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.