CHEESE 



Cheese is a ripened product made from milk. The ripen- 

 ing process is carried on by different groups of micro-organisms 

 which cause a series of chemical changes. Some groups produce 

 proteolysis of the casein and decomposition of the fat and milk- 

 sugar. Flavor in cheese is also the result of these activities. The 

 collective work of these groups of micro-organisms is very com- 

 plex, and the results of their combined action are different from 

 the sum of the individual group activities. Green cheese contains 

 casein, fat, water, and the salts of milk, and for a short period 

 milk-sugar is present. 



The chemical changes in cheese are more complex than those 

 in butter. In butter there is acid and aroma formation which 

 determines the quality of butter, but there is not the essential 

 variation in butter that there is in types of cheese. The micro- 

 flora in butter is simple when compared with that of cheese. The 

 aroma of butter is due to the activity of certain bacteria, and, 

 similarly, the type of cheese is determined by the kinds of micro- 

 organisms which are concerned in the ripening process. It was 

 formerly beheved that the different types of cheese were merely 

 the result of differences in manipulation, as some were pressed 

 more vigorously than others, causing a variation in the amount 

 of water, and as the ripening temperature varied with the dif- 

 ferent kinds of cheese. Of course the influence of varying ma- 

 nipulations was learned by experience, but it is now known that 

 they have bearing on microbial Ufe. Conditions of ripening are 

 made suitable for the particular type of cheese. 



Cheeses may be divided into two groups, namely, sour milk 

 and rennet cheeses. Sour milk cheeses are made from sour milk 

 by precipitating the curd from the milk in a cheese kettle over 

 gentle heat. They are always soft and the fresh precipitate consists 

 chiefly of casein. When rennet is used for precipitating the curd, 

 less acid is required than for the preparation of sour milk cheese. 

 Rennet cheeses may be soft or hard, and their coagulum consists 

 chiefly of paracasein. The consistency of the curd is determined by 

 the amount of whey that remains, the type of cheese varying from a 

 consistency so hard that the cheese is difficult to cut to one very 

 soft or even semifluid. In hard cheese the ripening process proceeds 

 more or less uniformly throughout the mass, while in soft cheese 

 ripening commences from the outside. The surface of soft cheese 

 is covered with micro-organisms which produce characteristic 

 changes in the curd, and enzyms secreted by these micro-organ- 



611 



