Important parameters of composition
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).