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 
