232 PRACTICAL DAIRY BACTERIOLOGY 



the peptonizing of the casein, which is their distinctive char- 

 acteristic. 1 The conclusion regarded as most probable to-day, 

 therefore, is that the chemical changes, whereby the caseins 

 are broken down to peptones and proteoses, are due to enzyme 

 action rather than to bacteria, and the enzymes that produce 

 the action are 'partly present in the original milk (galactase), 

 and partly added to it with the rennet, which is used to curdle 

 the milk (pepsin). 2 



Flavors. The source of the cheese flavor is even more un- 

 certain than that of the chemical action. The peptones and 

 proteoses, which are obtained by the enzyme digestion of the 

 caseins, do not possess any noticeable flavor, and certainly do 

 not show any trace of cheese flavor. The digestion of the 

 casein, which may have been produced by the enzymes present, 

 will not result in the flavoring of the cheeses. Moreover, the 

 cheeses ripened in chloroform vapor, which allows the enzymes 

 to act, but prevents bacteria from growing, though they ripen, 

 do not develop flavors." These flavors must be due to some 

 other cause than enzyme action. That they are the end product 

 of chemical decomposition seems to be extremely probable. In 

 many cases, they are associated with ammonia; and ammonia, 

 as is well known, is one of the final products of proteid destruc- 

 tion. It is generally believed that these end products are the 

 result of the action of bacteria or some other micro-organisms. 

 The only known agency that commonly produces the complete 

 destruction of proteids is bacteria, and while the matter has 

 never been put to any satisfactory test, the most probable ex- 

 planation seems to be that these cheese flavors are the result 

 of the final bacterial decomposition. 



Against this view, however, has been urged the fact that in 



*Van Slyke, Harding and Hart. Bui. 203, N. Y. Exper. Sta., 1901. 



2 Marcas and Huyge. Rev. Gen. d'Lait, vi., p. 27, 1906. 



3 Van Slyke and Hart. Bui. 231, N. Y. Exper. Sta., 1903. 

 Harding. Bui. 237, N. Y. Exper. Sta., 1903. 



Van Slyke, Harding and Hart. 20. Ann. Rep. Wis Exper. Sta., 1902. 



