Proteolytic bacteria
• Rancid: see (3) Lipolytic bacteria
• Unclean: coliform bacteria
• Fishy: Pseudomonas
• Fruity: Pseudomonas 

This short course makes no attempt to provide comprehensive training on food safety with respect to cheese manufacture. However, some food safety principles will be discussed in the context of other topics, for example, acid control and food plant sanitation. Here, we mention only some characteristics of a few pathogens which are particularly significant to cheese making. We begin with definitions to distinguish between food infection and food intoxication.

Food infections are caused by organisms which grow in the gastro intestinal track. Illness occurs after ingestion of an infectious dose which depends on many factors including the health status of the person.

Food intoxication results from toxins produced by bacteria. Toxins may be present within the bacteria (endotoxin) or excreted outside the bacteria (exotoxin). The organism need not be alive or even present to cause illness. A good example, is Staphylococcus aureus. Like all the other pathogenic bacteria listed below, Staphylococcus aureus is destroyed by pasteurization but its enterotoxin survives pasteurization.

Pathogens: common before 1940

• Corynebacterium diptheriae: causes diphtheria
• Brucella abortus: causes brucellosis in cows and undulant fever in people.
• Mycobacterium tuberculosis: causes TB in people.
• Coxiella burneti: causes Q fever in people.

Pathogens which emerged during 1940 - 1970

• Staphylococcus aureus: food intoxication caused by heat stable enterotoxins of which enterotoxin A is the most common.
• Salmonella species: Salmonellosis is an infection caused by many species and strains of species of Salmonella. Salmonellosis is of great concern to the dairy industry, especially the cheese and milk powder sectors. Infectious doses can be extremely low, perhaps as low as a single organism.
• Enteropathogenic E. Coli produce enterotoxins, some of which are heat stable. Of numerous species and strains, the most famous is E. Coli 0157 H7, which occurs frequently in raw milk. E. Coli0157 H7 is of particular concern because it is quite acid tolerant and is able to grow at refrigeration temperatures.

Recent Pathogens

• Yersina enterocolitica is a psychrotrophic infectious agent.
• Campylobacter jejuni, is an infectious agent which has passed Salmonella as the leading cause of diarrhoea all over the world.
• Listeria monocytogenes is a psychrotrophic infectious agent, which requires special caution because it is acid tolerant and more heat stable than most pathogens, although it does not survive proper pasteurisation.
• Bacillus cereus is mainly important as spoilage agent. However, some strains are mildly pathogenic which is problematic because Bacillus cereus forms heat stable spores which survive pasteurization and are able to grow at refrigeration temperatures.

Lactic cultures are very sensitive to antibiotics. In most jurisdictions increasing penalties have greatly reduced antibiotic residues in milk. Nevertheless, antibiotic testing of all cheese milk is still recommended. See rapid screening tests in Section 3.10.

Mastitis is an infection of the udder which negatively impacts milk quality. Pooling milk dilutes the effect of single infected cows and herds but in most jurisdictions the cumulative effect of mastitis, especially subclinical mastitis, is significant. Olson as cited in Eck and Gillis (2000) estimates a cheese yield loss of 1% if 10% of the milk is from cows with subclinical mastitis. Further, as noted below, the quality effects of mastitic milk are probably of more economic importance than the yield effects.

Causative organisms include human pathogens such as E. coli and Staphylococcus aureus. Nonbacterial infections such as prototheca infection also cause high SCC. Based on new automated procedures for bacteria counting, Ontario producer milk data suggests that prototheca is a common mastitic agent and frequently contributes to high SCC and bacterial counts.

Typical Ranges of Somatic Cells

Somatic cells include any type of 'body' cell in the milk, such as skin cells (epithelial) from the cows' udders and leucocytes of several types. Leucocytes are white blood cells which are part of the cow's immune response to infection in the udder, so they are used as an index of mastitis or udder infection. Several observations are relevant:

• The milk of healthy cows should contain less than 100,000 somatic cells per ml of milk. Higher counts indicate subclinical mastitis (infection in the udder).
• Clinical mastitis is associated with counts greater than 1,000,0000/ml
• Producer milks in Ontario average about 200,000 cells/ml but counts less than 100,000 can readily be achieved with good herd management

Critical Ranges With Respect to Milk Quality

There is evidence that counts as low as 100,000 cells/ml affect cheese yield (Barbano et al, 1991, J. Dairy Sci. 74:369) and the quality of other dairy products such as ultra-high temperature milk. SCC in the range of 250,000 - 500,000 are associated with altered milk composition and decreased cheese yield. When counts exceed 1,000,000 cells/ml, altered milk composition and reduced cheese yield, are obvious.

Composition Effects

Gross composition effects of udder infection are not significant for SCC less than about 250,000/ml. Above that level the following trends are observed:

• Little change in fat content
• Increased mineral content, particularly more cloride.
• Decreased lactose content which balances the osmotic effects of increased mineral content.
• Protein effects:
  • Less casein
  • More whey proteins, especially immunoglobulins
  • More nonprotein nitrogen

Increased pH (up to 7.5 whereas 6.7 is normal)

Bacteriological Properties:

High SCC are normally associated with shedding of pathogenic (to humans) bacteria in the milk including E. coli, S. aureus and others. Basically, whatever organism is causing the udder infection, including the algae, prototheca will be present in the milk. Further, growth factors present in high SCC milk encourage growth of both E. coli and S. aureus (Amer. J. Vet. Res. 45:2504). The growth rates of some lactic cultures are also affected; Streptococcus thermophilis grows faster and Lactobacillus acidophilus is inhibited.

Significance To Cheese Milk

Cheese yield is affected in two ways:

• Mastitic milk contains more plasmin, a heat stable milk protease which degrades protein and causes more protein to be lost in the whey.
• Reduced casein directly affects cheese yield.
• Poor curd formation (longer flocculation time, slower rate of curd firming, and reduced maximum firmness) contributes to yield loss as fines.

Perhaps more important than yield are the effects of subclinical mastitis on cheese quality (J. Dairy Res. 53:645). Modest levels of SCC cause several quality problems:

• Decreased curd strength due to high whey proteins, low caseins, high pH and altered calcium-phosphate-caseinate balance. As noted above, these changes affect cheese yield, but they also impact quality.
• Higher moisture cheese due to impaired curd syneresis.
• Soft, less elastic, sticky and grainy cheese texture.
• Increased flavour intensity, usually with off flavours

Significance to Fluid Milk

Very high counts (>2 million) will cause milk to taste salty and result in many quality problems. Lower counts, even as low as 300,000 can increase development of bitter flavour due to increased levels of plasmin. This is a particular problem with ultra-high-temperature processed milk because the enzyme is heat stable and the storage time is long enough to permit significant protein degradation.

The following list is a summary of the most important raw milk quality tests. Procedures for some milk quality tests are described in Process and quality control procedures.

1. Organoleptic
2. Total plate counts: good < 3,000/ml; maximum raw milk 100,000
3. Coliforms: good < 10/ml; concern > 25; max 100
4. Psychrotrophes (grow at T < 7C): good < 1,000
5. Somatic cell counts: good <100,000; concern >300,000;
6. Rapid test for inhibitors
7. Disk assay (official test for inhibitors)
8. Added water: maximum freezing point -0.505C (-525H)
9. Composition: fat, protein, lactose, total solids, and casein if possible.

In addition to standardization of microflora, it is normally necessary to adjust milk fat or protein or both. The objective of milk composition standardization is to obtain the maximum economic return from the milk components. In practice, this means that milk composition is adjusted to achieve the most economically favourable balance of the cost of ingredients and the percent transfer of milk solid components to cheese while maintaining cheese quality.

Cheese yield is mainly determined by the recoveries of protein and fat in the cheese (that is the percent of fat and protein transferred from milk to cheese) and by cheese moisture, but other components also contribute significantly. Cheese yield is discussed in Yield efficiency. Standardization of milk for cheese making is a detailed practical guide to milk standardization, including the necessary calculations for manual standardization. Here we summarize general considerations on milk standardization. 

Government standardized cheese varieties

Food regulatory agencies in many jurisdictions have mandated standardized foods for which specific criteria with respect to composition and/or quality must be met. Section 28 Table Part 1, Canada Agricultural Products Act and Regulations lists maximum moisture and minimum fat levels (percent by weight) for 46 cheese varieties. No other composition or quality standards are prescribed, so, the identities of cheese varieties are not protected. For example, American mozzarella is NOT pasta filata cheese like Italian stretch mozzarella, but it is mozzarella according to Canadian regulations. 

Cheese fat on a dry matter basis

Table 6.1 includes data for target fat and moisture content according to the respective minimum and maximum values as prescribed by the Canada Agricultural Products Act. It also includes a column for fat in the dry matter (FDM) which is the target cheese fat content reported as a percentage of the target total solids content, where total solids is calculated as 100 minus the target moisture content. Because the principal nonfat component in cheese is casein, the target FDM value is useful to estimate the proportions of fat and protein required in the cheese milk. For example cheese makers generally consider a full fat cheese contains 50% FDM which corresponds to a protein fat ratio in the cheese milk of 0.94 - 0.96. By this criteria, both Cheddar and Feta are full fat cheese because they both contain about 50% FDM, although on a wet basis their respective fat contents are 31 and 22%. 

Protein/fat ratios (P/F)

P/F (ratio of protein to fat) is exactly what the name implies. Having no units, it is an index of the relative proportions of fat and protein in the milk. Please be clear that the P/F value indicates nothing about the absolute value of fat and protein. P/F ratio is generally lower in low fat milk and higher in high fat milk, so that Jersey milk, for example, has a less favourable P/F for cheese making than Holstein milk. This is partially offset by a higher casein number (casein as a percentage of total protein) in Jersey milk. 

Standardizing to target protein/fat ratios

Standardization normally means adding skim milk or skim milk solids, or removing cream to increase the ratio of protein to fat (P/F). Several practical points are relevant.

• Multiple component pricing makes it possible to cost milk components as individual ingredients. P/F can then be optimized according to relative costs of protein and fat, transfer rates of protein and fat from milk to cheese, and the value of fat in the cheese relative to its value as cream.
• Component yield economies must be balanced against cheese quality.
• Calculation of P/F to produce cheese with required moisture and fat depends on retention of fat, casein and serum solids in the cheese, where serum solids refers to recovery of the soluble components of milk, namely, sugars, whey proteins, nonprotein nitrogen and some minerals. Specifically the important principles with respect to serum solids are:
  • Higher serum solids recovery means that a lower P/F is required (that is more fat or less protein) in the cheese milk to achieve the target FDM in the cheese.
  • Serum solids recovery is increased in high moisture cheese because the moisture retained includes dissolved solids.
  • Serum solids recovery is reduced by curd washing treatments.
  • Serum protein (whey protein) recovery is increased by milk pasteurization (there is more discussion on heat treatments in the next section).

Standardizing to casein/fat ratios

Better process and composition control can be achieved by standardizing to fixed casein/fat ratios rather than protein/fat ratios. This requires accurate casein measurement which is still not feasible for most plants. See further discussion in Standardization of milk for cheese making and Yield efficiency. 

Sources of milk proteins

Standardization usually requires the addition of protein or removal of fat. The former has the advantage that it is possible to produce cheese quantities beyond what's possible from the available fresh milk. This is significant in areas where fresh milk is in short supply or as in Canada, where milk purchases are limited by quotas. Several sources of milk proteins are available for cheese milk standardization. 

(1) Skim milk powder is convenient for small or remote cheese plants. It can be used effectively with the following limitations:

• Use only certified LOW HEAT (Whey Protein Index > 6) and antibiotic free powders.
• Reconstitute the powder thoroughly and filter to remove undissolved particles before blending with the cheese milk. Incomplete solubilization may cause over set Swiss cheese and poor stretching of pasta filata cheese.
• Nonfat solids of cheese milk should not be raised above about 11% (normal level is 9%). This can be avoided by adding more water with the powder.
• Protein from skim milk powder is usually more expensive than from other sources.

(2) Skim milk and condensed milk are convenient sources because they can be handled and measured in liquid form. The only cautions are to limit heat treatment to minimum pasteurization requirements and limit nonfat milk solids to less than 11 kg/100 kg. Again, nonfat solids can be adjusted by adding water. 

(3) Culture media contribute nonfat milk solids which must be accounted for in calculations for milk standardization. For example, the high heat treatment involved in bulk culture preparation ensures that most milk proteins (including whey proteins) present in the culture will be transferred to the cheese. 

(4) Protein concentrates and isolates available to supplement cheese milk are numerous. A few are listed below. The feasibility of using one or more of these products, depends on, among other things, the type of cheese. For example, relative to most other varieties, high levels of whey proteins can be used in Feta cheese without compromising quality.

• Liquid or dried milk concentrates prepared by ultra filtration of skim milk contain caseins and whey proteins in the normal proportions found in milk.
• Specially prepared blends of caseins and whey proteins.
• Liquid or dried casein concentrates prepared by microfiltration of skim milk.
• Liquid concentrates of denatured whey proteins.

Sources of milk fat

Most jurisdictions prohibit the use of non dairy fat in cheese. That leaves a number of choices:

• Milk and cream unaltered other than by pasteurization and gravity or centrifugal creaming.
• Recombined cream prepared from skim milk and butter oil. This process requires homogenization which is generally considered undesirable with some exceptions including Feta, Blue and cream cheese. According to some recent work quality problems associated with homogenization can be eliminated by homogenizing the cream rather than the milk. Homogenization of cheese milk is further discussed in Section 5.4 below.

In cases where nondairy cream is desirable, the limitations are:

• Altered flavour, especially the absence of short chain fatty acids such as butyric which are only found in dairy fat. The flavour problem can be addressed by dairy flavour additives.
• Preparation of filled cheese milk (filled means containing fat other than dairy fat) requires homogenization, which as noted normally creates inferior texture.
• The fat should have melting properties similar to butter fat.

Manual standardization

In the absence of online systems equipped with customized algorithms, it is necessary to create spread sheets to calculate milk formulae and monitor yield parameters. The first step is to determine the optimum P/F, a process that always involves some experimentation. The estimates given in Table 6.1 can be used for a first approximation and then adjustments can be made on succeeding days based on the cheese analysis. This emphasizes the need for consistent and accurate records of milk and cheese composition and manufacturing parameters.

Detailed procedures, including calculations, for manual standardization are described in Standardization of milk for cheese making.

Automated standardization

Automated composition control systems separate warm milk into cream and skim and then automatically and continuously recombine the two streams in the proportion required to obtain the desired P/F ratio. The standardized milk is tempered to the correct setting temperature and delivered directly to the setting vats. Two general types of control are possible.

• Fully automated using online milk analysers based on near infra red or light scattering technology.
• Partially automated control where composition is monitored with an in line density metre which is calibrated using an off line milk analyser.

Recombined Milk

Considering the limitations described above for protein and fat sources, it is possible to manufacture cheese from recombined milk.

Failure to achieve optimum standardization for maximum yield efficiency is a major cause of economic loss in many cheese plants.

Table 6.1.  Some cheese varieties with some characteristics, composition and suggested ratio of protein/fat in standardized  milk.  Fat and moisture levels for most varieties correspond to definitions given in Canadian regulations.

 

CONSTANTS,  ASSUMPTIONS AND LEGEND

1.  All cheese composition and yield values are in units of percent by weight--including both cheese and standardized milk.

2.  Estimation of yield and protein/fat ratios are based on principles and yield equations described by D.B. Emmons, C.A. Ernstrom, C. Lacrois and P. Verret.  J. Dairy Science 73(1990):1365.

3.  Calculations based on fresh milk of 3.90% fat and 3.20% protein and assuming standarization was by removing 35% cream from the same fresh milk

4.  Whey solids in moisture was assumed to be 6.5% except for washed types when a value of 3.2% was used.  For the purpose of yield calculations, pasta filata types (hot stretch) were considered to be unwashed.  75% of cheese moisture was considered available as a solvent for whey solids.

5.  Conversion factors:

Proportion of fat transferred from milk to cheese was   0.93

Amount of casein + minerals transferred to cheese was  casein x 1.018

Casein number was 76.5

Washing: 

'warm' means washing at temperatures near normal cooking temperatures (32-40^oC)

'cold'  means wash water at  temperature less than 20⁰C is used to wash and cool the curd

'maybe warm'   means that the cheese may or may not be washed with warm water

'hot stretch' means the cheese is heated and worked in hot water (70-80⁰C) as in Pasta Filata types.

Salting:  B = brine salted;  DS = dry salted on cheese surface;  DC = curd dry salted before hooping.

FDM = fat as percentage by weight of cheese solids;    MNFS = moisture as percentage of non-fat substance in cheese.

Prot/Fat  = ratio of protein to fat in standardized cheese milk.

See also Pasteurization in the Dairy Science and Technology Education website.

Many people assume that all dairy products in Canada, including cheese, are made from pasteurized milk. Not so; several alternatives are possible as outlined below. Note, however, that the Food and Drugs Act and Regulations, recognizes only two types of cheese with respect to milk heat treatment, namely, fully pasteurized milk and raw milk. That is, if the milk is not fully pasteurized the resulting cheese is considered raw milk cheese. 

1. No heat treatment results in raw milk cheese which has more flavour. Raw milk cheese by law must be "held at 20C or more for a period of 60 days or more from the date of the beginning of the manufacturing process, " Food And Drugs Act And Regulations, Sections B.08.030 and B.08.043. The question of raw milk cheese is an ongoing concern to consumer groups and to health authorities. Suffice it to say that with respect to regulations on cheese milk heat treatments, 'one size doesn't fit all'.

2. Thermisation (63-65C, short hold) results in phosphatase positive milk which must be fully pasteurized before cheese making. The purpose is to prevent raw milk spoilage (eg. over a weekend) due to acid or protease producing bacteria.

3. Pasteurization (63C, 30 min. or 72C, 16 s) is generally considered the safest alternative, but the full flavour of traditional ripened cheese can not be achieved. Note that over pasteurization causes denaturation of whey proteins which subsequently adsorb to the casein particles. The effects are:

• Longer flocculation times
• Weak or no curd formation
• Excessive loss of fines
• Poor syneresis (moisture release)
• Coarse textured curd with reduced ability to stretch, mat and melt.

4. Heat treat (55 - 65C, 16 s) is trade lingo for subpasteurization treatment which is applied to destroy most pathogens but allow some bacteria to survive and contribute to cheese ripening. This process permits fuller flavour of cheese with better control of culture growth (i.e., acid development) than with raw milk. For current regulatory purposes, heat treat is equivalent to raw. Most aged Canadian Cheddar is safely made from heat treated milk

See also Homogenization in the Dairy Science and Technology Education website.

The process of homogenization reduces milk fat globule sizes from 1 - 15 micrometer to less than 2 micrometer (a micometer is 0.000,0001 m). The natural membrane on the fat globule is replaced by milk proteins, mainly caseins. This results in increased interaction between fat globules and the casein particles in the rennet gel. For some cheese homogenization is desirable:

• Homogenization promotes lipolysis, whitening, and flavour development in cheese made from cows' milk but which are traditionally made from goats' or sheep's milk, e.g., Blue and Feta.
• Homogenization increases fat recovery and creates smoother texture in cream cheese.

With respect to most firm to hard ripened cheese, many workers have observed that cheese made from homogenized milk are too tough and firm after pressing. However, there is evidence that homogenization for Cheddar cheese making has some advantages if medium pressure (6.9 MPa) is used and if only cream (35% fat) is homogenized and subsequently blended with unhomogenized skim milk (Nair et al. 2001, Int. Dairy Journal 10:647).

• Increased rate of gel firming and higher curd firmness at cutting.
• Increased cheese yield due to greater moisture retention and improved fat and protein recovery.
• Notwithstanding higher moisture content, cheese texture and flavour was not decreased by homogenization.

(1) Calcium Chloride is frequently added at a level of about 0.02% to aid coagulation and reduce amount of rennet required, especially if milk is set immediately after pasteurization. The role of calcium in milk coagulation will be discussed in Coagulation. 

(2) Nitrates (sodium or potassium nitrate) be added at levels of about 200 ppm to Edam, Gouda, Swiss to inhibit growth of gas forming Clostridium tyrobutyricum. 

(3) Annatto cheese color is added to some cheese to standardize seasonal changes in color or to create orange cheese such as Cheddar and Cheshire.

 The following are some facts about annatto.

