RELATION OF MICROORGANISMS TO CHEESE 489 



Bact. lactis acidi to the milk, the proportion of desirable bacteria can 



be increased and a partial control of the fermentation thus secured. 



TESTS FOR THE QUALITY OF MILK. Methods by which the cheese 



maker can determine, in a rough manner, the kinds of bacteria present 



FIG. 147. The type of curd obtained from milk in which the acid-forming flora 

 consists almost wholly of Bact. lactis acidi. No gas holes and no marked mechanical 

 holes as the curd has "matted" almost perfectly. (Original.) 



have been devised. The bacteria most dreaded and most frequently 

 present are those of the B. coli-aero genes group. 



The method most frequently used for their detection consists in 

 incubating a sample of the milk to be tested at temperatures ranging 

 from 35 to 40 for a few hours and noting the type of curd that is 

 formed. Milk suitable for cheese making should show the solid curd 

 characteristic of the Bact. lactis acidi group, while gassy curds or soft 



