CHEESE 209 



properly set, it is cut into small pieces for the purpose of 

 facilitating the expulsion of the whey. With the develop- 

 ment of acid, a certain action is exerted on the casein, which 

 causes the pieces of curd to adhere to each other, and to fuse 

 into one mass under the influence of the pressure exerted in 

 the press in which the curd is placed after the whey has 

 been largely removed. Bacterial growth in the curd occurs 

 rapidly, the colonies developing in a manner similar to those 

 obtained in the plate cultures of the bacteriologist. 



The rennet used also contains the digestive enzyme of 

 the stomach juice, pepsin, which can exert its action only 

 in the presence of an acid. In the stomach of an animal, 

 the hydrochloric acid secreted by the stomach wall is the 

 activating agent, while in the cheese the lactic acid formed 

 in the acid fermentation of the sugar gives favorable con- 

 ditions for action. The protein of the cheese is changed 

 into soluble decomposition products similar to those formed 

 in the stomach digestion of nitrogenous compounds. The 

 acid reaction established by the lactic bacteria serves to 

 protect the cheese from the action of the putrefactive bac- 

 teria that are always present, in the same manner as the 

 acid of silage protects it against putrefaction. It is evi- 

 dent that without the lactic bacteria the cheese will either 

 remain in the same condition in which it is when removed 

 from the press, or else it will undergo putrefaction. It is 

 also evident that without the bacteria the manufacture of 

 cheese would be impossible. 



Gassy cheese. If the milk is handled in such a way as 

 to allow the colon or gas-forming type of bacteria to over- 

 come the usual lactic type, the quality of the cheese will 

 be injured, owing not only to the impairment of the flavor 

 by the by-products of these organisms, but the texture of 

 the cheese is rendered open or porous by the development 

 of gas which permeates the mass of the cheese. 