• Annatto is a carotenoid similar to -carotene and Vitamin A in structure, but it has no Vitamin A activity.
• Annatto color is red to yellow pigment but it usually appears as orange. The red constituent is more apparent with decreasing pH (6-4.8) changing the orange to pink while at pH < 4.8 the pink fades and becomes nearly white. This explains the phenomenon of 'acid-cut cheese'.
• Bleaching and pinking of annatto is also caused by oxidizing agents such as copper, iron, chlorine and light.
• Oxidation of annatto is also encouraged by heat, so annatto is an unsuitable colorant for process cheese
• Alternatives to annatto are:
  • Beta-carotene which is too yellow and makes the cheese taste like carrots.
  • Apo-8-carotenal which has the advantage that it is not lost in the whey.

Decolorants

Goats' and sheeps' milk are flat white in color because they lack -carotene. Cows' milk may be whitened to mimic goats' or sheeps' milk. Chlorophyll based products which mask the natural yellow colour can be used as whitening agents. Titanium dioxide is an effective whitening agent but is no longer a legal additive for cheese. 

(5) Ripening Agents

A wide range of products are available to accelerate cheese ripening or to develop a broader flavour profile. Relative to traditional cheese varieties, several factors suggest the need for ripening supplements:

• Nontraditional cheese making methods
  • Pasteurized or heat treat versus raw milk
  • Cows' milk substituted for the milk of other species
  • Traditional rennet pastes containing a wide range of enzymes including lipases and proteases have been replaced with purified extracts
  • Cold storage and transport of milk severely alters natural milk micro flora
• Economic pressure to reduce ripening time
• Marketing pressure to standardize quality attributes

Lipases (lipolytic enzymes) are traditionally added to cows' milk to produce cheese such as Feta, Romano, Kefalotyri, and Parmesan which are traditionally made from goats' or sheeps' milk. That's because goats' and sheep's milk, especially goats' milk, have more natural lipase than cows' milk. Commercial lipases are commonly extracted from kid goats. 

Enzyme Cocktails

Mixtures of enzymes from various sources added to the milk to accelerate ripening of aged cheese such as Cheddar. These cocktails include both lipases and proteases, with a predominance of proteases for Cheddar. Bacterial enzyme extracts from lactic acid bacteria have also been used. Accelerated ripening is further discussed in Ripening and packaging.

Standardization of cheese milk normally requires increasing the proportion of protein relative to fat, which can be done by adding protein or taking away fat. The relative amount of protein and fat in milk is called the protein-fat ratio or P/F. The P/F is the principal factor which determines the amount of fat in the cheese relative to other milk solids in the cheese. Because it is easy to measure cheese fat and total solids, the proportion of fat in the cheese is reported as (1) fat on a wet basis; and (2) the ratio of cheese fat to cheese total solids. This ratio is called 'fat in the dry matter' or F/DM. The F/DM in cheese is determined mainly by P/F of the milk but the percent moisture is also important. Because cheese whey contains soluble solids, higher cheese moisture means that more soluble solids (mostly non-fat solids) are also retained in the cheese so that the ratio of F/DM decreases. The target value of F/DM in the cheese is used to determine the first approximation of the P/F required in the milk to give the desired fat content of the cheese. 

There is a third ratio, namely, casein number (CN), which we will use in the standardization procedures given below, but which is important to understand. Total protein content of cows' milk is about 3.3Kg/hL of which about 2.6 /Kg/hL is casein. The remainder is whey protein (about .7 Kg/hL) including about .1 Kg/hL of some nitrogenous compounds which are not true protein and are referred to collectively as non-protein nitrogen (NPN). Casein is mostly recovered in cheese (i.e., transferred from milk to cheese during cheese manufacture). Whey proteins remain soluble in whey so that only small amounts are recovered depending on how much whey is retained in the cheese. Casein content is, therefore, most relevant to cheese yield, so when cheese makers standardize milk on the basis of protein content, they are using total protein as an index of casein content. Direct measurement of casein would be better because the proportion of casein in total protein varies with breed, season, region and other factors. However, wet chemical analysis of casein is not feasible for most plants and rapid instrumental methods are still under development.

The percentage proportion of casein in total protein is referred to as the casein number (CN). 

There are three methods of standardizing milk, namely:

1. Addition of concentrated non-fat milk solids (i.e., skim milk powder or condensed skim).
2. Addition of skim milk.
3. Removal of cream.

These methods are based on the assumption that the milk has a high fat content relative to the protein content. This is normally the case, so that cows' milk usually has excess fat over that required to produce a legal cheese. The exceptions are high fat cheese such as cream cheese or double cream blue cheese.

It is not always economical to standardize milk. The cheese maker must compare the costs of standardizing with the extra yield of cheese or cream. Many cheese makers simplistically assume that all they have to do is standardize milk to meet the official composition standards. But the objective of standardization is to maximize the total return from all milk components while meeting regulations and without compromising quality. If the value of butter fat is low relative to protein, it is more economical to sell the fat as cheese rather than as cream provided that the extra fat can be retained in the cheese without compromising quality.

Raw milk composition for payment purposes is reported in units of Kg of component per hL of milk at 4C. This is referred to as weight over volume (w/v) measurement. Measurement in units of w/v is dependent on milk density which in turn is affected by both composition and temperature. Weight over weight (w/w) measurement (eg., Kg component per 100 Kg of milk) results in a significantly smaller value because the density of milk is more than 1 Kg/L. Measurement by w/w has the advantages that: (1) most wet chemical reference analyses used to calibrate milk analysers report composition in units of w/w; (2) w/w values are independent of milk temperature. However, milk composition for payment purposes is reported in units of w/v because the volume of milk is easily measured with dip sticks or volumetric meters. Weight measurement would require installation of farm bulk tanks on expensive load cells. Volume rather than weight measurement of milk and other liquids is also more convenient in the plant.

In any case, the important point with respect to accurate standardization is to ensure that all measurements and calculations use the correct units. When component estimates are given as percentages, the basis of measurement must be stated as w/w percent (eg., Kg fat per 100 Kg milk) or w/v percent (eg., Kg fat/hL of milk). In this manual composition values given in percent always mean w/w. Cheese composition will always be stated in percent w/w (eg., 30% fat in Cheddar cheese means 300 g fat per Kg cheese). Similarly, 3.3 % fat in milk means 3.3 Kg fat per 100 Kg milk. If weight over volume units are used I will always state the specific units, eg., 3.3 Kg/hL. Because composition of producer milk is reported to processors in units of Kg/hL and because milk metering systems are volumetric, I will usually report milk composition in units of Kg/hL.

It is important to ensure that milk analysers are calibrated in the appropriate units and the correct units are subsequently used for milk standardization calculations and calibration of automated standardizing systems. Wet chemical analysis is normally done by weight, so reference results for milks used to calibrate milk analysers are normally reported in units of percent by weight and it is convenient to calibrate milk analysers in percent by weight (eg., Kg/100 Kg). If required, w/v values can be estimated using the following equation.

w/v=w/w x pT where pT is density at temperature T

Note, that the density must be known at the given temperature. For example, if the milk composition was given in units of w/w and you are metering milk into your cheese vat at 32C you need to know the density of the milk at 32C. For milk of average composition (4.0 % fat), the density can be estimated according to the following equation(1).

pT = 1.0366 - .00035T where pT is density at temperature T

Density values for milk of average composition (4% fat) at some temperatures relevant to cheese manufacture are:

The following steps are required to calculate the amount of powder or skim milk to be added, or the amount of cream to be removed. Suppose a cheese maker wishes to fill a 10,000 l (100 hl) setting vat for the manufacture of Cheddar cheese.

Step 1. Determine the protein and fat contents of the milk using an automatic milk analyzer. If a milk analyser is not available the protein content of pooled milk can be crudely estimated from the fat content using the following formula:

Kg/hL of protein = (0.4518 x Kg/hL of fat) + l.521

For the purpose of this example, assume the available milk contains 3.50 Kg/hL of fat and 3.l0 Kg/hL of protein.

Step 2. Determine the required fat, moisture and F/DM of Cheddar cheese. 'Dairy Products Regulations' of the Canada Agricultural Products Standards Act require Cheddar cheese to contain a minimum of 31% fat and a maximum of 39% moisture. Therefore,

FDM = % fat/% dry matter = 30.0/(100.0 - 39.0) = 49.2%

Step 3. Determine the required P/F of the milk. The P/F required to yield F/DM = 50% as required for Cheddar cheese is about 0.96.

Step 4. Calculate the amount of: skim milk powder to be added; or fat to be removed; or skim milk to be added.

Standardization by Adding skim milk powder

(i) Calculate the % protein required to give P/F = 0.96

The required level of protein = 0.96 x % fat = 0.96 x 3.50 = 3.36

(ii) The % protein to be added = 3.36 - 3.10 = 0.26 Kg/hL

(iii) Calculate the weight of protein which must be added per 100.00 hL of milk.

The required weight of protein = 0.26 Kg/hL x 100 hL = 26.0 Kg

(iv) Calculate the amount of powder which must be added assuming the skim milk powder (SMP) contains 35.0% protein. If possible the skim powder should be analyzed so the exact protein content is known. The supplier may be able to provide this information. Protein content can also be estimated using a milk analyzer to test the reconstituted skim milk.

Required amount of powder = 26.0 Kg/0.35 = 74.3 Kg

(v) Check calculations:

Weight of fat in milk: 3.50 Kg/hL x 100.00 hL = 350.0 Kg.
Weight of protein in milk: 3.10 Kg/hL x 100.00 hL = 310.0 Kg
Weight of protein in SMP: 0.35 Kg/Kg x 74.0 Kg = 26.0 Kg
Total Protein: 310.0 Kg + 26.0 Kg = 336.0 Kg
P/F ratio of standardized milk: 336.0 Kg/350.0 Kg = 0.96 

Standardization by Removing fat

(i) Calculate the level of fat required to give P/F = 0.96.

The required level of fat = Kg/hL of protein/.96 = 3.10 Kg/hL/.96 = 3.23 Kg/hL

(ii) Use a Pearson's square to calculate the litres of cream that must be removed, assuming that the separator removes cream containing 30.00 kg/hl of fat.

This means that the required proportions of cream and fresh milk are 0.27 and 26.77 parts, respectively, for a total of 0.27 + 26.77 = 27.04 parts. On a percent basis, the components are:

(iii) Calculate how much cream must be removed from 10,000 Kg of milk to provide standardized milk containing 3.23% fat. 

Cream to be removed = 1.00% of 100 hL = 1.00 hL.

(iv) Check calculations:

(v) Adjust the final weight for the quantity of cream removed. If you wish to fill the vat completely sum the vat capacity and the initial estimate of the cream to be removed and recalculate the required amount of cream.

Standardization by Adding skim milk

The following calculation is based on the assumption that the protein content of the skim milk is the same as the protein content in the skim portion of the fresh milk to be standardized. This is exactly true only when the skim milk is derived from the same source as the fresh milk.

(i) Use a Pearson square to determine the relative proportions of skim milk and milk required to yield a fat content of 3.23% as calculated in Step B above. 

This means that 0.27 parts of skim are required for 3.13 parts of milk where the total mixture consists of 0.27 + 3.13 = 3.40 parts. On a percent basis, the mixture is: 

(ii) Calculate the amount of skim and fresh milk required. 

(iii) Check:

The natural P/F of milk is higher in low fat milk. In practice, this means that when the milk fat is less than 3.0%, it may be necessary to add fat to obtain P/F = 0.96 and make a full fat cheese with F/DM = 50%. When the required F/DM is less than 50%, it is unlikely that fat would have to be added to the milk. The natural P/F is also high in the fall and early winter so fat may have to be added for full fat cheese at these times. Some cheese such as double cream Blue or double cream Havarti may also require addition of fat. Given the fat content of available cream, a Pearson's square can be used to calculate the amount of cream required in a similar manner to the examples given above.

• Determine the fat and protein content of milk accurately and daily.
• Measure milk volume or weight accurately and keep accurate records. 
• If powder is being added, use only high quality, low temperature, antibiotic free powder of known protein content. Low temperature powder is required to ensure that excessive denaturation of whey proteins in the powder will not impair milk coagulation and/or cause texture defects in the cheese. To ensure low temperature powder, ask your supplier to certify a whey protein nitrogen index (WPI) greater than 6.0. 
• Weigh accurately the weight of powder or skim milk added or the weight of cream to be removed. 
• Determine the composition of the standardized cheese and if necessary adjust the proportions of fat and protein in the cheese milk on succeeding days. 
• If bulk starter is being added reduce the amount of protein added by the amount of protein in the culture. 
• The maximum recommended level of skim milk solids in cheese milk is 11%. Normal milk contains about 9% skim solids so the maximum level of additional skim solids is 2%. If standardization requires more it is recommended to standardize by removing fat or adding skim milk rather than by adding skim milk powder. Another alternative is to add some powder and then complete standardization by removing cream or adding skim milk. 
• Without sophisticated metering equipment it is difficult to obtain exact standardization. Provided you have a milk analyser, you can do a final check of milk composition after the milk is in the vat and then 'fine tune' the P/F ratio by adding skim solids or cream as required. 
• It is not possible to predict the exact composition of the finished cheese. However, when manufacturing conditions and milk composition are the same from day to day, it is possible to predict the composition of cheese with greater accuracy and the proportions of fat and protein in the cheese milk can then be 'fine-tuned' accordingly. It is, therefore, important to keep accurate records. 
• Be careful to use the correct units when calculating and weighing and metering. 

Lactic acid bacteria and other microorganisms are present as 'contaminants' in cheese milk and further environmental contamination takes place during cheese manufacture. Provided the milk is not chilled, it is possible to make cheese without any additional cultures, but normal practice is to add domestic cultures for the manufacture of cheese from both raw and pasteurized milk. Culture, then, refers to prepared inocula of bacteria, yeast and moulds which are added to cheese milk and cheese. In the broadest terms cultures have two purposes in cheese making: (1) to develop acidity; and (2) to promote ripening. Lactic acid cultures contribute to both of these functions, while numerous special or secondary cultures are added to help with the second function.

Development of Acidity

Raw milk at warm temperature will support a variety of micro-organisms in succession as the pH changes over time (see illustration on the right). In controlled conversion of milk to fermented dairy products, a primary component of fermentation is development of acidity by lactic acid bacteria. Acid development in cheese making is absolutely essential to cheese flavour, cheese texture and cheese safety. Acid is required to:

• Assist coagulation. Lower pH results in faster coagulation and in acid coagulated cheese is the only factor which induces coagulation.
• Promote syneresis. This is a most critical means of controlling moisture content. Acidity (specifically reduced pH) causes the protein matrix in the curd to contract and squeeze out moisture. That process of contraction is called syneresis.
• Prevent growth of pathogenic and spoilage bacteria. Proper rate and extent of acid development is the most important principle with respect to quality and safety of natural cheese. I would argue that with the exception of noncultured cheese varieties such as ricotta, proper culture growth and acid development is equal in importance to pasteurization with respect to safety.
• Develop cheese texture, flavour and colour. The following general associations are relevant to most cheese varieties.
  • high pH produces soft, soapy, fruity and bitter cheese
  • low pH produces cheese with brittle texture and mottled colour

Assist curing

• Growth factors produced by lactic cultures are required for other non-starter microorganisms which contribute to the desired flavour and body of cheese
• Enzymes (both lipases and proteases) produced by lactic cultures contribute to interior ripening of cheese and are important to both flavour and texture development.
• Special or secondary cultures are responsible for eye development, surface ripening etc. See Section 7.5.

Lactic acid cultures are often called starters or referred to by the acronym 'LAB' which stands for lactic acid bacteria. The following lists identify and briefly describe some properties of LAB. LAB are:

• Non-motile gram+ bacteria
• Non spore forming
• Catalase and nitrate negative
• Micro-aerophilic which means they tolerate only low oxygen concentrations
• Not psychrotrophic which means that cold storage rapidly depletes their numbers and encourages the growth of spoilage bacteria as described in Raw milk quality.
• Cocci (spherical cells) 1 µm in diameter OR rods (rod shaped cells) 1 µm wide and 2 to 3 µm long.

Classification of lactic cultures, is confusing, because many LAB have been renamed. Table 7.1 lists the old and new Latin names for some common lactic cultures.

It is helpful to categorize lactic cultures according to general technological and growth characteristics. From that perspective, LAB are grouped by four criteria, namely:

• Principal metabolites (end products of fermentation)
• Optimum growth temperatures: meso- versus thermophilic
• Starter composition:
  • Pure defined strains
  • Mixed defined strains
  • Pure (single) strains
• Forms of inoculation

(I) Principal metabolites: homo- versus heterofermentative

Homofermentative means that lactic acid is the principal metabolite without production of gas (CO2) and flavour compounds.

Heterofermentative means that lactic acid is the principal end product of fermentation but technologically significant amounts of one or more of the following metabolites are also produced.

• Carbon dioxide (CO2 ) which causes the small gas holes in Havarti, Gouda and other cheeses. Gasiness in most cheese varieties is a defect.
• Short chain fatty acids such as acetic acid and propionic
• Acetaldehyde, a principal component of yoghurt flavour
• Diacetyl, a principal flavour note in sour cream, butter milk, Dutch cheese and Havarti cheese
• Ethyl alcohol

(II) Optimum growth temperatures: meso- versus thermophilic

Mesophilic cultures as the name implies prefer medium range temperatures, rather than cold temperatures (psychrophilic) or hot temperatures (thermophilic).

• Optimum growth range for mesophyllic cultures is 30 - 35C.
• Acid production is slow or absent at temperatures less than 20C.
• Growth is inhibited at temperatures greater than 39C.
• Generally any cheese which does not require high temperatures to dry the curd will utilize mesophilic cultures. These include Cheddar, soft ripened cheese, most fresh cheese, and most washed cheese.
• Include both homo- and heterofermentative cultues 

Thermophilic cultures are defined by their ability to grow at temperatures above 40C. With respect to cheese making their important characteristics are:

• Optimum growth in the range of 39-50C
• Survive 55C or higher
• Minimum growth temperature is about 20C below which cell counts decrease rapidly, so, bulk thermophilic cultures should not be stored at temperatures <20C.
• Thermophilic starters are normally mixtures of cocci and rod cultures which at the time of inoculation are about equal in numbers. That is, the initial inoculum is 50% cocci and 50% rods.
• Rod/cocci blends grow together in a relationship referred to as 'mutualism' where the overall growth rate and acid production is faster than either culture on its own. The rods produce amino acids and peptides which stimulate the growth of cocci, and the cocci produce formic acid which is required by rods.
• The balance between the rods and cocci can be controlled by temperature and pH
  • The cocci prefer higher temperatures (optimum about 46C) than the rods (optimum about 39C).
  • The rods are more acid tolerant than the cocci, so, normally the cocci develop the initial acidity and out grow the rods. But, as the acidity increases the rods begin to grow faster than the cocci.
• Some thermophilic rod cultures have the ability to ferment galactose as well as glucose which is desirable in some cheese, especially Mozzarella.
• Although yoghurt cultures which include both rod and cocci, produce acetaldehyde which is the principal component of the characteristic yoghurt flavour, none of the thermophilic LAB are considered heterofermentative 

(III) Starter composition:

• Pure defined cultures are single strain cultures selected from natural mixed populations for specific properties such as proteolytic characteristics or resistance to phage (bacterial viruses).
  • May be rotated to avoid phage infection
  • Have the advantages of uniform rate of acid development and uniform flavour profiles
• A mixed defined culture is a blend of single strain cultures.
  • May be rotated to avoid phage infection
  • Has the advantages of uniform rate of acid development and uniform flavour profiles
• Mixed cultures are nonspecific blends of cultures, some what like a natural eco system
  • Normally have complex systems of phage resistance
  • Mixed mesophilic starters are still common, but thermophilic starters are usually mixed defined cultures.
  • Disadvantage is nonuniform rates of acid development from vat to vat and nonuniform flavour profiles.

(IV) Forms of Inoculation

Cultures can be carried and prepared for cheese milk inoculation in one of three general formats:

• Traditional starters which need several scale up transfers. This system requires some microbiological facilities and expertise and is only feasible for very large plants or perhaps for smaller plants which use mixed strain cultures.
• Bulk set culture. In this system, the culture supplier does all the purification and transfer work, and delivers a bulk set culture which is used to inoculate a bulk culture, which in turn is used to inoculate the cheese milk. Bulk cultures are the norm in medium to large plants because the cost savings are significant.
• Direct to the vat cultures require no scale up at the cheese plant. Concentrated cultures ready to inoculate the cheese milk are supplied directly by the culture supplier. 

