Section E: Manufacture, Ripening, Process Control and Yield Efficiency

Cheese making step by step

This chapter describes the principal steps involved in cheese manufacture.

Ripening the Milk

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.

Setting the Vat

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.

Cutting The Curd

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%.

Cooking

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.

Draining

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.

Washing

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.

Curd Handling

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

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.

Salting

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%. 

Ripening and packaging

Ripening processes: chemical and physical changes

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.

Principal Ripening Agents

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 for Optimal Curing

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.

Temperature of Curing

  • 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. 

Humidity of Curing

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

Ripening Treatments

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.

Packaging

  • 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.

Process Control

This Chapter will not be discussed during the short course lectures because most of its contents are covered in other Sections or in the cheese make procedures. It is included here as a summary of important process control principles.

The Objectives of Cheese Manufacturing

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.

Moisture Control

  • 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

pH Control

  •  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. 

Mineral Control

  • 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.

Texture Control

  •  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.

Flavour Control

  • 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

Yield efficiency

Distribution of Components During Cheese Making

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

Factors Affecting Yield

  • 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.

Principles of Yield Optimization

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.

Yield Control

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.

Recovery of Milk Components

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.

Yield Prediction

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.