Purposes of Calculating Predicted Yields
- Provide a target against which to judge actual yields and determine mass balance within the plant
- Flag errors in measurement: eg. weights of milk or improper standardization etc.
- 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.