Table 7.1: Some lactic acid bacteria commonly used in cheese making.

 

In addition to properties mentioned above, the following lists includes other technological properties of importance to cheese making. Note that many of these technological characteristics are encoded on extra-chromosomal genetic material called plasmids. Plasmids have the disadvantage of being unstable so characteristics encoded on plasmids are also unstable. The advantage is that plasmids can be transferred to other bacteria so microbiologists can readily transfer technological properties from one LAB to another.

• Lactose metabolism. Most but not all LAB are able to metabolize lactose.
• Galactose metabolism. The ability to ferment lactose is important for late acid development in Italian cheese and to control browning on Mozzarella cheese.
• Proteolytic characteristics which determine cheese flavour development.
• Resistance to phage (bacterial viruses).
• The ability to metabolize citrate which is associated with flavour development (diacetyl or butter milk flavour) and gas formation.
• Production of bacteriocins, that is, antibiotics produced by bacteria against other bacteria.
• Resistance to bacteriocins
• Antibiotic resistance.

In addition to lactic acid cultures many special or secondary cultures are used to promote specific ripening (both flavour and texture) characteristics.

• Large holes: Propioni bacterium freudenreichii subsp. shermaniee
• White moulds: Penicillium camembertii, P. caseiocolum, and P. candidum
• Blue/green moulds: Penicillium roqueforti, Penicillium glaucum
• Smears:
  • yeasts and moulds.
  • Various coryneform bacteria including Brevibacterium linens, several species of micrococci, and several species of Staphylocci.
• Ripening adjuncts:
  • Bacterial or yeast cultures added in addition to the regular lactic acid cultures.
  • Attenuated cultures which are not intended to grow but only to contribute their enzymes.
  • Species of Lactobacilli and pediococci which are intended to grow during cheese ripening and contribute enzymes.

Commercial culture preparation

Genetic techniques offer much opportunity to develop cultures with specific technological characteristics. However, at the commercial level, culture preparation is relatively simple.

• Lactic cultures are grown in buffered media to facilitate maximum growth without acid inhibition
• The cells are concentrated by centrifugation
• The cell concentrate is fast frozen or freeze dried (lyophilized). Frozen (-40C) or lyophilized cultures can be stored for several months without substantial loss of activity. Lyophilized cultures usually require a longer "lag time", i.e. time between inoculation and rapid cell growth. 

Culture Practice in the Cheese Plant

Direct to the vat cultures need only be stored under prescribed conditions and opened and delivered to the vat under aseptic conditions. The following comments relate to the preparation of bulk culture at the cheese plant.

• Culture preparation should take place in a separate culture room which is kept at positive air pressure with hepa-filtered air (0.2 µm filter).
• All surfaces in the culture room must be of a material that can be sterilized.
• Use sterile pipettes and sanitize surfaces and equipment with 200 ppm chlorine.
• Alternative culture media are:
  • Milk, but care must be taken to avoid rancid milk, mastitic milk, milk containing antibiotics, and milk with high bacteria counts.
  • 10 -12% reconstituted skim milk powder is adequate provided that the powder is tested and certified antibiotic free.
  • Whey and reconstituted whey powder may be used, but may not achieve the same cell counts as skim milk (due to less buffer capacity).
  • A number of commercially prepared culture media are available. Most of these are based on milk protein powders.
• Culture media may be buffered with phosphates to increase cell counts but some cultures particularly Lactobacillus. bulgaricus appear to be inhibited by phosphates.
• Addition of phosphates also confers phage resistance because phosphates bind calcium, and phage require calcium to attach themselves to the bacterial cells.
• Calcium reduced skim milk powder and addition of anhydrous ammonia have also been used to inhibit phage in bulk cultures
• Culture media should be heated (at >88C for 1 h) to destroy bacteria and some inhibitory substances. Heating also reduces the redox potential (lowers oxygen concentration) which encourages the growth of LAB.
• Optimum pH endpoint before cooling is between 4.5 and 5.0. At pH less than 4.5 some cultures will pass from growth (log) phase to stationary phase and will be less active when added to the cheese vat.
• Cell count can be increased by:
  • Internal pH control using buffered media
  • External pH control by adding sodium hydroxide or ammonium hydroxide to maintain pH at 5.0 - 5.5.
• Generally cultures should be cooled to 4C after the desired minimum pH and cell counts are obtained. However, the optimum storage temperature depends on the particular culture. Consult with the culture supplier. For example, some thermophilic cultures should not be cooled below 20C. Storage time should be as short as possible, but I am aware of plants which successfully use a single bulk set culture for a week before making a new batch. 

Bacteriophage are the stuff of a cheese maker's nightmare. Like all viruses, bacteriophage (hence forth abbreviated to phage) are parasites, that is, part of their life cycle is dependent on the host bacteria. Here's a few facts about their characteristics and how they can be controlled.

• Extracellular phage, that is, phage particles existing separate from their bacterial hosts are called mature or resting particles.
• Resting particles are sperm shaped, < 1 micron in length.
• Resting particles consist entirely of DNA (genetic material) and protein. The basic construction is a DNA core enclosed in a protein sheath.
• The basic life cycle, called the lytic cycle, is:
  • The phage attaches itself to the bacterial cell wall by its tail, bores a hole in the wall with the help of enzymes and injects its DNA into the cell. The protein sheath remains outside the cell.
  • From the moment of invasion the bacteria begins to reproduce phage DNA and protein in addition to its own.
  • Nucleic acid and protein strands assemble themselves into new phage particles which eventually lyse the cell (break it open) to release the phage particles into the medium. A new generation of resting phage are now available to repeat the lytic cycle
• Sometimes infection occurs without lysis resulting in a lysogenic culture where infected cells survive and reproduce infected daughter cells. Therefore, cheese cultures can exist in one of three states with respect to phage sensitivity:

1. Insensitive due to inherent or acquired resistance.
2. Phage carrier (lysogenic). In this state the bacteria are resistant to another phage infection
3. Phage sensitive in which case the phage will grow quickly and may terminate the culture. Culture growth will stop when phage levels reach 103 to 107 per ml.

• Phage have a short latent period (reproduce as quickly as every 30 to 50 min) and a large burst size (each lysed cell will release 50 to 100 new phage).
• Phage are quite strain specific which is the reason for culture rotation. As many as 10 different cultures may be rotated on a daily basis.
• Culture failure due to phage can be recognized by normal acid development initially followed by a decrease or termination of culture growth at a later stage. This is different than inhibition due to antibiotics which can be recognized by no or slow initial growth; if inhibition is not severe, culture growth and acid development by resistant strains or mutants may increase with time.

Summary of phage control measures

• Use aseptic techniques with proper culture room.
• Rotate cultures daily and/or use defined phage resistant strains.
• Use phage resistant media for culture preparation.
• Use direct-to-vat culture to avoid contamination during transfers.
• Use a mixed strain culture of two closely related strains.
• Remove and dispose of whey daily
• Routinely check for presence of phage using a culture activity test with the culture currently in use and some whey from the most recent vat

Raw milk quality provided an introduction to milk chemistry. Now we look briefly at milk physics to help understand how milk coagulation works. Refer to the figure on the right and review the following facts:

• Milk is an emulsion with fat particles (globules) dispersed in an aqueous (watery) environment.
• The fat globules do not coalesce and form a separate layer (oil off or churn) because they are protected by a membrane layer which keeps the fat particles separate from the water phase.
• The principal group of milk proteins, the caseins, are not soluble in water and exist in milk as small particles (<300 nm) called micelles.

We can now define the following terms:

Milk: a dispersion of milk fat globules (fat particles) and casein micelles (protein particles) in a continuous phase of water, sugar (lactose), whey proteins, and minerals. 

Milk Plasma: what is left after you separate the fat globules; equivalent to skim milk for practical purposes.

Milk Serum: what is left after you take away both fat globules and casein micelles; equivalent to cheese whey for most practical purposes

Milk permeate: what is left after you take away fat globules, casein micelles, and whey proteins.

Coagulation is what happens when the casein micelles stick together. Because casein particles are hydrophobic (they hate water) their natural tendency is to aggregate (clump together). In normal milk, aggregation is prevented by two factors. If one of these factors is eliminated the micelles will aggregate and form a gel something like jello.

• The first stabilizing factor is a 'hairy' layer of surface active protein, called kappa-casein (-casein), on the surface of the micelle. This layer helps prevent the micelles from getting close enough to stick together.
• The second factor is a negative charge on the micelles. At the pH of milk the micelles are negatively charged so they repel each other.

So, basically there are two ways to coagulate milk; one is to remove the hairy layer from the micelles. That's called enzymic coagulation. The other is to neutralize the negative charge on the micelle. That can be accomplished by acidification or a combination of high temperature and acidification.

The three stages of enzymic coagulation

(1) Primary Stage

In the first stage, the enzyme (rennet) cuts off a specific fragment of one of the caseins, namely, -casein. At the natural pH of milk, about 80% of -casein must be cleaved to permit aggregation of the micelles to proceed.

(2) Secondary Stage

The next stage is the physical process of aggregation of casein particles (micelles) to form a gel. After losing its water soluble tail, -casein can no longer keep the casein particles separated, so they begin to form chains and clusters. The clusters continue to grow until they form a continuous, three dimensional network which traps water inside, and forms a gel, something like Jell-o.

(3) The third stage refers to an ongoing development of the gel network. For some cheese the gel is cut as soon as it is firm enough to do so. For others, like soft ripened cheese, cutting is delayed while the gel continues to become firmer.

Effects of processing parameters on enzymic coagulation

Because rennet coagulation takes place in stages, it is necessary to understand the effect of processing on each stage. We will focus mainly on only the first and second stages.

Effect of pH. Lower pH increases enzyme activity and neutralizes charge repulsion between micelles. Therefore, both primary and secondary stages of coagulation proceed more quickly at lower pH.

Effect of Calcium . Calcium is not required for the primary stage (i.e., enzyme hydrolysis of -casein) but is essential to aggregation of the casein micelles. At low levels of calcium the primary phase goes to completion. Subsequently, instantaneous coagulation can be induced by adding sufficient calcium chloride.

Effect of temperature. The optimum coagulation temperature for most cheese is 30-32C, the exception is Swiss which is set at 37C.

• At temperature less than 30C the gel is weak and difficult to cut without excessive yield loss due to fines.
• At temperatures less than 20C coagulation does not occur, but the primary stage goes to completion and the milk will then coagulate quickly when warmed.

Effects of heat treatments.

• Mild heat treatment such as pasteurization decreases the rate of the secondary stage. During heat treatment calcium and phosphate move from soluble to colloidal (insoluble) form, so there is less calcium available to assist with coagulation. This effect is reversed by cold storage or the addition of calcium chloride
• Heat treatment in excess of pasteurization results in increased clotting time and a weak gel. High heat treatments cause absorption of whey proteins onto the casein particles. The casein particles are then unable to form a strong gel.

Effects of Homogenization: The following effects occur if the cheese milk is homogenized in its entirety. As noted in Treatment of milk for cheese making, some of these results may be different if only the cream is homogenized and then added back to the skim milk. Homogenization primarily affects the secondary phase of aggregation. Some cheese quality effects are also noted.

• Reduced aggregation of casein particles
• Decreased syneresis
• Finer gel network due to smaller fat globules
• Improved texture of soft cheese
• Fat recovery (i.e., percent transfer from milk to cheese) is increased (Note: the same is true for acid and heat/acid coagulated cheese).
• Hard cheese becomes rubbery
• Makes cheese whiter because the yellow fat is masked by the artificial protein membranes on the homogenized fat globules.

Coagulating Enzymes

The traditional enzyme is rennet (chymosin) which is derived from the abomasum of the milk fed calf. The practice of cheese making probably began when somebody discovered that milk stored in bags made from calf stomachs formed a sweet curd.

Other proteases which have been used for cheese making include:

• Pepsins from the pig, cow and chicken
• Microbial proteases (Mucor miehi, Mucor pusillus, and Endothia parasitica).
• Synthetic chymosin by recombinant DNA techniques using strains of Eshericia coli or Klaveromyces lactis or Aspergillus niger as host organism is now available. The transferred genetic material exists in the host cell in the form of a plasmid and is used as a template for the production of an enzyme identical to chymosin.

Figure 8.3 Manufacture of chymosin (calf rennet) and fermentation produced recombinant chymosin

Requirements of suitable coagulating enzymes

• Suitable ratio of clotting to proteolytic activity (C/P). This ratio is dependent on the specificity of the enzyme for the Phe105-Met106 bond of -casein. Most rennet substitutes are more proteolytic than rennet (i.e., low C/P) and cause diminished yields of casein and fat, and bitterness during ripening
• Proteolytic specificity. Structure and flavour of ripened cheese depends on the type of proteolysis caused by the coagulant during cheese curing. The exception is in cheese such as Swiss or Parmesan where most of the rennet activity is destroyed by the high cooking temperature. During ripening chymosin breaks down one of the caseins, namely s1-casein much more than other caseins.
• High pH optimum. Rennet activity is stable and able to coagulate milk at the normal pH of milk although its activity increases with decreasing pH. Most pepsins and microbial proteases are denatured at the pH of milk which has been a major difficulty in developing rennet substitutes.
• Denaturation temperature is important for two reasons:
  • Ripening due to coagulating enzymes is not desirable in cooked cheese such as Swiss and Italian types. Rennet is eliminated during the high temperature cook in these cheeses but microbial coagulants are not.
  • The coagulant must be eliminated by pasteurization to prevent proteolysis in products made from whey. Some microbial rennets survive pasteurization.
• Distribution between curd and whey. Only 0-15% of rennet remains in the curd, but small amounts of residual rennet are significant to ripening of aged cheese. The most important factors which determine rennet retention are:
• Cooking treatments.
  • As noted above, rennet does not survive in high temperature cooked cheese varieties.
  • In low cooked cheese such as Cheddar, variations in cooking temperature and time influence rennet activity during aging.
• The pH at draining. Rennet is more soluble at low pH and, therefore, the amount retained in the curd increases with decreasing pH at draining. Retention of microbial rennets in the curd is independent of pH at draining.
• Changing rennet sources may also influence rennet retention and cheese ripening. Different rennets with the same coagulating properties may have different thermal tolerances and different proteolytic characteristics.
• Standard and consistent activity. Single strength rennet is standardized so that 200 ml coagulates 1,000 kg of milk in 30 - 40 min. Typical commercial rennet preparations are about 50% chymosin (calf rennet) and 50% bovine pepsin, so there is much opportunity for variation. Commercial calf rennet preparations are about 94-96% chymosin. Using recombinant rennet it should be possible to produce commercial rennet preparations which are more consistent with respect to all of the properties listed above, including proteolytic specificity and heat tolerance. 

Acid milk gels can be formed by lactic bacteria or the use of acidifying agents such as glucono-delta-lactone (GDL is slowly hydrolysed to gluconic acid in the presence of water). Acid coagulation is used in the production of cottage cheese, bakers cheese and quark as well as other fermented milk products such as yoghurt, commercial butter milk, kefir etc. In the case of cottage cheese and quark a small amount of chymosin may be used (2 ml/1,000 hl) to make the curd more elastic and less subject to breakage (dusting).

This process permits recovery of caseins and whey proteins in a single step. The basic principle is that whey proteins which are normally acid stable, become sensitive to acid coagulation after heat treatment. This principle is exploited in the manufacture of ricotta cheese, Paneer and Channa, and in the manufacture of "co-precipitated" milk protein concentrates. The basic process for heat-acid coagulation is:

• Heat milk or milk-whey blends to at least 80C for at least five minutes to completely denature (unfold) the whey proteins and encourage association of whey proteins with casein micelles.
• Continue heating and acidify slowly with gentle agitation. The caseins and whey proteins will coagulate together and form either sinking or floating curds.

This term is a little confusing because it is also used to describe the ripening or aging of cheese. Here, ripening, refers to the practice of giving the culture time to begin acid production before the rennet is added. This is done for two reasons:

• To ensure the culture is active before the milk is renneted. It is impossible to inoculate after the milk is set. Normally, 45 - 60 min is sufficient to decrease pH by 0.01 units or increase TA by 0.005 - 0.01%
• Development of acidity aids the coagulation process, especially the secondary stage.

In some varieties such as brine brick and Swiss, low amounts of culture are used and renneting proceeds with little or no prior ripening.

Handling Rennets

• Repeatable performance depends on accurate measurement. For most varieties the quantity of rennet is selected to set the milk to a firm coagulum in 30 - 40 min. Measure the rennet accurately and monitor to ensure that coagulation rate is uniform from day to day.
• Rennet must be diluted (about 20 times) in water and well mixed when added to ensure uniform distribution.
• Use nearly the same dilution each time to improve the consistency when adding the diluted rennet to the vat.
• Watch out for chlorine. It is imperative that the dilution water contains no chlorine. Only 2 ppm of chlorine will destroy 40% of rennet activity in 3 minutes. Similarly, do not sanitize the container used for the rennet with chlorine.
• Another water quality issue is pH. Typically hard water also has pH greater than 7.0 which also decreases rennet activity.
• Finally, dilute immediately before adding the rennet to the vat. After the brined rennet is diluted in water, its activity declines quickly.

Optimizing setting parameters

• Milk preparation was discussed in Treatment of milk for cheese making. Here are the principal considerations:
  • Pasteurization temperature: higher temperatures increase yield by increased recovery of whey proteins, but a suggested maximum with respect to curd quality is 75C, 16 s.
  • Temperature history: if the milk is pasteurized and immediately sent to the setting vat, it will be necessary to adjust the mineral balance by adding calcium chloride.
• The jury on selection of coagulant always seems to be out. I tentatively suggest that microbial coagulants are not advisable for high temperature varieties for reasons of heat stability, and not advisable for other varieties unless other setting and conditions are under tight control. The preferred choices, then, are rennet and recombinant rennet.
• The amount of rennet must be carefully determined. Because rennet is costly, it is desirable to minimize its use, but this can be false economy if curd properties are compromised. Poor setting means increased losses of both fat and protein as fines.
• Temperature control must be accurate and uniform through out the vat, because both the enzyme activity and the subsequent process of micelle aggregation are extremely temperature sensitive. Inaccurate or nonuniform temperature during setting will result in local areas of under or over set curd which in turn causes loss of fines during cutting.
• Soft curd results from:
  • Over heat treatment
  • Low setting temperature
  • Homogenization
  • Colostrum or mastitic milk
• Firm curd results from:
  • High calcium
  • Low pH
  • Standardisation to high protein content.

Proper cutting is extremely important to both quality and yield. Improper cutting and handling the curd results in the loss of fines, that is, small curd particles which are not recovered in the cheese. Unlike whey fat, fat trapped in fines; is not recovered by whey cream separation. Therefore, both fat and protein losses occur when shattered curd results in fines too small to be recovered in the cheese.

Determination of curd cutting time

Both early cutting when the curd is fragile and late cutting when the curd is brittle cause losses of fines. Several means are used to determine cutting time.

• Manual testing. The curd is ready to cut if it breaks cleanly when a flat blade is inserted at 45o angle to the surface and then raised slowly.
• Several mechanical devices based on oscillating viscometry, thermal conductance and sonication have been tested experimentally.
• Some plants cut by the clock. This may be OK as long as all conditions are uniform from day to day (is that every true??) and adjustments are made for any change in milk composition or properties.
• If setting temperature is high as for Swiss types, the curd firms rapidly and cutting must begin early when curd is still somewhat soft to prevent over setting. Agitation should begin immediately to prevent matting.

Curd size

Curd size has a great influence on moisture retention. Hence, there is an obvious relationship between cheese moisture and the prescribed curd size:

• High temperature and low moisture varieties such as Italian hard cheese require the smallest curd. Cutting continues until the curd cutting is the size of rice grains.
• Medium moisture cheeses like most washed varieties and Cheddar are cut to Omega cm cubes.
• High moisture varieties like soft ripened cheese are cut with 2 cm knives or the curd is simply broken sufficiently to be dipped into forms.

Small curd size will result in greater fat and SNF recovery because large curds tend to get crushed resulting in the loss of 'fines'. Smaller curds will also dry out faster and, therefore, other factors such as cooking temperature and stirring out may have to be adjusted according to curd size.

Manual cutting

Manual cutting is done with cutting harps, made by stretching stainless steel wire over a stainless steel frame. Total cutting time should not exceed 10 minutes (preferably less than 5 minutes) because the curd is continually changing (becoming overset) during cutting. The knives should be pulled (not pushed) quickly through the curd so has to cut the curd cleanly.

