BACTERIA IN CHEESE 23! 



is neutralized by the presence of some alkaline, like carbonate 

 of soda, the bacteria continue to grow, and eventually produce 

 the peptonization of the casein. Moreover, he was able to show 

 that the grade of the cheeses is very closely dependent upon the 

 growth of lactic bacteria. He found that certain types of lactic 

 bacteria, inoculated into the cheese, resulted in a fine grade of 

 cheese, while others resulted in a poorer product. He found, 

 also, that cheeses from which lactic acid bacteria were excluded 

 by aseptic milking would not ripen normally, while they would 

 do so if the acid germs were present. 1 All of these facts to- 

 gether led him to the conclusion that it is this peptonizing 

 power of the lactic acid bacteria, under certain conditions, 

 which is responsible for the chemical changes that take place 

 in the ripening cheese. 2 This conclusion, however, has not been 

 very generally accepted; for while others have confirmed his 

 conclusion that the lactic acid bacteria under these conditions 

 do produce a certain amount of peptonization of the casein, the 

 action is extremely slow and not very complete, and it has not 

 seemed to most chemists that the phenomenon in question is 

 sufficiently explained by this slow action of the lactic acid bac- 

 teria. The bacterial explanation of the ripening has been thrown 

 into uncertainty by Babcock and Russell, who showed that 

 cheeses, if kept in a vapor of chloroform, which will prevent 

 bacteria growth entirely without checking the action of the 

 enzymes, will undergo the chemical changes of ripening, al- 

 though they will not acquire the desired flavor. 



As a result, a third theory has been advanced that the chem- 

 ical changes of digestion are due to the action of the enzymes. 3 

 These enzymes are always present, some in the original milk 

 and some added with the rennet, and it is only natural to sup- 

 pose that during the long period of ripening they will carry on 



1 Freudenreich. Land. Jahr. d. Schweiz, 1902. 



2 Jensen. Milch. Zent., II., p. 393, 1906. 



3 Babcock, Russell and Vivian. 17. Ann. Rep. Wis. Exper. Sta., 1900. 

 Jensen. Landw. Jahr. d. Schweiz, 1900. 



