BACTERIA JN CHEESE 225 



it tends to become. Dry cheeses are always hard, and even the 

 soft cheeses may be hard after they become dry. 



The chemical changes which occur are very profound. The 

 first to occur is, in most cases, the development of lactic acid, 

 and in nearly all, if not all, types of cheeses this souring is 

 necessary for the subsequent steps. After the acidity develops 

 the changes go on very much more slowly; but they usually 

 consist of a gradual reduction in the amount of acidity until 

 finally the cheese may become slightly alkaline. At the same 

 time the casein is undergoing a series of changes by which it is 

 gradually reduced from the condition of a raw proteid (casein) 

 to the condition of peptone or proteoses, which are similar 

 products. Proteids are, as a rule, insoluble in water, but after 

 they have been converted into peptones or proteoses, the prod- 

 ucts are soluble. This change is essentially similar to that 

 occurring in the digesting of the proteids in the stomachs of 

 animals, and the changes in the ripening of cheese are very 

 similar to those of digestion. For this reason a ripened cheese 

 is to be looked upon as an already digested food. With several 

 of the soft cheeses, like the Brie and Camembert, the digestion 

 is very complete, and the ripened cheese is an almost wholly 

 predigested product. Such cheeses are very easily handled by 

 the digestive organs and form a very easy assimilable food. 

 The extent to which this breaking down of the casein into 

 soluble products occurs varies very much in the different types 

 of cheeses. In the hard cheeses it is less complete than in the 

 softer ones; and in the latter class the change may be so great 

 as to reduce the casein largely into soluble products. The 

 change also varies with the age of the cheese, for it is a 

 phenomenon that progresses week by week as the cheese ripens 

 and does not become complete until the whole process is finished. 

 This general process is commonly called digestion. 1 



iVan Slyke and Hart. Ann. Rep. N. Y. Exper. Sta., 1903. 

 Van Slyke and Hart. Bui. 261, N. Y. Exper. Sta., 1905. 

 Harding. Bui. 237, N. Y. Exper. Sta., 1905. 



