164 Dairy Bacteriology. 



ciate the selling value of the entire product several cents 

 per pound. 



The tests that have been previously described (p. 105) 

 have been devised especially for testing the quality of 

 the milk for cheese making purposes, and are of the 

 greatest service to the maker in tracing the source of 

 poor milk. 



Cheddar cheese. The first step in the making of 

 cheddar cheese is the "ripening" of the milk, or the de- 

 velopment of a small amount of acid. In this fermenta- 

 tion, the development of acid is preceded by an enor- 

 mous increase in the number of acid-forming bacteria. 

 Milk for cheese making should show an acidity of about 

 0.2 per cent or slightly more than in fresh milk. In 

 other words, the maker wishes the milk to be in such 

 condition, bacteriologically, that if kept at a tempera- 

 ture favorable for the growth of the acid-forming bac- 

 teria, the acidity will increase rapidly. 



The curdling of the milk to precipitate the cheese 

 solids is produced by the addition of rennet, which is 

 obtained by extracting the fourth stomach of the young 

 calf with a solution of common salt. In the past the 

 maker prepared his own rennet solution from the dried 

 ^ stomachs ("rennets"), but at present, the extract is pre- 

 pared commercially, in a much more uniform manner. 

 The rapidity of the curdling is dependent upon the acid- 

 ity of the milk. In order to secure proper rennet action, 

 a slight increase of acid over that found in fresh milk is 

 usually necessary; thus at the very beginning of the 

 process of making cheddar cheese, the bacteria are of im- 

 portance. 



As the milk curdles, the bacteria are enclosed in the 

 curd as are the fat globules. The curd is cut into small 