Automated cutting

With mechanical knives, curd size is determined by the design of the vat and agitators, the speed of cutting (rpm) and the duration of cutting. In Double 'O' vats for Cheddar and American varieties, cutting is normally at a speed of about 4 rpm for 7 - 13 minutes, corresponding two a total of 30 to 50 revolutions. It is important that the knives are sharp and cut the curd cleanly rather than partially mashing the curd or missing some pieces altogether.

There is evidence (Johnston et al 1991, J. Dairy Res. 58:345) that curd particle size at draining in mechanized Cheddar cheese is influenced by cutting time, cutting speed, and subsequent agitation such that:

• Short cutting times and low rpm result in small particle size at draining and larger losses of fines.
• With increasing cutting time (more total revolutions), curd particle size at draining reaches a maximum which corresponds to a maximum in fat recovery.
• Further increased cutting time causes decreased curd size at draining with little effect on fat recovery.

Healing

Curd should be agitated gently or not at all after cutting to prevent formation of fines. The exterior of the freshly cut curd is fragile so some time is needed for the edges to close up (heal) and prevent the loss of fat and protein to the whey.

An index of cutting quality

The loss of fines is best monitored by accurate analysis of whey fat content. Whey fat for Cheddar types should be <0.3%;. Efficient operations may achieve levels near 0.2%.

The combination of heat and the developing acidity (decreasing pH) causes syneresis with resulting expulsion of moisture, lactose, acid, soluble minerals and salts, and whey proteins. It is important to follow the cooking schedule, closely. Cooking too quickly causes the curd to shatter more easily and forms a tough exterior on the curd particles which prevents moisture release and hinders development of a smooth texture during pressing.

Most cheese is drained in the range of whey pH 6.1-6.4 (curd pH 6.0 - 6.3). Draining time should be uniform at about 20 min to prevent variation from vat to vat. Cheddar types may be stirred out 1 to 3 times as required to obtain required curd moisture.

Lactose content can be adjusted by moisture removal (syneresis), fermentation, or leaching with water. By leaching lactose with water it is possible to make a high moisture cheese (such as brine brick or Muenster) and still achieve a final pH of about 5.0 - 5.2. The temperature of the wash water will determine the moisture content of the curd. Sometimes relatively hot water (eg., Gouda) is used to dry the curd and develop its texture.

Traditionally washing was accomplished by removing Omega to 2/3 of the whey and replacing it with water and agitating for about 15 min. This process results in the dilution of large amounts of whey which must be reconcentrated or dumped. It also creates problems where curd tables have less capacity than setting vats. The solution is to remove more whey and add less water.

Most brine or surface salted varieties are dipped directly into the forms or pressed under the whey. In the absence of salt, the curd is fused to form a smooth, plastic mass. The hoops are turned at regular intervals to promote uniform drainage, symmetrical shape, and a smooth finish.

Some varieties such as Gouda and Swiss are pressed under the whey before draining. This encourages formation of smooth texture and prevents incorporation of mechanical openings in the cheese due to trapped air or pockets of whey.

For Cheddar, American, and Pasta Filata varieties the curd is kept warm in the vat or drain table and allowed to ferment to pH 5.2 -5.4. Pasta Filata varieties are then worked in warm water while Cheddar and American varieties are salted in the vat.

Pressing varies from little or none for soft cheese up to 172 kPa for firm Cheddar cheese. The warmer the curd, the less pressure required. Mechanical openings may be reduced by vacuum treatment before, during or after pressing.

Almost all cheese is salted by one of three methods: before pressing as in Cheddar and American varieties, surface salting after pressing, or brine salting. 

Purposes of Salting

• Promote further syneresis
• Slow acid development
• Check spoilage bacteria. Lactics are more salt tolerant than pathogens and spoilage bacteria.
• Promote controlled ripening and flavour development.
• Salty flavour

Brine salting:

• Concentration 16 - 25% NaCl
• Time:

20 kg cheese, 5 days or sometimes several weeks

3-5 kg, 24 h

250 - 350 g, 1 - 4 h

• New brine should be treated with about 0.1% of CaCl2 to prevent conversion of calcium and hydrogen caseinate to sodium caseinate. The latter has high water holding capacity, so the cheese takes up water from the brine and the cheese surface becomes soft and slimy.
• Brine pH should be adjusted to the pH of the cheese. Normally a pH of 5.2 - 5.6 is adequate.
  • If the pH is too high, ion exchange causing sodium caseinate is encouraged.
  • If the pH is too low, there is insufficient Ca/Na exchange and the cheese is too hard and coarse.
• Brine must be cleaned regularly by filtration, preferably microfiltered. UV sterilization combined with filtration is also used.
• Brine must be continuously agitated to prevent density fractionation (lower concentration brine on top) and dilution of the brine around the cheese.
• If cheese is floated rather than immersed in the brine, the exposed surface of the cheese should be dry salted.

Vat salting

• For vat salted cheese, uniform salt content depends on accurate estimate of the weight of unsalted curd, accurate weighing of salt, and consistent processing conditions.
• Salt uptake is:
  • Increased by increased acidity (lower pH) at salting.
  • Decreased by increased time between milling and salting due to healing of the cut surfaces on the curd particles.
  • Increased by increased curd moisture content.
  • Decreased for larger curds.
• For Cheddar and American varieties the salt content as a percent of moisture (S/M) should be greater than 4.0%. 

Cheese ripening is basically about the breakdown of proteins, lipids and carbohydrates (acids and sugars) which releases flavour compounds and modifies cheese texture. The biochemical and biophysical processes involved have only partly been elucidated. Here we include only a few practical principles of ripening.

General Principles

• Ripening varies from nil for fresh cheese to 5 years for some hard ripened cheese. Like a good wine, a good aged cheese should get better and better with age.
• Ripening processes are broadly classified as interior and surface ripened.
  • Cheese which depend mainly on interior ripening (most hard ripened cheese such as Cheddar and Italian types) may be ripened with rind formation or may be film wrapped before curing. Having said that, I hasten to add, that traditional Italian types are always rind ripened. Cheddar and American varieties are the only ripened cheeses which (in my view) are not drastically altered by film wrapped curing.
  • Cheese which depend mainly on surface ripening include smear ripened and mould ripened
• In the broadest terms there are three sources of cheese flavour:
  • Flavours present in the original cheese milk, such as natural butter fat flavour and feed flavour.
  • Breakdown products of milk proteins, fats and sugars which are released by microbial enzymes, enzymes endogenous to milk, and enzyme additives.
  • Metabolites of starter bacteria and other microorganisms. These include products from catabolism of proteins, fats and sugars.
• Flavour and texture development are strongly dependent on:
  • pH profile
  • Composition
  • Salting
  • Temperature
  • Humidity
  • EXPERIENCE.
• As a general rule factors which increase the rate of ripening increase the risk of off flavour development, and reduce the period of time when the cheese is saleable.

Protein Breakdown (Proteolysis)

Natural degradation of protein is called 'putrefaction' and results in 'rotten potato' type odours, especially if high quality proteins such as animal proteins are involved. That's because animal proteins contain the essential sulfur amino acids. These 'putrefactive' components are also the stuff of which good flavours are made. Protein degradation during cheese curing is a directed process resulting in protein fragments with desirable flavours.

• Some off flavours associated with undesirable or excessive protein breakdown in cheese are bitter, stringent, putrid and brothy.
• Protein breakdown causes shorter body which is less rubbery, less elastic, more meltable. For example, flavour and texture development in Cheddar are mainly dependent on protein breakdown and much less dependent on fat breakdown.
• Protein breakdown involves three general types of processes:
  • Proteases break proteins into smaller peptides, some of which are flavour compounds. For example, bitter and brothy flavoured peptides are well known to occur in cheese.
  • Peptidases further break down peptides to amino acids.
  • Further catabolism of amino acids by cheese microorganisms produces aldehydes, alchohols, carboxlic acids and sulfur compounds, many of which are flavourful.
• The amino acid, tyrosine, forms crystals in aged cheese such as Parmaggiano regiano, which are readily detected on the palate.

Fat Breakdown (Lipolysis)

Dairy fat is a wonderfully rich source of flavours, because it contains an extremely diverse selection of fatty acids. In particular, butter fat is the only natural fat which is rich in short chain fatty acids. Butyric acid for example is a potent flavour compound. As with all potent flavours the trick is to add just the right amounts in balance with other flavours. Here are a few principles:

• Dairy fat without any ripening during cheese making is an important contributor to cheese flavour and texture:
  • Fresh dairy fat has the well known 'buttery' flavour associated with extremely low levels of free fatty acids.
  • Fat also acts as a flavour reservoir, so hydrophobic (fat soluble) flavours derived from protein breakdown are stored in the fat and released during mastication in the mouth.
  • Finally, fat is an important component of cheese softening and melting.
• The fat derived flavours associated with cheese ripening result from the release of fatty acids by lipolysis and further modification of fatty acids by microorganisms to other compounds.
• Varieties traditionally made from goats' milk have higher levels of lipolysis.
• Blue moulds are generally quite lipolytic

Lactose

Milk contains no starch or fibre or any sugar other than lactose so all carbohydrate compounds in cheese are derived from lactose or produced by microorganisms. Relative to fat and protein lactose contributions to flavour are minimal. Here's a few principles:

• At Day 1 following cheese manufacture most of the milk sugar has been removed in the whey by or by fermentation, that is converted to lactic acid by the cultures.
• Residual lactose depends on the type of cheese and other factors. For examples:
  • High salt in the moisture phase of Cheddar slows lactose metabolism so lactose content is .3 to .7%% at one day after manufacture and slowly declines to less than 0.1%.
  • Residual lactose in Camembert cheese is used by Penicillium camemberti so it decreases quickly, especially on the surface, when the mould begins to grow.
  • In well drained cheese such as Swiss types, lactose is completely used up in a few hours.
  • In washed cheese varieties, lactose not leached by washing is quickly used up by the culture, especially for Dutch type cheese where salting is delayed. In Colby, early vat salting reduces the rate of utilization of residual lactose.
• Many organisms, including yeasts and moulds in mould and smear ripened cheeses utilize lactate and produce various flavourful compounds.
• Calcium salts of lactic acid may form white precipitates on the surface of aged cheese.

Milk Enzymes 

• Plasmin: A milk protease which survives pasteurization and breaks down caseins during cheese ripening.
  • Particularly important in Swiss type cheese.
  • Inhibited by Beta-lactoglobulin, so it has minimal activity in cheese made from ultrafiltered milk.
• Lipoprotein lipase is the principal milk lipase
  • Inactivated by low heat treatment but is important to flavour development in raw milk cheese

Milk Coagulant

• Each milk coagulant has its own proteolytic profile (see section on coagulants).
• Purified extracts produce more consistent flavours but lack character.
• For aged cheese no enzyme other than calf rennet and recombinant calf rennet has proven fully acceptable.
• Rennet and recombinant rennet actively break down alpha-casein but do not break down beta-casein in cheese.

Lactic Cultures

• During the early days and weeks of ripening, LAB numbers decrease while the numbers of nonstarter bacteria decrease. For example, in Cheddar cheese, LAB counts reach a maximum (up to 500 million per gram) within 3-4 days and then decrease to about 20 million at 4 weeks. However, the dying cells release enzymes which continue to ripen the cheese.
• Lactic cultures contribute to proteolysed flavours but are minimally lipolytic
• Heterofermentative cultures ferment citrate as well as lactose and contribute both flavour (diacetyl) and carbon dioxide for small eye development

Secondary Cultures

• In Swiss types, carbon dioxide production by Propionibacterium is encouraged by exposure to 200C for about 3 weeks after brining and drying off in the cold room.
• For smear ripened cheese, Brevibacterium linens , coryneform bacteria, and yeasts are encouraged by high humidity (90-95%) and washing to discourage moulds
• Penicillium sp. for Camembert, Brie and Blue types require 85-90% humidity and air circulation to provide oxygen

Non-starter Microorganisms

Microorganisms present in the milk due to environmental contamination are important contributors to milk ripening. Some important facts are:

• Bulk cooling and storage of raw milk selects for cold tolerant (psychrotrophic) bacteria (see Process and quality control procedures).
• Heat treatment selects for thermal stable spore forming bacteria
• Non-starter bacteria commonly present in heat-treat Cheddar include Lactobacillus sp. and Pediococci sp.
• Many other bacteria and yeasts may be present and may or not grow depending on complex symbiotic relationships with other bacteria.
• Heat treat is really a process of standardizing the nonstarter microorganisms, namely, eliminate proteolytic psychrotrophic bacteria but retain a range of useful ripening microbial agents.
• Non-starter bacteria in cheese milk can be reduced by microfiltration.

Added Ripening Agents

Addition of lipases as noted earlier is common for Italian and other cheese varieties. The principal areas of continuing development are:

• Accelerated ripening agents for all ripened cheese, especially Cheddar
• Ripening agents for low fat cheese, again especially Cheddar.
• The principal approaches are:
  • Direct addition of single enzymes of dairy or non-dairy sources
  • Enzyme cocktails which are mixtures of proteases and lipases. Other than in the preparation of enzyme modified cheese pastes, enzyme cocktails have had limited commercial success.
  • Enzyme capsules which release trapped enzymes during ripening.
  • Attenuated (freeze shocked or heat shocked) proteolytic cultures
  • Genetically modified cultures hold lots of promise for future success.
  • Culture adjuncts such as Lactobacillus helveticus in Cheddar cheese hold much promise to replace the normal diverse microflora of raw milk.

Cheese composition is critical to yield optimization, and both flavour and texture development. This section gives some detail on several critical composition parameters, with special reference to Cheddar cheese. New Zealand export Cheddar cheese is all graded by composition analysis as indicated in Figure A on the right. Figure B on the right indicates the ranges which are typical of good Canadian Cheddar.

MNFS

• Moisture: higher moisture means faster ripening which means more potential for off flavours and over ripening.
• water activity (aw) decreases with age because ripening results in many soluble breakdown products of acids, sugars, proteins and lipids
• fresh Cheddar aw = 0.98 which is conducive to most bacteria
• aged Cheddar aw as low as 0.88 which is too low for most bacteria
• MNFS is a better index of cheese ripening potential than % moisture
• Optimum MNFS depends on expected date of maturity and curing temperatures:

examples for Cheddar: 100C, 6-7 months MNFS = 53%

100C, 3-4 months MNFS = 56%

• MNFS is controlled mainly by pH at dipping and cooking treatments. Subsequent curd treatment such as cheddaring and salting also influence MNFS
• MNFS is also influenced by FDM. Other conditions being kept constant, MNFS increases with increasing FDM, because fat inhibits syneresis.

S/M

• Determines rate of acid development during pressing and early curing and, therefore, influences the minimum pH
• Affects bacterial profile, eg., high S/M will discourage contaminating bacteria such as coliforms.
• Critical to rate of proteolysis and the type of protein derived flavours
• Acceptable range is broad (3.6 - 6.0), fortunately because S/M varies widely even within a single cheese.
• Salt uptake is affected by quantity of added salt, size of curds, moisture content of curds, and acidity

FDM

• Higher fat restricts syneresis, so MNFS tends to increase with FDM
• Fat shortens and softens cheese texture because the fat globules physically disrupt the protein matrix.
• Adjusted by milk P/F (See Treatment of milk for cheese making)

pH

• The pH profile is the single most important trouble shooting tool. Critical points are: cutting, draining, milling, 1 day and 7 days
• Most cheese including Cheddar should reach a minimum pH of 5.0 to 5.1 during the first week after manufacture; obtaining a final pH in this range is greatly helped by increased buffer capacity of milk proteins in the pH range 5.4 - 4.8.
• Factors determining the pH at one day are amount of culture, draining pH, washing, curd treatment such as cheddaring and salting.
• Draining pH is most important to cheese texture and also determines residual amounts of chymosin and plasmin in the cheese.
• pH increases with age due to release of alkaline protein fragments. This is especially true of mould ripened cheeses. Camembert pH increases from 4.6 to 7.0, especially on the surface.
• Increasing pH during curing encourages activity of both proteases and lipases.

• Cheddar types: 4 - 10C, 8-10C is the recommended range. It is desirable to initiate ripening for several weeks at 4-6C and then increase the temperature to 8 - 10C. Low temperature initially, minimizes early growth of starter and non-starter bacteria and reduces the risk of too rapid ripening and off flavour development. It also minimizes the risk of the minimum pH reaching levels below 5.0.
• Most European varieties are stored at 10 - 15C for initial ripening and then 4C until consumed.
• Surface ripened varieties are ripened at 11 - 15C. 

Surface ripened cheese also require adequate air circulation to provide sufficient oxygen for moulds and yeasts. Humidity requirements in general are:

• Washed bacterial surface ripened: 90-95%
• Fungal flora: 85-90%
• Dry rinds: 80-85

According to the type of surface characteristics, cheese treatments are grouped as follows:

• Ripened by surface moulds
• Washed rinds with out (or with little) bacterial growth, e.g., St. Paulin types.
• Washed rinds with smear, e.g., Muenster types and Oka
• Dry rinds which may be coated with oil or butter to prevent cracking and desiccation, e.g., Edam, Scamorza, and Parmesan.
• Waxes and resins which may be applied by dipping, brushing or spraying. These provide good protection but are more permeable than plastic films, so it is still desirable to maintain 85% RH to prevent drying.
• Rindless cheese which are cured in moisture and gas impermeable film or in large blocks (eg., 640 lb Cheddar)

Waxes and films may be treated with anti-mould agents such as pimaricin, sorbic acid and propionates to prevent mould growth.

• Vacuum and/or gas flush (N2 and CO2) in gas and moisture proof film are common.
• Vacuum alone is not recommended because complete evacuation of oxygen is difficult and small unsightly mould spots often appear.
• Gas flush with CO2 or blends of CO2 and N2 effectively prevent mould growth.
  • CO2 is water soluble so it is absorbed into the water of the cheese and the package becomes tight.
  • N2 which is not water soluble is useful for applications, such as shredded cheese and cheese curd, where a loose package is desired.
• High density plastic (rigid containers) are used for fresh cheese such as cottage.
• Oxygen permeable wrap such as grease proof paper and foil-laminated but unsealed wraps, are preferred for surface ripened soft cheese.

To maximize returns, the cheese maker must obtain the maximum yields which are consistent with good cheese quality. For example, water and salt are cheaper than milk fat and protein, but you can only have so much cheese moisture and salt---more on cheese yield in Yield efficiency. With respect to consistent production of high quality cheese the objectives of the cheese maker are to:

1. Develop the basic structure of the cheese.
2. Obtain cheese composition required for optimum microbial and enzyme activity during curing. Optimum composition mainly means optimum levels of moisture, fat, pH (lactic acid), minerals, and salt.

For example, the characteristic texture of Swiss cheese is largely determined at the time when the curd and whey are transferred to the press table. At this time the basic structure (i.e., the manner in which the casein micelles and fat globules are arranged) and chemical composition (especially mineral content) is already determined. You can not take Swiss curd at this stage and make Cheddar cheese. On the other hand it is possible to produce both Feta and a Brie type cheese from the same curd.

• cheese making is a process of removing moisture from a rennet coagulum or an acid coagulum consisting of fat globules (unless the milk is skimmed) and water droplets trapped in a matrix of casein micelles
• cheese is, therefore, a concentrate of milk protein and fat.
• most cheese making operations are related to this process of removing water from the milk gel by the process of syneresis
• syneresis = to contract; refers to contraction of the protein network with the resulting expulsion of water from the curd
• the water and water soluble components are literally squeezed out of the curd
• this liquid, (whey) contains water, sugar, whey proteins, lactic acid and some of the milk minerals
• the final moisture content, therefore, to a large extent determines the final pH of the cheese because it determines the residual amount of fermentable lactose in the cheese
• at the same time other factors such as the amount and rate of acid development and the temperature and time of cooking, determine the amount and the rate of syneresis

•  with respect to cheese quality and safety, the most important process control factor is the development of acidity
• increasing acidity causes:
  • syneresis (due to reduced charge repulsion on casein micelles) and moisture expulsion
  • solubilization of calcium phosphates
  • disruption of casein micelle structure with alterations in curd texture
  • reduced lactose content by fermentation to lactic acid
• acid development occurs mainly within the curd because most bacteria are trapped in the gel matrix during coagulation
• final pH (acidity) is dependent on the amount of acid developed during manufacture and the residual lactose which will ferment during early curing and cause further acid development
• the residual lactose content is mainly determined by the moisture content, washing which removes lactose by leaching, and the extent of fermentation
• ability of culture to ferment galactose is also important
• both the rate of acid development and the amount of acid development (as measured by final pH) are important
• eg., final pH of Swiss is the same as Cheddar but Cheddar cheese reaches pH 5.2 after about 5 hours while Swiss cheese requires about 15 h to reach this pH
• it is important to maintain uniform rate of acid development; if acidity develops too slow or too fast, adjust the amount of culture rather than changing cooking time or temperature
• pH at draining largely determines the mineral and residual sugar contents of the cheese and from the sugar, the final pH
• salting reduces the rate of acid development, and, therefore, the time and amount of salting is important to the pH at 1 day and 7 days following manufacture. 

