Bacteria and Cheese Making. 181 



the salt gradually diffuses quite uniformly through the 

 cheese. The method of salting has apparently a marked 

 influence on the ripening process, since if the salt is 

 added in the same way, and in amounts used in the 

 cheddar process, the flavor will not be that of a Swiss 

 cheese but will resemble a cheddar. 



In cheddar cheese, the whey is expelled from the curd 

 by means of the acid which is developed in the curd, and 

 by heating the curd to a temperature of 95 F. to 100 

 F. In Swiss cheese the development of acid during the 

 making process is prevented, because of the smaller num- 

 ber of acid-forming bacteria in the milk; other factors 

 must therefore contribute to the expulsion of the whey 

 to secure a firm curd. This is accomplished by cutting 

 the curd into very small pieces and by briskly stirring 

 it during the making, heating it during this process for 

 a period of 20 to 30 minutes at 130 to 140 F. It might 

 be thought that this high temperature, which is approx- 

 imately that used in pasteurizaion would destroy the 

 acid-forming bacteria, but these are apparently pro- 

 tected as they are within the curd. During the time the 

 cheese is being pressed, the contained bacteria begin to 

 grow and the whey coming from the cheese toward the 

 end of the pressing shows a high acidity. If it does not 

 show such a development of acid, the maker has reason 

 to believe that the cheese may never ripen in a typical 

 manner. 



It has been mentioned that the milk contains but few 

 acid-forming bacteria. The maker, however, attempts 

 to insure the presence of a sufficient number by the use 

 of "home-made" rennet. This is prepared by placing 

 a piece of dried rennet, i. e., the stomach of the calf, in 

 whey, keeping the same in a warm place for twenty- 



