98 MILK PRODUCTS 



is meant the protein as it exists in milk, or as 

 precipitated from milk by acids. When milk 

 is coagulated by rennet, only a part of the 

 proteins enter into the curd ; true casein contains 

 about 15.7% of nitrogen, but the protein matter 

 of cheese contains about 14.3%. Under the 

 process of ripening this is further decomposed, 

 amino- and ammonium compounds, peptones 

 and albumoses being formed. 



The following figures, obtained by Van Slyke, 

 will serve to give some idea of the extent to which 

 the curd is changed in ripening. The figures 

 represent average percentage on the total nitrogen. 

 The cheese was an American cheddar: 



Green After Five 



Cheese Months 



Soluble nitrogen compounds ... 4 . 23 35-52 



Soluble amino compounds none 11 .66 



Soluble ammonium compounds none 2.92 



Van Slyke's experiments seem also to indicate 

 that the cheese ripened more rapidly when the 

 curd was precipitated by a larger quantity of 

 rennet and, especially, that cheese rich in fat 

 ripened more rapidly than skim-milk cheese. 



In addition to the fat and nitrogenous com- 

 pounds just mentioned, cheese may contain a 

 small amount of lactose and of lactic and other 

 organic acids. There is present also a certain 

 proportion of mineral matter, alkaline and earthy 