• loss of calcium phosphate determines extent of casein micelle disruption--hence it determines basic cheese structure; the important parameter is the ratio of Ca to casein or Ca to SNF which is easier to measure (See Table 1.1)
• in Swiss (high Ca, about 750 mM Ca/kg SNF) micelle globular structure is intact while extensive dissociation and disruption of submicelles is evident in Feta types (low Ca, about 400 mM Ca/kg SNF))
• retention of calcium phosphate in the cheese also increases the buffer capacity of the cheese
• pH at draining determines the solubility of calcium and phosphate when the curd is separated from the whey
• more Ca is retained at high draining pH as in Swiss cheese (pH 6.4 - 6.5) versus Cheddar 6.1 - 6.3 (See Table 1.1).
• little Ca retained in Feta cheese which needs some explanation:

Feta is dipped into the forms early while the pH is still quite high. However, the moisture is also high because no cooking has taken place. Therefore, the moisture is removed by syneresis as the pH decreases while the cheese is in the forms. The net result is that a great deal of moisture (whey) is removed at low pH and most of the calcium phosphate is removed with it. This is also true for other soft ripened cheese like blue and camembert.

•  untypical texture in a young cheese is a strong indication of probable flavour defects later; therefore, a primary objective of cheese making is to develop the ultrastructure which will determine the proper texture
• conformation of the protein matrix is also influenced by pH--at lower pH micelles are disrupted, but the proteins are tightly packed because of reduced charge repulsion; therefore, Feta is brittle while Camembert is soft and smooth due to alkalinity contributed by ammonia during ripening
• cheese drained at higher pH has higher calcium content and is firmer and more elastic
• firmness is also affected by ripening agents (see 11.6 Flavour control)
• other factors also play a role--salt, moisture, and fat, but none of these will alter the basic structure of the protein matrix at the submicellar level.

• milk heating and clarification treatments which determine non-starter bacteria present in the milk
• types of cultures and coagulating enzymes
• all cooking and curd handling procedures have specific effects on the types of ripening agents (bacteria and enzymes) which remain to ripen the cheese; especially in cheese such as Swiss where the composition and functions of the culture are more complex
• pH at draining again important because it determines the distribution of plasmin and rennin between the curd and the whey
• plasmin is the principal milk protease: it prefers neutral to slightly alkaline pH and is more soluble at low pH; therefore, cheese which are dipped at high pH have higher retention and activity of plasmin (eg., in Swiss protein breakdown during ripening is due to plasmin)
• calf rennet is more soluble at higher pH but more active at lower pH; therefore, an acid cheese such as Feta or Cheshire, has more rennet activity than Cheddar
• the solubility of microbial rennets is independent of pH

The following grading description and score sheets are included as examples only. The Agriculture and Agri-Food Canada official scoring system for export Cheddar is below. Also included is a general score card entitled “Cheese Judging Score Card” that can be used for any cheese variety (Table 13.1) at the end of this unit.

Agriculture And Agri-Food Guidelines For Grading Cheddar Cheese

Standards - Canada Dairy Products Act.

 

Notes:
1. Cheese should be held overnight at 14.5 - 15.5°C before grading.
2. Cheese samples should be 9 Kg in weight.
3. Cheese should be at least 21 days old before grading.
4. Early evaluation of aging potential can be obtained by grading a sample stored at 15°C for 21 days.

Common Descriptors used in Grading Canadian Cheddar Cheese

Code - Total Score, Maximum 94

1.      Sl. open, sl. stiff, sl. coarse, blurred branding, sl. damp end, sl moldy surface.

2.      As above plus slight acid tendency.

3.      Weak, open, coarse, wet ends, sl. acid, sl. gas or pin holes, mottled colour etc.

4.      Checked rinds with mold penetration. Sl. gas or pin holes. Any above defect plus a second defect except weak and open.

5.      Very weak, very acidy, very stiff, very open, gas or Swiss holes (always 3rd), very uneven colour, very mottled.

6.      Checked rinds, mold penetration, gas or Swiss holes (always 3rd).

Code - Flavour Score, Maximum 40

F₁     Sl. unclean, sl. off, sl. fruity, sl. weak. sl. musty, sl. bitter, sl. sour.

F₂     Sl. rancid, fruity, off, bitter, weed, sour, musty.

F₃     Very fruity, rancid, badly off, very bitter, very unclean, very weedy.

Typical Example - Cheese Score

 

TABLE 12.1. Distribution of milk components during cheese making (% by weight) and percent transfer from milk to cheese.

• Milk casein is the principal yield determining factor. Casein contributes absorbed water and minerals as well as its own weight. Cheese quality limits the ratio of moisture/casein, a ratio which corresponding to MNFS.
• Fat is also a principal yield component. Fat interferes with syneresis and, therefore, also contributes more than its own weight, but if other conditions are adjusted to maintain constant MNFS, then fat contribution to yield is dependent only on the conversion factor of fat from milk to cheese (i.e., fraction of milk fat recovered in the cheese).
• Cheese moisture. A 1% increase in Cheddar cheese moisture causes about 1.8% increase in cheese yield, partly because more moisture means more whey solids and salt are recovered in the cheese (eg., given 90 kg cheese/1000 kg milk, a moisture adjustment to 36% would result in 91.6 kg cheese/1000 kg milk)
• Cheese salt. An extra 0.1% salt means an extra 0.14% yield of Cheddar cheese if the moisture content is increased accordingly.
• Milk quality factors: somatic cell counts, psychrotrophic bacteria, protein quality etc. See Raw milk quality.
• Increasing time and temperature of milk pasteurization increases cheese moisture retention and the recovery of whey proteins and soluble solids. There doesn't seem to be any consensus on how much is desirable but it's safe to say that it depends on the type of cheese and the quality standards of the manufacturer.
• Process control parameters (See Cheese making step by step)
  • Careless cutting.
  • Heating too fast at early stages of cooking
  • Salting too soon after milling of Cheddar allows rapid salt uptake which in turn causes rapid synerisis and increased solubility of casein. Yield is, therefore, reduced by losses of protein, fat and soluble solids.
  • High temperatures during pressing cause loss of fat.
  • Proteolytic cultures or coagulating enzymes cause protein losses before and after cutting.
  • Washing removes soluble solids.
  • Working as in Mozzarella removes fat and soluble solids. Loss of soluble solids is minimized by equilibration of the wash water with the cheese moisture.

With respect to yield the cheese maker's objectives are to:

1. Obtain highest MNFS (moisture in non-fat substance) consistent with good quality to maximize moisture and the recovery of whey solids.
2. Standardize milk to obtain maximum value for milk components consistent with good quality (eg., adjust P/F to maximize cost efficiency).
3. Minimize losses of fat and casein in the whey.

It is absolutely vital to be able to measure and maximize yield efficiency. This means maximizing the return (or minimizing the loss in the case of lactose) from all milk components entering the plant. This includes obtaining maximum returns for whey non-fat-solids, whey cream and cream skimmed during standardization. In general the highest return for all milk components, is obtained by keeping them in the cheese, but this may not always be the case.

Yield efficiency can be determined by monitoring recovery of milk components and losses in the whey as recommended by Gilles and Lawerence N.Z.J. Dairy Sci. Technol. 20(1985):205. By keeping accurate records of all incoming milk components and their distribution between cream, cheese, whey cream and defatted whey it is possible to determine the plant mass balance.

Purposes of Calculating Predicted Yields

1. Provide a target against which to judge actual yields and determine mass balance within the plant
2. Flag errors in measurement: eg. weights of milk or improper standardization etc.
3. Early signal of high or low moisture content which allows adjustment on the following vats. This can be met by rapid moisture tests (microwave) which is sufficiently accurate for this purpose 

The Van Slyke and Price Formula

The formula most often used for Cheddar cheese is the Van Slyke formula which was published in 1908 and has been used successfully ever since. The Van Slyke formula is based on the premise that yield is proportional to the recovery of total solids (fat, protein, other solids) and the moisture content of the cheese.

F = Fat content of milk (3.6 kg/100 kg)

C = Casein content of milk (2.5 kg/100 kg)

0.1 = Casein lost in whey due to hydrolysis of -casein and fines losses

1.09 = a factor which accounts for other solids included in the cheese; this represents calcium phosphate/citrate salts associated with the casein and whey solids

M = moisture fraction (0.37)

This formula has several important limitations:

• First, it's difficult to measure casein. Many plants use total protein in the predictive formula and multiple by a factor to estimate casein. The classical procedure for casein determination is Rowland Fractionation which is too involved for most cheese plants. I recommend that two or three silo samples be sent to a private lab every 4 weeks to monitor seasonal variation in the casein fraction of protein. Alternatively the casein content can be estimated from the equation given in Standardization of milk for cheese making.
• A second difficulty is that the formula fails to consider important variables such as variation in salt content and whey solids.
• Third difficulty is that the equation is quite specific to Cheddar.

Many other formulae have been developed and used. Probably the best proven formulae are those developed in Holland where commercial cheese manufacturers have been making good use of predictive yield equations for many years. Emmons et al. have developed a formula which has general application. See Emmons et al. Modern Dairy, Feb., 1991 and June, 1991; J.Dairy Sci. 73(1990):1365-1394. See also references listed in Dairy Science and Technology General References.

Standards: Moisture 55%; Fat 22%

Traditional Procedure (Structured Feta)

1. Standardize milk to P/F = 0.90 and pasteurize (72C, 16 S or 62C, 30 min.). The Greeks prefer a perfectly white smooth product made from sheep's milk. Goat's milk also produces a white cheese. If desired, a smoother cows' milk product can be made by selecting milk with higher fat contents in the range of 5.5 to 6.0%. The undesirable cream colour of cows' milk can be removed by treating the milk with 0.03 - 0.04% titanium dioxide. Titanium dioxide is diluted with 10x its weight of warm water and added to the milk before renneting. Whiter cheese can also be produced from cows' milk by homogenizing the milk.
2. Adjust temperature to 30C. Add 3% of S. lactis and/or S. cremoris starter. and 3 g lipase per 1,000 kg milk. Ripen for about an hour until TA increases by at least 0.05% and pH is 6.6 - 6.5.
3. Measure 120 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk. Agitate for 3 minutes and then allow milk to set. Setting time should be 45 - 60 min.
4. Cut the curd using Omega" (12.8 mm knives) knives.
5. Stir gently for 20 min.
6. Dip curd and whey into rectangular forms on a drain table.
7. Drain for two hours at 30C, then place the curd in a room at 18C and 85% RH. In the absence of such a room, cover the cheese with a clean cloth and store overnight at room temperature and humidity.
8. When the pH is 4.7, 20 - 24 hrs. after adding culture, take the cheese out of the hoops, weigh to the nearest 0.1 kg, and cut into 10 cm. cubes.
9. The required salt is 50 g of salt per kg of cheese. Weigh all the salt for all the cheese at once and distribute it uniformly by rubbing salt on all sides of the cheese surfaces. Place the cheese in 1 l plastic tubs with the lids partially open to allow some drying off of the cheese, and store at room temperature for 24 h. An alternative process, is to dry off for 1 day under a damp cloth and then store in barrels or canisters for up to 30 days at 8 to 10C. After this ripening period, the cheese may be consumed as is or stored in 8% brine.
10. Add sufficient 8% brine to cover the cheese, and ripen at 8-10C for up to 30 days. Subsequently store at 2-4C until consumed. The brine solution should contain 0.06% calcium chloride and sufficient acetic acid (vinegar) to adjust the pH to 4.6.

Distribution

Typically, Feta cheese is packaged and distributed to retailers and restaurants in one of four forms: (1) Cubes and brine in small tubs; (2) Crumbled product in a gas flushed package (nitrogen) ready for addition to salads; (3) Vacuum packed blocks; (4) Bulk shipments of cubes in large containers.

Process and Quality Control Notes

• At least 0.05 increase in TA before renneting
• pH 4.7 before surface salting
• Yeast and mould counts are the best indicators of hygienic problems. The low pH keeps bacterial spoilage to a minimum.
• A comfortable best before date is 6 months after manufacture. Good manufacturing practice and storage can achieve 12 months shelf life.

UF Procedure (Cast Feta)

1. Standardize milk to P/F = 0.80.
2. Ultrafilter until retentate is 40% solids.
3. Add 3% S. lactis culture and 250 ml rennet/1,000 kg of precheese.
4. Quickly pour into 1 l plastic containers (3/4 full). Cover and allow to ripen to pH 4.8 (18 - 24 hrs.).
5. Add salt (3% of weight of cheese) to surface.
6. Store at 18C for at least 1 week before consumption.

Standards: 56% moisture; 22% fat

Procedure:

1. Standardize milk to 0.86 P/F and pasteurize.
2. Add 3% S. lactis and/or S. cremoris starter and spores of P. camemberti or P. candidum. according to the manufacturer's directions. Alternatively, mould spores may be sprayed on to the salted cheese after draining. Ripen 1 hr. at 32oC or until TA increases by 0.05%.
3. Measure 250 ml rennet per 1,000 kg milk . Dilute rennet with 10 volumes of water before adding it to the milk. Agitate for 5 min. Setting will occur in about 15 min. but do not cut until 45 min. after renneting. The pH should be 6.2 - 6.3.
4. Cut curd using Omega" (12.8 mm knives) knives. Allow the curd to settle for 1 hr.
5. Drain the whey down to the level of the curd. Dip the curd and remaining whey into cylindrical Camembert moulds. The preferred mould dimensions are 11.5 cm in diameter and 11.5 cm high. Moulds available in the Food Science pilot plant are 8.5 cm in diameter and 10.5 cm high. Fill the moulds quickly to 1 - 2 cm from the top. Do not refill.
6. Turn the hoops 4 to 6 times within 4 to 5 h. hrs. and then occasionally until pH is 4.6-4.9 (8 - 12 h after adding culture).
7. Weigh sufficient salt to provide 8 g of salt per cheese. Dry salt the cheese (6 - 9 g salt/cheese) by rubbing the salt on all surfaces. Store the cheese at 85% RH and 12 - 14C for 24 h, or place the cheese on plastic mats in large plastic tubs with the lids partially open to allow some drying off of the cheese, and store at 12 - 13C for 24 h. 
8. If culture is to be sprayed on the cheese, disperse culture in water and spray on all surfaces of the cheese. Store the cheese at 95% RH and 12 - 14C for 6-12 days, with daily turning, until a luxurious growth of white mould is evident. Alternatively, the cheese can be ripened on plastic mats in large plastic tubs with the lids slightly open to some oxygen entry for mould growth.
9. Pack in waxed paper or foil and store at 4-8C. Camembert cheese is fully ripe when the entire cheese is soft and creamy. The pH will increase to near 7.0 or above, especially on the surface.

Process and Quality Control Notes

• Camembert has some special safety concerns because the acidity decreases (pH increases) dramatically due to the proteolytic action of enzymes produced by the white moulds. This is a particular concern with respect to aciduric pathogens such as E. coli 0157: H7 and Listeria monocytogenes which survive the initial acidic conditions and then grow when the pH increases during ripening. Raw milk Camembert is, therefore, of particular concern relative to hard ripened cheeses.
• To prevent accumulation of pathogens, Camembert curing rooms must be cleaned and sanitized regularly. It is no longer acceptable to cycle Camembert continuously through the same curing rooms.

Grading Schedule for Brie and Camembert (after Shaw, M.B., 1981, The manufacture of soft, surface mould ripened cheese in France with particular reference to Camembert. J. Society of Dairy Technol. 34(4):131).

1. Cheese shape and exterior appearance
   1. Regular shape, thin rind, white with some red streaking due to red organisms (4 to 5 points).
   2. Irregular shape, malformed sides, irregular rind thickness, irregular white mould growth with spots of other moulds, 'toad skin effect', (3-3.5 points).
   3. Irregular shape, slimy rind, very moist, numerous spots (less than 2.5 points).
2. Colour and consistency of body.
   1. Light creamy colour, very little or no openness in texture, supple body, smooth, not runny at consumption temperature (4 to 5 points).
   2. Some discolouration, some openness, slightly layered, body too firm or too runny, (3-3.5 points).
   3. Very discoloured, much openness, very firm or runny, granular, layered (less than 2.5 points.
3. Flavour and aroma
   1. Pleasant, characteristic, rather mild with good aroma (8 to 10 points).
   2. Neutral, slightly acid, very slightly bitter, slightly salty, slightly ammoniacal (6 - 7.5 points).
   3. Over acid, bitter, very salty, metallic, pungent, very ammoniacal, soapy taste (less than 5.5 points).

Introduction

The origin of mould ripened cheese is lost in antiquity. It was made in France at least as early as the Roman era. The name" Roquefort" first appeared in the year 1070. Roquefort cheese is made from ewes' milk, and the trade name is protected throughout the world. Other cheese varieties that are ripened by the mould Penicillium roqueforti include Blue (Bleu, Blue-veined), Gorgonzola (Italy), Stilton, Wensleydale and Dorset Blue (Blue Vinney) of England, Niva of Czechoslovakia, Danablu and Mycella of Denmark, Nuworld, U.S. and Errmite, Canada. P. roqueforti has been known by other names such as P. glaucum, P. gorgonzola and P. stilton. A white mutant of P. roqueforti was developed by Knight of Wisconsin and the resulting cheese is called Nuworld.

Standards: 47% moisture; 27% fat. In practice, the fat content is usually higher.

Procedure

1. Pasteurize milk. P/F ratio of about 0.87 is desirable. Milk may also be homogenized before pasteurization to promote lipolysis in the cheese. If the milk is not homogenized, add 30 g lipase per 1,000 kg of milk. If the milk is highly coloured, 0.03 - 0.04% titanium dioxide diluted with 10x its weight of warm water may be added to the milk before renneting, to prevent green cheese.
2. Add 3% mesophilic lactic starter and ripen for about an hour at 32C until TA increases by at least 0.05% and pH is 6.6 - 6.5
3. Measure 200 ml rennet per 1,000 kg milk (dilute rennet about 20 times with water and add to the milk). Setting will occur in 20 - 30 min. but do not cut until 1 hr. after renneting.
4. Cut curd with Omega" (12.8 mm knives). Allow curd to settle for 10 min. then agitate gently to prevent matting. When the acidity is 0.02% above cutting acid (about 80 min. after cutting) push curd away from the gate and allow it to settle for 10 min.
   [Feta cheese can be made from the same vat as Blue cheese, by dipping some of the curd and whey into rectangular forms when the acidity is about .01% above cutting acid (20-40 min after cutting), and then proceeding from Step 7 in the Feta procedure above. Similarly, Camembert cheese can be made by removing some curd and whey at 45 - 60 minutes after cutting
   and proceeding from Step 5 in the Camembert procedure above.]
5. Remove whey to the level of the curd. Break up curd and remove remaining whey. Ditch curd and turn over after 10 min. After an additional 10 min. break up the curd to prepare for salting.
6. Add salt, 1% of weight of curd. Sprinkle blue mould powder (Penicillium roqueforti over all the curd. It should look like well peppered scrambled eggs. Mix the mold powder thoroughly, and then place curd in cylindrical hoops on a drain table. Be certain that blue cheese is kept well apart from other cheeses in the make room.
7. Turn cheese 5 - 10 min. after filling and then at 30 min. intervals for 2 Omega hrs. Cover with broad cloth and incubate overnight at room temperature for 16 - 20 h or until cheese pH is 4.5 - 4.7.
8. Weigh sufficient salt to provide 50 g of salt per kg of cheese. Salt the cheese by rubbing the salt on all surfaces. Store the cheese at 85% RH and 12 - 14C for 24 h, or place the cheese on plastic mats in large plastic tubs with the lids partially open to allow some drying off of the cheese, and store at 12 - 13C for 24 h.
9. If desired, the cheese can be treated with paraffin (waxed) before skewering and ripening. Alternatively, the cheese may be turned and brushed regularly while curing (Step 11) to encourage development of smear on the surface.
10. Put about 60 holes on both sides of each cheese with a 3 mm diameter skewer.
11. Store the cheese at 95% RH and 12 - 14C for 6 - 8 weeks. Alternatively, the cheese can be placed on plastic mats in large plastic tubs with the lids slightly open to allow some oxygen entry for mould growth, and ripened at 12 - 14C. Turn every day for several days and then turn once a week. The pH should increase to 6.0 - 6.25 after 8 weeks.
12. Vacuum pack and store at 7C until consumed (up to 3 months).

