Conversion of milk to cheese curd

Typically, five steps, or groups of steps, are involved in the conversion of milk to cheese curd coagulation, acidification, syneresis (expulsion of whey), moulding/shaping and salting. These steps, which partly overlap, enable the cheesemaker to control the composition of cheese, which, in turn, has a major influence on cheese ripening and quality. 

Enzymatic coagulation of milk. The enzymatic coagulation of milk involves modification of the casein micelles via limited proteolysis by selected proteinases, called rennets, followed by calcium-induced aggregation of the rennet-altered micelles  

As discussed in Chapter 4, the casein micelles are stabilized by K-casein, which represents 12-15% of the total casein and is located mainly on the surface of the micelles such that its hydrophobic N-terminal region reacts hydrophobically with the calcium-sensitive a i-, ix 2 8-caseins while its hydrophilic C-terminal region protrudes into the surrounding aqueous environment, stabilizing the micelles by a negative surface charge and steric stabilization. 

Rennets. The traditional rennets used to coagulate milk for most cheese varieties are prepared from the stomachs of young calves, lambs or kids by extraction with NaCl (c. 15%) brines. The principal proteinase in such rennets is chymosin about 10% of the milk-clotting activity of calf rennet is due to pepsin. As the animal ages, the secretion of chymosin declines while that of pepsin increases in addition to pepsin, cattle appear to secrete a chymosin-like enzyme throughout life. 

The gene for calf chymosin has been cloned in Kluyveromyces marxianus var. lactis, Aspergillus niger and E. coli. Microbial (cloned) chymosins have 

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C. Cheese Science and Technology Composition and Constituents of Milk Conversion of Milk to Cheese Curd... 

The conversion of milk to cheese curd essentially involves coagulating the casein, either isoelectrically or enzymatically if present, the milk fat is occluded in the curd. The mechanisms of rennet and acid coagulation of casein and the subsequent manipulation of the coagula to produce cheese curd are described in the following sections. 

The conversion of milk to cheese curd is only the first stage in the production of most cheese varieties. Essentially all hard and most soft cheeses are ripened for periods ranging from a few weeks to 2 years or longer. During this period, cheeses undergo numerous biochemical changes which lead to the development of the appropriate flavor and aroma. The... 

The production of rennet-coagulated cheeses can, for convenience, be divided into two phases (1) conversion of milk to curds and (2) ripening of the curds. 

Whey is the liquid obtained by separating the coagulum from milk, cream, and/or skim milk in cheese making. Whey obtained from the process in which a significant amount of lactose is converted to lactic acid or obtained from the curd formed by direct acidification of milk is known as acid-type Whey. Whey obtained from the process in which there is insignificant conversion of lactose to lactic acid is known as sweet-type Whey. The acidity of Whey may be adjusted by the addition of safe and suitable pH-adjusting ingredients. The final product is pasteurized and is available as a liquid or dry product. 

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