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%.