Curing

Few lactic starter bacteria survive the first few weeks of curing due to acid and salt inhibition. P. roqueforti becomes evident 8 - 10 days after pricking. This mould grows well because it is more tolerant of salt and low oxygen than other moulds. The smear which forms on the surface is due to B. linens or B. erythrogenes. Too much smear is undesirable.

Activities of mould lipases and added lipases produce butyric, caproic, caprylic, capric and higher fatty acids. A predominant flavour compound is methyl-n-amyl Ketone (heptanone 2).

Caprylic acid CH3(CH2)6.COOH

Methyl-n-amyl Ketone CH3(CH2)4.COCH3

Introduction

The description "Brine" is used to distinguish brine salted Brick cheese from the modern version which is similar to Colby. Brine Brick is a sweet, mild version of German Brick.

The acidity of Brine Brick cheese is determined mainly by the amount of lactose removed during washing. There is little acid development until after hooping because the inoculum is small and the milk is not ripened before renneting. . It is mild and sweet in flavour and lacks the sharpness of Cheddar and the strong flavour of Limburger and German Brick.. Brine brick cheese should be clean, well shaped, free from checks and moulds and have a rind with a predominantly smooth surface. The cheese should present a neat attractive appearance and be of uniform size and shape. The sides should be square, not bulged.

Standards: 42% moisture; 29% fat.

Procedure

1. Pasteurize whole milk. Milk standardized to P/F = 1.04 will make a legal cheese but a higher fat cheese is preferred. P/F = .90 is suggested.

2. Add 0.25% of an active lactic starter at 30C. Normally Lactococcus. lactis and/or . cremoris is used but heterofermentative lactics such as Leuconostic mesenteroides subsp. cremoris and/orLactococcus. diaceteylactis may be used to promote an open structure.

3. Add a smear culture according to manufacturer's instructions. Alternatively, 'old to new' smear inoculation may be preferred.

4. Cheese colour may be added at the rate of 6 - 8 ml/1,000 kg milk when the cattle are off fresh pasture.

5. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk, immediately after adding the starter. Setting should be complete in 20 - 30 minutes.

6. Cut curd with 1/4" (6.4mm) knives when the curd breaks cleanly with a spatula. Acid development at this stage should be minimal (whey pH 6.5 - 6.6).

7. Agitate gently for 10 min. and then begin to cook. Follow the heating schedule carefully. Heating is required to firm the curd and obtain the correct moisture. 

8. Drain the whey to a level of 2.5 cm above the curd.

9. Add water at 36C. The required amount is 50% of the original weight of milk -- or about the equivalent of the amount of whey removed. Hold the curd in the water with gentle agitation for 15 min to allow the lactose in the curd and water to equilibrate. Short holding times result in acid cheese. Longer holding times (or excess water) results in bland cheese.

10. Drain the whey/water to a level 2.5 cm above the curd.

11. Dip the curd and whey into rectangular perforated forms on a drain table. The curd and whey may be moved with a positive rotary pump. Add curds to each form in rotation until they are full but not heaped up.

12. Turn the hoops at 5, 10, 30, 60, and 90 minutes. Add the metal followers after the first turn. If the curd does not form smooth sides, a little hot water may be sprayed over the curd to close up the cheese and form a good finish.

13. Place in 22 - 25% salt brine for 24 hrs. at 10 - 15C. Dry salt the exposed surface of the cheese. Brine pH should be about 5.3.

14. After removal from the brine, the cheese should be placed in a curing room at approximately 15C with a relative humidity of 90%. Alternatively, the cheese can be placed on plastic mats in large plastic tubs with the lids slightly open to allow some air exchange and maintain humidity. During curing, film yeasts, corynebacterium such as Bacterium linens and other organisms form an orange-red smear on the surface of the cheese. The growth is quite luxurious in 2 weeks. The smear grows only on the surface but the enzymes from the smear penetrate the cheese and break down the protein to produce the desired flavour.

15. Gently wash and turn the cheese every day for about 12-15 days. Washing is done with a damp cloth dipped in a 20% brine solution. Moisten the entire surface of the cheese with the salt water and remove any mould that appears.

16. After the smear has developed sufficiently (12 -15 days), rinse the cheese with cold water, gently brush off excess smear, and then allow the cheese to dry. If a milder flavoured cheese is desired, the smear may be washed off the cheese at an earlier date.

17. After the final washing, dry the cheese for 4 - 6 hrs. and then vacuum pack. Place the packaged cheese in a curing room at 5 - 7C for 1 - 3 months.

Process and Quality Control Notes

1. Acidity: Excessive acidity can result from too much culture. The pH at 3 - 4 days should be 5.1 - 5.2

2. Gas formation: Coliform bacteria may grow in the cheese during draining and salting causing early gas that gives rise to pinholes or to a spongy condition. Coliform organisms can be controlled by pasteurization and by avoiding post pasteurization contamination. Late gas formation by Clostridia organisms may occur due to insufficient acid and salt. The pH should be 5.1 - 5.3.

3. Lack of Smear Development: A smear will not grow if the humidity in the curing room is too low. If the curing room is 'too clean' it may be necessary to inoculate the surface of the cheese from a previously ripened cheese or inoculate the milk with commercial smear cultures.

4. Mould Growth: If the cheese is not washed often enough, moulds may grow on the cheese. The moulds will not grow if a good smear is developing. 

Colby cheese was named after a township in Southern Wisconsin in the 1880s. Colby is high moisture, open-textured, soft-bodied and quick-curing. It is sometimes called Farmer's cheese. The make procedure for Colby is the same as for Cheddar until the correct acidity is attained for dipping. At this time, the final acidity of Colby is adjusted by washing to remove lactose and acid, while in Cheddar manufacture lactose is removed by Cheddaring, a process of further fermentation and syneresis.

Standards: 42% moisture; 29% fat.

Procedure

1. Standardize milk to P/F 0.96, pasteurize and cool to 310C before adding starter.
2. Add 1.5% of S. lactis and/or S. cremoris starter. Ripen for 1 hr. or until acidity increases by 0.01%.
3. Measure 70 ml cheese colour per 1,000 kg milk. Dilute 20x with water and add to milk
4. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk
5. Cut using 3/8" (9.5mm) knives when curd is firm. Agitate gently.
6. Start cooking (15 min. after cutting). Increase temperature from 31 to 39C during 30 min. Heat slowly at first -- no more than 1C every 5 min.
7. Hold at 39C until whey pH is 6.2 - 6.3. This process should take 75 min from the time the temperature reaches 39C or 2 h from the time of cutting. If the acidity is increasing too quickly the temperature may be raised slightly (maximum 40C) to retard the culture.
8. When whey pH is 6.2 - 6.3 drain the whey down to the level of the curd.
9. Add water at 15C until the curd-water mixture is 26C. If the curd is to be washed in a curd table, transfer curd to the curd table leaving about 5 - 8 cm of whey in the bottom of the table. Add water (7 - 14% of original weight) at the required temperature to give a final temperature of 26C. This has advantages over washing in the vat: (1) Greater efficiency because a smaller capacity and less expensive curd sink is used for washing while the setting vat is used to begin another batch; (2) The amount of wash water which must removed from the whey or otherwise disposed is reduced.
10. Stir when adding water and for an additional 15 minutes. If wash water is below (15C) use less water. Colder water produces a higher moisture cheese. Warmer water produces a low moisture cheese.
11. Drain completely by piling curd at the sides of the vat. Curd should not mat.
12. Add salt at the rate of 2 Omega kg/1,000 kg of milk and stir well. Allow 15 min. for the salt to dissolve before hooping.
13. Hoop in 20 lb. (9 kg) Cheddar hoops. Cheese may lose shape in large sizes.
14. Press overnight at 75 kPa (10 - 20 lbs/in2). Start with low pressure and gradually increase to 75 kPa. In modern commercial practice, pressing is often shortened to as little as one hour.
15. Vacuum package in film and cure at 7 - 13C for 1 - 3 months.

Colby cheese has higher moisture and a softer body than Cheddar, and never attains the sharp character of Cheddar.

Defects

1. Acid-sour flavour: This defect may be caused by too much acid development in the vat before dipping. It may also be caused by poor culture activity and a lack of acid development at dipping. If the culture is not growing properly and acid is not being produced, then the curd will be high in moisture and lactose. The lactose later ferments to give a sour acid cheese.
2. Fermented flavour: This is caused by a lack of acid development due to a poor starter or starter inhibition. If the cheese pH is above 5.4, the cheese will inevitably be fermented and fruity.
3. Woody, corky body: This defect may be caused by lack of acid development, washing the curd with too much water, prolonged holding of the curd in the water, or by cooking over 40C.
4. Mottled cheese: This defect is usually due to lack of acid development, or by salting too soon after dipping. Short draining time before salting and pressing may also result in slight mottling.

Yield of Cheese

The yield of Colby cheese should be from 10 to 11 kg of cheese per 100 kg of 3.5% milk with 40 - 42% moisture.

Gouda cheese originated in the Netherlands and is similar to Edam. Normally Gouda has a higher fat content than Edam but fat in dry matter does vary from 30 - 50%. In Canada, Gouda cheese must contain a minimum of 28% fat (49% fat on dry matter basis) and a maximum of 43% moisture. Gouda is made in round or block forms and the cheese vary in weight from 600 g to 20 kg. A gas-forming culture is used to induce eye formation.

Procedure

1. Standardize milk to protein/fat ratio of 1.07 and pasteurize.

2. 1 - 2 ml of annatto per 1000 kg of milk may be added during the winter months.

3. Add 0.75% starter culture. Mixtures of Streptococcus lactis and Leuconostic cremoris and Streptococcus diacetylactis are recommended. Ripen until an increase of 0.005 - 0.01 in titratable acidity is achieved.

4. Measure 190 ml rennet/1000 kg of milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk.

5. When curd cuts cleanly, cut curd into 0.5 - 1.0 cm cubes taking 10 - 15 minutes. Stir curd to float in whey for an additional 20 - 30 minutes. Whey pH should be 6.4 - 6.45.

6. Run off one-third of whey and slowly add water at 60C to give final temperature of 36 - 38C. The volume of water should be 20 - 25% of the amount of milk. Add the water slowly during 15 - 20 min with continual stirring. Continue stirring for another 15 min. after all the water is added.

7. Allow curd to settle, and press under the whey by covering the curd with steel plates for at least 10 min. In commercial practice this is accomplished by moving the curd and some of the whey onto a press table.

8. When curd is consolidated under the plates, drain the whey and cut to fit cloth-lined hoops. Press at 14 psi for 5 - 8 hrs. with occasional turning. After first turning increase pressure from 14 - 28 psi. The pH after pressing should be 5.3 - 5.5.

9. Immerse in 20% salt brine for periods as indicated below. The pH should be 5.15 -5.25.

10. Pack in plastic film and incubate at 15C, 4 - 6 weeks. Then store at 100C for 6 - 12 months.

The pH of Gouda cheese increases during ripening. At 8 weeks the pH should be 5.3 - 5.5.

Montasio is a washed curd variety of Italian origin. Relative to other Italian varieties such as Romano and Parmesan, Montasio employs a low cooking temperature (final temperature 43C) but still requires a thermophilic culture. The curd may be pre-pressed under the whey to obtain smoother and more uniform texture. Lipase may be added to produce a more piquant flavour. Montasio is produced in wheels of 2 - 8 kg and is ripened 2 - 4 months for mild table cheese and 12 - 18 months for grating cheese. The mild version is normally vacuum packed before curing. The aged version is cured at 10C and is washed and turned regularly. After several weeks, the ripening cheese may be oiled, waxed or vacuum packed. Montasio is similar to Friulano which was developed in Canada. 

Standards: 40% moisture; 28% fat.

Procedure

1. Standardize milk to P/F = 1.07 and pasteurize.
2. Add 1.0% thermophilic starter (0.5% each of S. thermophilus and L. bulgaricus) at 310C. Ripen for 1 hr. or until acidity increases 0.01%.
3. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk. Curd should be firm enough to cut in 25 - 30 min.
4. Cut into cubes with 1/4" (6.4 mm) knives when curd is firm.
5. Turn on steam. Heat (slowly at first -- 2 degrees every 5 minutes) to a final temperature of 39C. Hold at 39C until the pH of the whey is 6.1 (about 2 hr. from the time of cutting).
6. Drain whey to the level of the curd.
7. Add hot water (60C) until the curd-whey mixture is 43C. Hold at 43C for 10 min. with agitation.
8. Drain completely.
9. Place curd in cylindrical forms and let drain at room temperature overnight.
10. Place in salt brine for 12 hrs.
11. Vacuum pack and cure at 10 - 12C for 1 - 3 months.

The manufacturing procedures for Pasta Filata types (Mozzarella and Pizza cheese) and Provolone are similar. These cheese are made using the principle of working or kneading the curd to produce the desired melting and stretching properties. The principal differences are: (1) Pasta Filata types contain less fat than Provolone; (2) In addition to mesophilic cultures, Provolone requires thermophilic starters to promote curing while the Pasta Filata types are usually made with mesophilic starters which are destroyed or severely retarded during the process of working. (3) Provolone is suspended with ropes at 85% humidity for curing. The following procedure is for Provolone.

Standards: 45% moisture; 24% fat.

Procedure

1. Standardize milk to P/F = 1.17 and pasteurize.
2. Add 1 to 2% mesophilic starter and thermophilic starter (S. thermophilus and L. bulgaricus) Ripen at 300C for 1 hr. or until acidity increases 0.01%.
3. Add lipase enzymes as directed by manufacturer's instructions.
4. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk. Milk should set in 30 min.
5. Cut when curd is firm with 1/4" (6.4 mm) knives.
6. Agitate gently for 10 min. and then cook according to the Cheddar heating schedule to a final temperature of 39C in 30 min.
7. Stir the curd and whey for about 10 min., then allow the curd to settle for 5 min. Drain 1/3 of the whey and store it in a cylindrical vat for use in Ricotta cheese manufacture. Resume agitation until the pH of the whey is 6.1 - 6.2. Then allow the curd to settle for 5 min. before removing the remaining whey.
8. Form the curd into a continuous slab 12 - 20 cm (5 - 8") deep and 45 cm (18") wide along the sides of the vat. Trim the edges and put loose curd under the slab.
9. After 10 min. cut the slab into blocks 20 - 30 cm (8 - 12") wide and turn every 15 min. until the pH is 5.4. Pile the blocks two high on the third turn.
10. When cheese pH is 5.4 and curd strings in 77C water, mill or cut the curd into strips as in Cheddar cheese manufacture. If stretching is to done by hand, wait until the pH is 5.2 - 5.0. Test the curd by dipping a small piece in hot water for 30-45 s or until the whole piece is heated to 55-60C. Remove the curd from the water and stretch. When the curd is ready to work, it should stretch easily to 25 - 50 cm without breaking. Do not hurry to start working.
11. Work the curd in a mechanical stretch machine. Or, if working and stretching is to be done by hand, cover the curd with its weight of hot (>70C) water. Fuse, stretch and work curd until it looks and stretches like taffy. The internal temperature (greater than 50C) and pH (5.3 - 5.0) must be right for this appearance. Work and roll the stretched curd into desired shapes. Beginners will not want to make the large styles at the first attempt. Learn to seal the ends of the curd first. Keep curd hot while working by dipping it in the hot water. When the curd is formed and sealed, drop it in cold water until chilled and hardened in shape. If the curd gets to hot (>60C) or remains in the hot water too long, it will lose stretchability and mouldability.
12. Float the curd in 22% salt brine. Salting time depends on the size of the cheese. Most of the cheeses made in our teaching labs at Guelph are less than 1 kg. Three to four hours of brining is sufficient for these small cheeses.
13. Hang the cheese in the conventional smooth rope or plastic netting. The cheese may be lightly smoked in a cool room for 2 - 4 hrs. Alternatively, vacuum pack the cheese.

Process and Qaulity Control Notes

• The pH at the time of draining is critical to the retention of calcium in the curd, and Ca is a principal determinant of curd strength. For a stronger curd drain the whey at higher pH to retain more Ca.
• Other pasta filata cheese such as Mozzarella and Pizza are close cousins of Provolone. Pasta filata cheese intended for use on pizza or similar application should be aged for 10-12 days to improve melting properties. This effect is possibly due to proteolysis or perhaps due to equilibration reactions among casein and the Ca salts of phosphate and citrate.

Standards: 39% moisture, 30% fat.

Procedure

1. Standardize milk to P/F = 0.91, pasteurize and cool to 31C before adding starter. Note a P/F ratio of .94 - .96 will produce a legal cheese with respect to fat content (31% fat wet basis, or 50% fat dry basis). However, a somewhat lower P/F ratio incorporates more fat in the cheese which is economically desirable when the price of milk protein exceeds the price of milk fat.
2. Add 1% of S. lactis and/or S. cremoris starter. Ripen until acidity increases by 0.01% or until pH decreases by 0.05 units (about 1 h.).
3. Measure 70 ml cheese colour per 1,000 kg milk (optional). Dilute the colour with 10 volumes of water and add the mixture to the milk
4. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk.
5. Cut, using 3/8 inch (95 mm) knives when curd is firm. Agitate gently.
6. Start cooking 15 min after cutting. Increase temperature from 30C to 390C during 30 minutes. Heat slowly at first - no more than 1C every 5 min.
7. Hold at 39C until pH is 6.1 (about 75 min from the time the temperature reaches 39C or 2 h from the time of cutting). If the acidity is increasing too quickly, the temperature may be raised slightly (maximum 40C) to retard the culture.
8. When curd pH is 6.0-6.1 (whey pH 6.2-6.3) remove the whey. After the bulk of the whey is removed stir out the curd two or three times to facilitate maximum whey drainage.
9. Pile the curd 13-15 cm deep along the sides of the vat and allow to mat. After about 10 min, trim the front edge and cut the curd into blocks about 25 cm wide. Turn the blocks every 15 min until the pH is 5.4-5.3 (about 2 h after dipping). At the second turn, pile the blocks two high and then three high at the third turn.
10. Cut the blocks of curd into 10-13 cm (4-5 inch) strips and pass the strips through the curd mill. Stir the cheese curds every ten min or so until the cut edges become round and smooth (about 30 min after milling).
11. Distribute the salt uniformly over the curd and mix well. The final salt content of the cheese should be about 1.7%. Calculate the required amount of salt as follows:\
    1. Estimate cheese yield as: Yield = (% fat + % protein) k where k is a factor dependent on cheese moisture. K values corresponding to 35, 36, 37, 38 and 39% moisture are 1.40, 1.42, 1.44, 1.46 and 1.48, respectively.
    2. The required amount of salt is 2.5% of the estimated yield. This value is higher than the final 1.7% content because considerable whey drainage occurs after salting.
12. After the salt is well absorbed and the flow of whey has stopped, the curd is ready for hooping. Use 20 lb (9 kg) hoops and place 22 lb of curd in each hoop. The hoops should be lined with plastic, single service press cloths.
13. Press overnight at 75 kPa (10 - 20 lbs/in2). Start with low pressure and gradually increase to 75 kPa. Vacuum treatment to remove air from the cheese and increase the rate of cooling may be applied during or after pressing. In modern commercial practice, pressing is often shortened to as little as one hour.
14. Vacuum pack the cheese blocks and store at 0-16C for curing. Cold curing (5-8C) produces the best cheese but ripening is slow. Warm cured cheese (10-16C) develops flavour rapidly but quality control is more difficult. Raw milk cheese by law must be "held at 2C or more for a period of 60 days or more from the date of the beginning of the manufacturing process". (Canadian Food and Drug Act and Regulations Sections B.08.030 and B.08.042 to B.08.048).

Grading

Special samples for grading should be kept at 14.4-15.5C for 21 days after the date of manufacture. These samples cured at high temperature give an indication of the probable quality of the aged cheese. If, in the judgement of the grader, the cheese is not sufficiently mature to properly assess its quality, the grading should be deferred until it has reached a suitable maturity. Other samples should be taken from the curing room at about 3 and 6 months during a 9 month curing period.

