164 Milk and Its Products. 



casein, coagulation may be brought about by several 

 reagents, but the one universally employed in cheese 

 making is a soluble ferment found in the stomachs 

 of young mammalia and in certain other animals, 

 known as rennet. By the addition of rennet to 

 milk, the casein takes on the form of a homogene- 

 ous gelatinous solid, and in changing its form en- 

 closes in its mass the globules of fat. In bringing 

 about the change in the casein in this way, the ren- 

 net acts by contact ; that is, its own constitution is 

 in no way disturbed, and a minute amount of rennet 

 is capable of causing the coagulation of a large 

 amount of milk. 



Quality of miU' for cJieese mal'nig. — While it is 

 scarcely necessary to demonstrate that milk is val- 

 uable for butter making in proportion to the amount 

 of fat it contains, the proposition that its percent- 

 age of fat is also a measure of the value of nearly 

 all milk for cheese making has not been so readih^ 

 accepted. Indeed, until within a very short time, the 

 prevailing opinion among dairymen and cheese -makers 

 has been that a milk poor in fat was likely to be 

 rich in casein, and hence more valuable for cheese 

 making purposes. But both fat and casein are con- 

 stituents of cheese, and both are of nearh* equal im- 

 portance ; hence, the richer a milk is in fat, the 

 more cheese it will make, and recent research has 

 shown that for milks containing a normal amount of 

 fat the yield of cheese will be nearly proportional to 

 the percentage of fat in the milk. 