Standards: 34% moisture, 25% fat.

Procedure

1. Standardize milk to P/F = 1.50 and pasteurize.
2. Add 1.5% thermophilic starters: 0.74% L. bulgaricus and 0.75% S. thermophilus. Ripen briefly (15 min.) at 32C.
3. Add lipase according to the manufacturer's instructions. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk.
4. Cut when curd is still somewhat soft using a double cut with 1/4" (6.4 mm) knives. Continue cutting until the curd is the size of rice grains.
5. Cook from 32 - 46C in 50 min.
6. When the pH is 6.1 - 6.2, allow the curd to settle. Then push the curd away from the gate and level it beneath the surface of the whey. Drain the whey. Cut portions of the curd to fit dressed hoops. In the Food Science lab, use a 25 kg cylindrical hoop.
7. Allow 20 min. without pressing, then stack the hoops double for 20 min. Reverse the hoops and hold for another 20 min. Then press for 60 min. Hold overnight at room temperature without pressure.
8. Place cheese in a salt brine for 48 - 96 hrs. (48 hrs. for 9 kg blocks).
9. Dry cheese for 48 hrs. at 10C.
10. Cure at 10 - 15C for at least 5 months and regularly rub the surface with mineral oil. Alternatively, the cheese may be vacuum packed.

Cheese composition should be 32% moisture, 21% fat and 5.5% salt.

Swiss (Emmentaler) cheese was first made in the fifteenth century in the Emmental Valley. Swiss type cheese made in other areas are known by local names: Gruyere (Switzerland), Allfauer Rundkase (Bavaria), Battlematt (Switzerland), Fontina (Italy), Traanon (Switzerland) and Samso (Denmark). Swiss is traditionally made in large 50 kg wheels.

The distinctive feature of Swiss cheese is the formation of eyes by the gas forming bacteria Propioni bacterium shermanii. The manufacturing procedure is designed to provide the right chemical composition for the growth of P. shermanii and the right texture (sufficient elasticity) for bubble formation. Important manufacturing parameters are: (1) high dipping pH (about 6.3) which promotes retention of minerals; (2) high cooking temperature (52C) which promotes mineral retention and the loss of both moisture and lactose by syneresis; (3) high final pH (5.3 - 5.4) and mineral content which promote elasticity. The final pH is influenced by the amount of Lactobacillus helveticus which is added in the starter because this organism is able to metabolize both glucose and galactose.

Standards: 40% moisture, 27% fat.

Procedure

1. Standardize milk to P/F = 1.1 by removing cream or adding skim milk. Do not add skim milk powder. Pasteurize.
2. Add starters through a fine mesh screen, especially if the starter was made with reconstituted skim milk. Use 0.1% S. thermophilus, 0.1% L. helveticus and 0.005% Propioni bacterium shermanii. Ripen briefly (10 - 15 min.) at 37C.
3. Measure 190 ml rennet per 1,000 kg milk. Dilute the rennet with 10 volumes of water and add the mixture to the milk.
4. Cut when curd is firm using 1/4" (6.4 mm) knives. Continue cutting until curd size is reduced to the size of rice grains. If curd is forming clumps, cut more vigorously and begin agitation as soon as rice grain particles are achieved. Cutting speed is increased as the curd becomes less fragile. Too much cutting initially will cause dusting. The cutting process should take about 5 min. Do not allow the curd to clump.
5. Stir out the curd with vigorous agitation until the curd is firm and resilient when gently pressed (30 - 60 min.). There should be little acid development at this point (pH 6.55 - 6.50).
6. Cook the curd from 37C to 52C in 30 min. Heat slowly at first ( 1 - 1.5C in 5 min.). Rapid heating causes "case hardening" with traps moisture and acid inside the curd particles. Curd cooked too slowly may also be too acid. Continue vigorous agitation to prevent matting until the pH is 6.3 - 6.4. Experienced cheese makers look for the proper `grip' before removing the whey. Curd pH should not be less than 6.3 at whey separation.
7. Stop agitation, allow the curd to settle and pump the whey into the moulding vat until the discharge pipe is beneath the surface of the whey. During this time check pump and pipes for air leaks. Shut off the pump and resume vigorous agitation to break up clumps. Then, pump the curd and whey into the moulding vat. Be careful to match output with input so that the curd is always covered in whey. When the make vat is nearly empty, recycle whey back into it to transfer all curd without drawing air. Make sure that the curd fills the vat evenly and forms a level surface under the whey.
8. Cover the surface of the cheese with a double layer of cloth and place the press plates on top. At this stage loose curd must not be added to the curd mass. Add weights and let stand for 15 - 30 min. and then drain the whey from the moulding vat. Let stand for 1 hr. Remove the press plates and the surface cloth and also remove all loose curd particles and protruding edges. Then replace the cloths, cover with terry cloth to help dry the surface, position the press plates and add the weights. Press for 12 - 18 hrs. at room temperature (at least 22 C).
9. Remove the press plates and cloths, and cut the cheese into blocks. Cheese pH at this time should be 5.2 - 5.4.
10. Place the curd in the brine (at least 23%) and liberally salt the surface. Brining requires 48 hrs. with frequent agitation.
11. After brining, immerse the cheese in the brine to remove salt particles from the surface and then store at 10C to dry the surface. Vacuum the blocks in pouches sufficiently large to permit expansion (15 - 20%) during eye formation.
12. Store at 10C for 8 - 10 days for cooling and pre-ripening. Then, transfer to the warm room (23C) for curing and eye formation.
13. When eye development is complete (2 - 3 weeks), place the cheese in the finishing cooler (2 - 5C) to stop eye development and to firm the cheese in preparation for cutting. Flavour development continues in the finishing cooler.

Acid development and ripening

Drainage in the press is affected by the rate of acid development which in turn is affected by the curd temperature and the activity of the organism. At dipping, the temperature is too high for any of the organisms to grow but as soon as the curd cools 49C, S. thermophilus begins to grow. The rods (L. helveticus) begin to grow about 5 h after dipping when the temperature in the cheese is about 45C and growth factors have been provided by the metabolism of the cocci. The following morning the temperature of the curd should be about 36C. Too rapid cooling does not allow enough acid development. The pH changes during curing are:

The numbers of both rods and cocci decrease rapidly during the first 15 - 30 days of curing. Propioni bacteria multiply rapidly to about 100 million/g during 6 - 8 weeks. Propioni bacteria ferment lactic acid and produce propionic acid, acetic acid, water and carbon dioxide. Eyes formed by carbon dioxide production should be 1.9 - 2.5 cm in diameter and should be spaced 2.5 - 7.6 cm apart. The number of eyes depends on the rate of gas production. If gas is produced too rapidly the cheese will be overset with many small eyes. Little or no gas production causes a `blind' cheese. Any factor causing weakness or brittleness of the curd will result in defective eyes.

Defects

1. Glasler: brittle curd resulting in defective or too few eyes.
2. Pressler: pin holes due to contamination with Aerobacter aerogenes or Bacillus polymyxa.
3. Nissler: Clusters or nests of holes due to lactose fermenting clostridia or an accumulation of fat in the area.
4. Late gas formation: due to Clostridium butyricum or Clostridium lentoputrescens. These organisms, especially the latter, produce stinker cheese, and are inhibited at pH<5.3.

Yield: 7.5 - 9 kg per 100 kg of standardized milk.

Ricotta cheese is made from heat-acid precipitation of proteins from whey or whey-milk blends. The best Ricotta is made from very sweet whey (pH 6.4 - 6.5) without any addition of milk or acid. During heating whey proteins begin to coagulate at about 70C. The rate of coagulation increases as the temperature is raised to 90C and a thick layer of curd forms on the surface of the whey. When coagulation is complete and the curd is firm (after 10 - 20 min. at 90C), the curd is removed with perforated scoops and placed in forms. After removing the first rise, addition of acid (to about pH 5.9) will induce a second rise of coarser curd. If the pH is correct the whey should become clear.

It is now uncommon to make Ricotta cheese from whey only because: (1) Sweet whey with pH>6.4 is not always available; (2) the traditional hand skimming process of removing the floating curd is hot and tedious; and (3) yields are low. All of these problems are avoided or reduced by adding milk or skim milk before heating. Whey pH as low as 6.1 is then acceptable, the curd can be recovered by mechanical means and the yield is increased. The following is a procedure for the manufacture of Ricotta cheese from blends of milk and whey.

Thanks to John van Esch for some fine tuning of the following procedure:

Procedure

1. Collect whey (pH>6.1) and weight it into a cylindrical vat. Sweeter whey (pH>6.4) is preferred. Immediately heat the whey to 50C to stop culture growth.
2. Add milk or skim milk (up to 25% of the total weight).
3. Heat by direct steam injection from the bottom of the vat to 80-85C without agitation.
4. Add citric acid (5% solution) to induce maximum coagulation of caseins and whey proteins. The required amount is about 140 g citric acid monohydrate per 1,000 kg of whey-milk blend. The required amount can be determined exactly by titrating a sample of the blend to pH 5.9-6.0 at 20C. Alternatively, add the acid slowly until the whey becomes clear.
5. Continue heating WITHOUT agitation to 90-95C.
6. Hold the curd for an additional 15 min. at >90C. Then scoop the curd into the forms using perforated ladles. Fill the forms in rotation until they are level full.
7. Cover the forms with a clean cloth, place chopped ice on the cloth, and roll the drain table into a cold room (0 - 4C). When the curd is cool it can be packaged in plastic tubs or wrapped in wax paper for immediate sale.

Notes: Ricotta cheese may also be creamed and/or pressed before packaging. A cured, dry Ricotta type cheese called Myzithra is made in Greece.

Introduction

Queso Blanco is a white, semi-soft cheese with a bland, slightly acid flavour and good slice ability. The cheese can be produced from whole milk or recombined milk by direct acidification at elevated temperatures. Milk is heated to 85C and held for 5 min followed by the addition of a citric acid solution. The curd is formed as a result of co-precipitation of casein and the whey proteins. Rennet curd is made from milk which has not been heated in excess of pasteurization temperatures (72C/16 s) and contains only the casein fraction of milk protein. Whey proteins constitute approximately 20% of the total milk protein, and their co-precipitation with casein leads to substantially higher yields in Queso Blanco compared to Cheddar and other rennet coagulated cheese.

Milk for Queso Blanco manufacture is standardized to a protein to fat ratio of 1.2. This will increase the total solids (TS) of milk from about 12% to 14-15% TS and produce yields of 16-18% (16-18 kg cheese per 100 kg milk).

After draining, the curd is salted hot and agitated manually or with forking agitators, hooped, and pressed. Chilling the curd overnight allows easier handling before packaging. Vacuum packaging is necessary to prevent mould growth. The cheese is held in refrigerated storage for about 2-3 days to allow the curd to become firm and sliceable.

Since Queso Blanco contains no added bacterial culture, it is important to avoid contamination of the curd. Contamination will result in sour, unclean flavours upon storage.

An alternate packaging system which minimizes contamination is to extrude the hot salted curd into sausage casings.

Queso Blanco normally contains 52-53% moisture, 22-24% protein, 16-18% fat, 2-3% lactose, 2.5% salt, and has a pH of 5.3-5.5.

Materials 

• Raw milk or recombined milk
• Citric acid monohydrate C4H8O5.H2O
• Calcium chloride dihydrate CaC2.2H20
• Skim milk powder
• Salt

Procedure

1. Standardize milk to a P/F of 1.2 using skim milk powder.
2. Weight out the required citric acid monohydrate. Dilute the required amount of citric acid monohydrate to form a 1.5% solution. The required amount of citric acid as a percentage of milk weight is calculated as:
   % citric acid monohydrate = 0.09124 + 0.07075 (% milk protein)
3. Heat standardized milk to 85C and hold for 5 min.
4. Slowly pump coagulant solution into the vat and agitate slowly. Turn on steam to maintain high temperature. Hold for 10-15 min to allow curd to settle.
5. Open gate and drain whey.
6. Trench and stir curd to allow maximum drainage.
7. Salt curd directly in the vat and mix thoroughly for uniform distribution. 
   Weight of salt = 2.0% of expected yield
   Expected % yield = 4.83 (% milk protein) -3.64 
8. Hoop while still hot.
9. Press for 3-4 hours at 75 kPa (11 lbs/in2)
10. Chill hoops overnight.
11. Vacuum package.

PANEER has been made in India for generations, mainly in the home. Milk is coagulated by lime juice, citric acid solution, sour whey, or lactic cultures. Citric acid solution generally gives a cleaner flavour to the Paneer than sour whey which may give off flavours and odours. Lime juice as a coagulant imparts a good flavour to the Paneer. Paneer made from 6% fat buffalo milk (in India) is supposed to be of the best body, flavour and texture. Paneer can also be made from cow's milk. Paneer pH is typically 5.7-6.0 and its composition when made from 6% fat milk is 54/7% moisture and 26% fat.

Procedure

1. Take cow's milk in a pre-sterilised stainless steel vessel and heat it to82C and hold for 5 min. After holding, cool slightly to 70C.
2. Prepare coagulant of 2% citric acid solution (generally, 2 - 2.5g citric acid is required to coagulate one kg of milk). Heat the coagulant to 70C so the temperature of the milk and the coagulant is the same. The quantity of coagulant added should be sufficient to give a clear whey separation wherein the colour of the whey tends to be a greenish white tinge. When adding the coagulant to the milk (at 70C), there should be very slow stirring so as not to break up the curd mass.
3. After the greenish white tinge of the whey is seen (pH: 5.7 - 6.0), a final slow stir is given and the curd allowed to settle for about 5 - 10 minutes. Then the whey is drained out through a muslin cloth and the coagulated curd collected within the cloth. During this period, the whey temperature should not fall below 63C.
4. Fill cloth lined hoops and press for 15- 20 min. Pressing can be done by a manual press.
5. Remove pressed Paneer from the hoop, cut into required sizes and immerse in chilled water (4- 6C) or 5% brine solution (4- 6%) for 2 - 3 hours to make it firm. After chilling treatment, the Paneer is surface-dried to remove extra free water and then vacuum-packaged in HDPE (high density polyethylene) bags.
6. Store at 5 - 8C (refrigeration temperature).

Notes:

Since moisture is high, Paneer is prepared and consumed immediately due to shelf-life problems. It can be cut conveniently into cubes, fried in oil and added in vegetable salads or garnished in curry preparations. Some people apply corn flour paste and barbecue it.

Manufacturing procedures may differ considerably and still yield a high-quality product. They differ chiefly in temperature of setting and in amounts of starter and rennet. Procedures differ also in the size of curd, creaming rates, type of cream, the degree of "cottage cheese flavour" and added condiments. With any procedure, though, it is vital that the cheese maker follow it carefully and consistently from day to day.

The short-set procedure is widely used chiefly because it can be carried out within one working day and the time in a vat is minimal. It can be considered as labour-saving because the approximate time for cutting may be predicted fairly closely and the cheese maker does not have to wait for the proper cutting time. Steps in this process are:

1. Add 5% of starter to pasteurized skim milk at 32C. Stir well for 10-15 min.
2. Add rennet at the rate of 3 ml per 1,000 kg of skim milk at the time the starter is added, or 1 to 1 Omega hours later. If the A-C test is used to determine the cutting time, take the A-C test sample before adding the rennet.
3. Determine the cutting time using pH measurements of the curd, the A-C test or titratable acidity of the whey. Optimum values for pH at cutting depend on the heat treatment and composition (total solids) of the skim milk. Generally, pH of 4.80 in the curd can be used for normal skim milk when rennet is used. Use 1.2 cm (3/8") knives.
4. After cutting, the curd is left undisturbed for 15 to 20 min while the water in the jacket is heated in preparation for cooking.
5. Raise the temperature of the heating water at a rate such that the temperature in the vat rises 0.5C each 5 min for the first 30 min. After this , the rate may be doubled and eventually tripled until a final cooking temperature of 54 - 57C is reached about 2 hours later. Stirring should be gentle to prevent shattering, yet frequent enough to prevent matting. If both matting and shattering occur, the rate of heating is probably too fast.
6. The proper firmness should be reached after holding 15 to 20 minutes at 54-57C. The curd should be checked frequently during cooking to ensure that it does not become too firm. The pH or acidity at cutting is the chief factor influencing the firmness of curd at the final cooking temperature. If curd is consistently too firm at 54-57C, the cutting acidity should be raised, or the cutting pH should be lowered slightly. If curd is consistently too soft at 54-57C, the cutting acidity should be lowered, or the cutting pH should be raised slightly. Judge firmness of curd after cooling in water to 15-20C.
7. After cooking, drain the whey until the whey first disappears below the surface of the curd mass, and then add the first wash water. If three wash waters are used, the first is at 20-25C the second at 10C and the third at 1.5-5C. If two wash waters are used, the first is at 15C and the second at 1.5-5C. The curd should remain in contact with each wash for 15 to 20 min and should be stirred frequently but carefully.
8. Trench the curd carefully while draining the final wash water. Continue draining until the free water has completely drained (30-60 min).
9. Add salt (1% of the weight of curd) either directly to the curd or in the cream.
10. Add homogenized cream (18%) to give 4% fat in the creamed curd. If cream of lower fat content is used it is necessary to increase its viscosity using stabilizers to prevent excess free cream in the curd.

Expected yield: 6 x casein content or about 14 - 16%.

The A-C Test

1. Add starter to the skim milk in the vat. Mix well.
2. Place a sample of the well-mixed starter and skim milk in the A-C test beaker. Cover and take precautions against cooling.
3. Add rennet to the skim milk in the vat immediately after taking the A-C test sample. Mix well.
4. Immediately suspend the A-C test beaker in the vat so that the surface of the skim milk in the beaker is a little below that in the vat. Cover the vat.
5. Periodically check the vat for coagulation. After it is coagulated begin to check the A-C beaker for coagulation with a spatula or thin knife with as little disturbance of the skim milk as possible.
6. As soon as coagulation in the A-C beaker is first detected, cut the coagulating skim milk 2 or 3 times with the spatula and repeat the operation at 5 min intervals.
7. Observe the surface of the A-C test samples for the appearance of fine lines of whey in the cuts made previously with a spatula. The A-C end-point is that time when the fine lines of whey first appear and usually occurs 1 - 20 min after coagulation is first detected.

Reference

Emmons, D.B. and Tuckey, S.L. 1967. Pfizer cheese Monographs -7. Cottage cheese and other cultured products. Pfizer & Co. New York, N.Y.

Quark (sometimes called European style cottage cheese or quarg) represents a group of soft fresh cheese of varying moisture and fat contents. The procedure described below produces a relatively firm, granular curd structure. If a smooth textured product (such as Baker's cheese) is desired, the pH at the time of breaking the curd should be 4.5 to 4.4 and no cooking is required. The soft smooth curd must then be separated in cloth bags or by a centrifuge. In Europe the majority of Quark and Cream type cheese are produced using ultra filtration to concentrate skim milk protein either before or after ripening.

Procedure

1. Pasteurize the skim milk at 62C for 30 min.
2. Cool the skim milk to 32C.
3. Add a low temperature cheese starter (Streptococcus lactis or cremoris) at the rate of 5%. Let milk set for 4-6 h until a soft gel is formed. The pH should be about 4.8 and clear whey should appear when the curd is cut with a spatula. Alternatively 1% of culture may be used with a setting time of 12-18 hours.
4. Stir gently to break up the curd and heat slowly to 52C. Initial heating rate should not exceed 0.5C in 5 min. Hold at 52C until the curd is firm (about 1.5 h from the time of breaking the curd).
5. Drain most of the whey and replace it with 10C water to leach the acid flavour from the curd. Washing may be omitted if you prefer an acid cheese. It may be convenient to drain the curd in a cloth bag, in which case, it could be washed by soaking the whole bag in cold water for 15 min.
6. Add cream or cream dressing to the curd according to taste. Suggestion: 4 - 8% using 18% homogenized cream.

Cream cheese according to the Food and Drug Directorate is the cheese made from cream or milk to which cream has been added. It may contain not more than 0.5% stabilizer and shall not contain more than 55% moisture and not less than 30% milk fat.

The following procedure is a cold pack method. For greater shelf life and smoother texture, cream cheese or Neufchatel cheese can be blended with 50% cream, heating, homogenizing and hot-packing. Neufchatel cheese is similar to cream cheese, but has a lower fat content. Cream cheese is now frequently made by ultra filtration procedures.

Conventional Procedure 

1. Standardize: Cream should be 11-20% fat. Cream of 11% fat is required to make a legal cheese.
2. Pasteurize the cream (70C, 30 min).
3. Homogenize at 1000-1500 psi (6900 - 10300 kPa) at 63C and cool to 30C.
4. Add 30 kg (lb) starter and 1 cc rennet per 1000 kg (lb) of cream.
5. When the acidity increases to 0.6 -.75 (pH 4.6) stir the curd thoroughly to remove lumps. Add water at 76C directly to the curd until the temperature is 51C. Curd should be smooth and creamy. Coarseness or mealiness is due to low fat or lack of acid development.
6. Pour the hot curd and whey into draining bags. Sterilize the bags in boiling water before use.
7. Allow the whey to drain freely for about 2 h. After the correct consistency is obtained, salt the curd with 0.75% salt.
8. Pack the cheese in appropriate sized moulds lined with Saran, press lightly and chill to 2C. 

Yield: 2.7-3.1 kg of cheese per kg of fat.

Flavouring: Many flavouring materials may be used such as olives, nuts, mayonnaise, pickles, relish and pimento.

Ultra filtration Procedure For Cream Cheese

The following procedure was developed by Maubois of France and is described along with other UF cheese making procedures by Glover (1985).

1. Pasteurize 11% cream.
2. Add 1% lactic starter.
3. Ultrafilter 3.3x based on fat content. This provides 30 kg of pre-cheese per 100 kg 11% cream. The pre-cheese will contain 36.5% fat (11 x 3.3), about 11% protein and about 48% total solids.
4. Ripen to pH 5.6.
5. Add .16 kg salt per 100 kg original cream.
6. Add .16 kg locust bean gum per 100 kg original cream.
7. Heat to 54C.
8. Homogenize.
9. Package.

Reference

Glover, F.A. 1985. Ultra filtration and Reverse Osmosis For the Dairy Industry. Technical Bulletin 6. National Institute for Research in Dairying, Reading, England.

• Originated in Germany in 1885; independent development in U.S. resulted in American patent in 1917 by J.L. Kraft.
• Opportunity to 'engineer' and preserve cheese products
• Stable process cheese emulsions can be made without any additives or other ingredients but it is both difficult and uneconomical

1. Process cheese must be made from cheese in which the maximum content of moisture is less than 40%. Maximum moisture is 3% more than the maximum for the cheese variety used. Minimum fat is 2% less than the minimum for the variety used. If more than one variety is used the standards are calculated on the basis of the mean standards for the varieties used.
2. Process cheese food must contain 51% cheese, not more than 46% moisture and not less than 22% fat.
3. Process cheese spread must contain 51% cheese, not more than 60% moisture and not less than 20% fat.

Cheese

• any type of natural cheese
• in U.S. and Canada, the cheese base is usually Cheddar or Cheddar types where a 3 month blend (some old cheese with young cheese for an average age of 3 months) is preferred
• frequently plants use processing as an outlet for trimmings and 2nd grade cheese but this represents a small portion of total process cheese volumes
• most Cheese used in processing is prepared especially for processing; usually stirred curd Cheddar or cheese base prepared by ultra filtration
• younger cheese is now more frequently used: flavour compensated for with spices, and Cheddar flavour preparations (e.g. enzyme modified Cheddar)
• too much young cheese gives a corky firm texture to the process cheese because with aging the proteins are broken down to shorter chains which have less interaction with each other and less elasticity, water holding capacity and emulsification capacity

Non-cheese Non Fat Milk Solids (NFMS)

• skim milk powder, whey protein concentrate (usually 35% protein), whey powder, sodium caseinate
• caseins bind water, especially sodium caseinate which is formed by reaction with emulsifying salts
• denatured whey proteins also impart water holding capacity if denaturation occurs during process cheese manufacture
• amounts of NFMS limited by texture (body) and lactose content (i.e., 15% of lactose in moisture phase will cause crystallization during cold storage.
• too much whey protein will impair meltability -- an educated guess of an upper limit is about 1.5%

Fat

• from cheese or added as cream, butter or butter oil
• cheese fat is generally present in fat globules with intact fat globule membranes
• if butter or butter oil is used artificial membranes composed mainly of casein are formed during processing
• the fat source is apparently of little consequence except for moisture considerations

Melting Salts

• also 'emulsifying salts' but not emulsifiers in the true sense
• commonly: sodium citrate, sodium aluminium phosphate (SALP), Monosodium phosphate (MSP), Disodium phosphate (DSP, Trisodium phosphate (TSP), various polyphosphates; most common are NaCit and MSP
• functional roles: chelate Ca, solubilize and disperse proteins, hydrate and swell proteins, emulsify fat, stabilize the emulsion
• emulsifier blends are designed for specific products--for example process cheese slices require a different texture than process cheese

Acid

• citric acid commonly used to adjust pH
• melting salts raise the pH or at least increase the buffer capacity of the cheese
• pH should be < 5.6 to prevent germination and growth of anaerobic spores
• the risk is probably greater with high moisture cheese spreads
• too low pH: crumbly firm texture, deemulsification
• high pH: protein bonding and solubility improve, elastic, smooth, better emulsification, more risk of germination of bacterial spores

Emulsifiers

• mono- and diglycerides may be added in small quantities but may actually interfere with emulsification by preventing protein-fat interactions

Preservatives

• Sorbic acid commonly used as mould inhibitor
• inverting jars for a minute or two after filling also helps to control mould
• by destroying mould spores in the head space

Colour

• annatto present in natural cheese such as Cheddar is not stable in process cheese
• water dispersable preparations of -Carotene are more successful

Moisture

• when heated by direct steam injection, about 10% of batch weight is incorporated as condensate for most systems
• additional moisture added as required

• Stephan cookers are commonly used: reducing, heating and comminuting in one operation
• continuous lay down cookers used for large scale production
• basic process: Cheese selection and analysis, formula calculation, trimming, shredding (reducing), blending, heating, homogenization (optional for process cheese but advised for spreads), packaging, cooling, quality control tests (pH, moisture, fat, high temp storage)

• process cheese is a medium acid food with relatively high moisture content which means that strictly speaking it should be sterilized before storing and distributing at ambient temperature
• however, the product has been "grandfathered" in and few incidents of food poisoning have been associated with process cheese products
• precautions are:

1. Use sanitized packaging
2. Make sure the pH is not more than 5.6.
3. Use phosphates in the blend of emulsifying salts to prevent germination of Clostridium spores.

Suppose a processor wishes to make process cheese food of legal composition(46% moisture, 22% fat). To allow for error he decides to set his target composition at 43% moisture and 24% fat. The ingredients on hand are Colby cheese (42% moisture, 29% fat), Cheddar cheese (39% moisture, 30 % fat), butter (16% moisture, 80% fat), whey powder (70% lactose, <1% fat, 4% moisture) and additives. Calculate the formula required for a 10 kg batch given that the weight of condensate added is 10% of the batch and the amount of cheese added is 70% of the batch of which 75% is Cheddar (75% of 70). See the composition control sheet and follow these steps:

1. Enter the final cheese composition and batch weight in the `Total' row.
2. Enter the composition of the ingredients.
3. Enter the total amounts (as percentage values) of Cheddar (75% of 70) and Colby (25% of 70) in the 'Total' column.
4. Calculate the amounts (in percentages) of fat, moisture and NSF contributed by the cheese. For example, the fat contributed by Cheddar is 30% of 52.6.
5. Calculate the percentage of fat required to bring the total fat to 24%, i.e., 24 - (5.1 + 15.8) = 3.1 and enter this value in the `Fat' column opposite 'Butter'.
6. Calculate the total amount (% of batch) of butter required (3.1 x 100/80 = 3.9) The amount of moisture (16% of 3.9) and solids-non-fat (4% of 3.9) contributed by butter can now be calculated.
7. Enter the required percentage amounts of the various additives. Calculate the amount of additional NSF required to bring the total to 33%. Enter this amount in the NSF column for whey protein concentrate. Note, any combination of whey powder, skim milk powder or whey protein concentrate can be used to adjust NSF providing the total amount of lactose is less than 15% of the cheese moisture.
8. Enter the amount of water contributed by condensate and calculate the amount of additional water required.
9. Determine the totals of each column and row to check your calculations.
10. Calculate the amounts of ingredients required per batch.

Note: The example given above is relatively simple and requires only simple arithmetic. However, consider the case where a manufacturer has quantities of high moisture cheese which he wishes to utilize in processing. He may then need to calculate the maximum amount of this cheese which can be used to replace cheddar without exceeding the legal moisture content. In this and similar cases the various unknowns must be defined in terms of required amounts of fat, NSF and moisture and the resulting equations solved simultaneously.

1. Select and analyze (moisture and fat) cheese for processing. Normally a three month blend is preferred for processed Cheddar.
2. Calculate the formula.
3. Add all ingredients into the cooker.
4. Mix thoroughly (3 min at high speed).
5. Remove a sample for pH analysis. If the pH is higher than 5.6, add more acid.
6. Blend and heat with vacuum applied to 70C. Then turn vacuum pump off and continue heating to 85C. Hold at 85C for 2 min.
7. Package process cheese hot in boxes. Spreads should be homogenized while still hot and packaged in sanitized jars.

References

Price, W.V. and Bush, M.A. 1974. The process cheese industry in the United States: A review. I. Industrial growth and problems. J. Milk and Food Technol. 37: 135 - 152. II. Research and development.Ibid 37: 179 - 198.

TABLE 20.1 Process cheese composition control: Example

TABLE 20.2 Process cheese composition control

• contributes lubrication and creamy mouth feel
• contributes flavour and acts as a reservoir for other flavours
• globules disperse light and suppress translucence making the cheese appear darker
• alteration of polar/non-polar constituents affects biochemistry
• occupies space in the protein matrix and prevents the formation of a dense matrix which produces a hard, corky cheese

• low-fat process cheese slices have been available for some time
• rubbery texture but semi-acceptable
• low-fat Cheddar at 1/3 reduction (20% fat vs 31% full fat) is semi-successful
• available in most supermarkets
• low-fat Cheddar at less than 1/3 reduction requires fat substitutes
• most successful to date are protein based beads designed to imitate fat globules
• starch is also being used to replace fat

• in order to maintain yield and avoid excessive hardness, low-fat cheese requires higher moisture
• this results in reduced salt in moisture (S/M) and increased moisture in the non-fat substance (MNFS)
• high acidity due to high moisture = high lactose retention
• may be desirable to include a washing step to leach out lactose-optimum S/M is difficult to achieve because salt greater than 2% gives a salty flavour
• typical target moistures for low fat Cheddar range from 42 - 48%
• lower moisture (near 42%) can achieve 6 - 9 month aging and may have some typical medium Cheddar flavour, but texture is hard
• higher moisture (towards 48%) gives softer texture but shorter shelf life and is often gummy

• rubbery, flaky due to lack of lubricity and tight protein matrix
• gummy, chewy
• bitterness in cheese is caused by hydrophobic (fat soluble) peptides (protein fragments) which result from curing--the amount, or at least the perceived amounts of these peptides, is increased in low-fat cheese, perhaps because these hydrophobic peptides are normally absorbed by the fat and are more available for tasting in low fat cheese
• certain cultures have the ability to further break down these peptides and reduce bitterness so that bitterness in low-fat cheese often peaks after a few weeks and then decreases with further ripening
• astringency is common in low fat cheese--it is distinct from bitterness but often confused with bitterness--it is not detected by the taste buds but rather a textural/physical perception at the back of the mouth ---related to interaction of saliva with cheese components, probably certain peptides
• meaty/brothy flavour is typical of low fat cheese--this is also related to interaction of amino acids (from protein breakdown) with alpha-dicarbonyls
• unclean flavours related to non-starter bacteria are more pronounced in low fat cheese--this can be reduced by micro-filtration to remove most bacteria before cheese manufacture
• increased gas formation probably due to non-starter bacteria encouraged by low S/M causes slits---again could be controlled by micro-filtration

General Principles

• adjust each stage to include more moisture
• keep pH higher at each stage relative to normal cheddar

Standardization

• standardize to obtain about 35% FDM or about 20% fat in the cheese assuming 45% moisture

Pasteurization

• normal is recommended
• may be some advantage in higher temperature to denature whey proteins and increase moisture retention

Culture

• normal level recommended

Calcium Chloride

• recommended especially if higher pasteurization temperatures used

Cutting

• larger than normal cheddar to promote more moisture retention

Cooking Temperature

• lower than normal, 37C

Draining

• high pH, near 6.4
• shorter cooking time

Stirring Out

• none

Washing

• may be necessary for high moisture cheese to reduce lactose content

Salting

• normal, about 2.5% of expected yield

Curing

• normal temperatures
• shorter time, especially for high moisture

• three methods:

1. Chemical extraction with Beta-cyclodextrin
2. Extraction with Supercritical carbon dioxide--90% removal
3. Steam extraction--75% removal

• problem is that all procedures require separation of butter oil, with subsequent milk recombination
• necessity of homogenization makes cheese making difficult

See Figure 5.1 and Membrane Processing in the Dairy Science and Technology Education website.

Reverse Osmosis (RO).

A pressure driven process where small molecules (molecular weight less than 100 daltons, eg., water) are separated from larger molecules by a semi-permeable membrane. In practice the term describes a concentration process where water is removed to increase total solids content of a liquid. For example desalination can be accomplished using (RO). It is appropriate to think of RO and the related membrane processes, UF and nanofiltration, as chemical filters where the separation characteristics are determined by the pore size of the membrane and the chemical interactions between the product and the membrane. The most common RO membrane material is cellulose acetate with operating pH of 5 -7. Dairy applications include supplementation of milk evaporators, whey concentration, and waste treatment.

Ultra filtration (UF). 

A membrane process similar to RO where semi-permeable membranes are used to separate large molecules (molecular weight greater than 10,000) such as proteins from small molecules such as sugars. Common membrane materials are polysulfone (operating pH 2 - 12) and ceramic (pH 2-12, retort sterilizable).

Nanofiltration. 

A membrane process with separation characteristics intermediate between RO and UF. It is designed to separate small minerals and ions from larger molecules such as sugars. It is used to demineralize cheese whey as an alternative to ion exchange and electrodialysis processes.

Microfiltration. 

A membrane filtration process designed to separate particles greater than .2 µM. Principal dairy applications are spore removal from milk to prevent late gas defect in cheese and to extend the shelf life of pasteurized milk.

Permeate and Retentate. 

Material passing through the membrane is permeate while material retained by the membrane is retentate. For example UF milk permeate is composed of water, sugar, some minerals and non-protein nitrogen compounds. UF retentate is a concentrate of milk fat and protein, including both caseins and whey proteins.

Component processing. 

Developments in membrane processing combined with other conventional and emerging technologies make it possible to isolate and recombine milk components in new ways to produce new products, process conventional products more efficiently, or reduce waste.

Countries most active in the study of the properties and processing of UF milk retentates are France, U.S.A., Holland, England and Australia. The earliest and currently the largest dairy application of UF is in the production of functional (i.e., undenatured) whey protein concentrates. Reverse osmosis is also used in whey processing.

Potential benefits of membrane processing are:

Reduced Farm Feed Costs. Permeate which could be removed at the farm contains lactose, minerals and some nitrogen.

Cheese Manufacturing Costs. Reduced cooling and heating costs, lower rennet needed, reduced capital equipment costs, and increased yield from better retention of whey proteins in the cheese.

Transportation Costs. On farm UF would reduce milk volume by a factor of at least 2, and UF-thermized milk could be picked up less frequently

Economic Benefits to the Farmer of performing UF on the farm, are savings in both transportation and feed costs and the opportunity to market a value added product.

Product Standardization. It is possible to standardize the protein, fat and non-fat solids of all dairy products. For example fluid milk is now skimmed to a legal minimum of 3.25% fat so that on average about 6.0 kg of fat is removed per 1,000 kg of milk. UF makes it possible to skim protein in the same way as we now skim fat. This practice will be increasingly attractive as the value of milk protein relative to milk fat increases.

New Products. New cheese varieties, dairy spreads, high protein milks, milk based meal supplements. 

Composition. 

UF retains all milk fat and protein. Lactose permeates freely through the membrane. Mineral retention is dependent on the association with proteins and decreases with acidification.

Physical Properties. 

Fat globules are slightly reduced in size, indicating that some homogenization takes place in the UF system. Casein micelles and whey proteins are unaltered. Buffer capacity of UF retentates increases exponentially with total solids due to the concentration of proteins and salts

Lactic Fermentation.

Culture growth is normal but more acidity is required to reduce pH because of the high buffer capacity of UF milk retentate..

Rennet Coagulation. 

If rennet is added proportional to milk volume rather than weight of protein, rennet coagulation time (RCT) is unaffected by UF concentration. This means that, relative to the amount of protein present, less rennet is required for coagulation. However, the structure and properties of the gel are quite different than in normal milk, and for aged Cheese there is insufficient rennet to promote ripening. Concentration by UF has the remarkable effect of restoring rennetability to over pasteurized milk.

Milk Quality.

UF activates the natural milk lipase and concentrates bacteria. However, UF retentates have superior freeze-thaw stability, less oxidative rancidity, and have greater microbiological stability.

MMV Process. (Maubois et al., 1969) Concentrate to 5 - 7 x original milk protein content, add both starter and rennet, incubate until both coagulation and lactic fermentation are complete, and ripen. MMV is most successful for some fresh and soft-ripened cheese varieties which have relatively low total solids and do not require rigorous pH control. It has been most successful for Feta cheese. The chief difficulty is that the MMV process produces close textured cheese which has led to two types of Feta: (1) Structured or conventional Feta and; (2) UF or cast Feta. The MMV process can also be used to manufacture cheese base to extend young Cheddar in process cheese formulations. The amount of UF retentate in process cheese products is limited by the presence of whey protein in the retentate which impairs meltability of the cheese.

The LCR Process. LCR stands for low concentrated retentate. Milk is concentrated 1.5 - 2 x original milk protein content. Cheese is made using minor modifications to traditional procedures. LCR is now the principal process used in French Camembert providing the advantages of slightly higher yields, labour savings, facilitation of continuous cheese making, and increased plant capacity. Most types of hard cheese have been made by LCR principles with varying degrees of success.

UF retentates in the mid range of concentration (2 - 5 x original protein content) have not been successful with the possible exception of Feta. It is possible to produce higher yields of Feta than via conventional means by heat treating retentate at sufficient levels to denature whey proteins. Normally this would impair rennet function, but UF treatment restores rennetability. The result is that denatured whey proteins are incorporated into the rennet gel, thus increasing cheese yield. This permits manufacture of a structured Feta, similar to traditional products, while realizing significant yield improvement. This practice has been successful for Feta but not for most rennet cheese because the whey proteins impair meltability and produce a coarse textured cheese.

TABLE 22.1 Ultrafiltration of whole milk. Typical composition of concentrate and permeate System: polysulfone membrane in tubular configuration, small pilot plant, batch operation at 50C (Glover, 1985).

• cost
• functionality
• cholesterol
• saturated fats
• shelf life
• real or perceived?
• nutritional equivalency

• dairy manufacturers in US believe the effect of substitutes is additive
• use as extenders lowers price and increases consumption
• some use substitutes for dietary reasons
• it is the dairy companies producing substitutes not other food manufacturers

• Cheddar - most popular
• Mozzarella - industrial purposes, 60% used in pizza
• Swiss
• Colby
• Gouda
• Provolone
• Process
• Cream Cheese
• Cheese Spreads

Filled Cheeses

• Skimmed milk and vegetable oils or blends of butter and vegetable oils
• Unpopular because must work with low solids raw material

Cheese Analogues 

Synthetic: soya protein

soya oil

stabilizer/emulsifier

flavour

Partial Dairy: casein

soya oil

stabilizer/emulsifier

flavour

Dairy: casein

butter oil

stabilizer/emulsifier

Typical Formula

Process

1. Melt the fat (eg., a partly hydrogenated coconut oil of melting point 37C) raise the temperature to 70C.
2. Add the stabilizer system. Proprietary blends are available from several suppliers.
3. Blend the water into the oil with rapid agitation to form an emulsion.
4. Slowly, add the calcium caseinate to the oil/water emulsion while the temperature is maintained at 70C. Then, blend in the sodium caseinate. Cheese texture will be begin to develop.
5. Blend in Cheddar cheese and salt and then add the enzyme-modified cheese flavour.
6. Add the acid together with a little annatto for colouring. The drop in pH has a dramatic effect on texture development.
7. Fill moulds, cool to 5C and store overnight for flavour equilibration.