CHEESE 365 



manufacture. The ripening process appears to be a 

 peptic proteolysis at first ; later, when less acid or more 

 alkaline conditions prevail, it resembles tryptic digestion. 

 Although galactase and the pepsin of rennet are 

 probably concerned in some degree with the ripening 

 of cheese, it is to bacteria that the chief cause must 

 be attributed. Various kinds of organisms are present 

 in the milk as it comes from the teats of the cow, or 

 find their way into it from the air and utensils of the 

 stable and dairy. With the rennet large numbers are 

 added, since each c.c. of the extract ordinarily used contains 

 from 25 to 35 millions of bacteria. 



Many elaborate investigations have been undertaken 

 to ascertain the number and kind of bacteria present in 

 cheeses at various stages in the ripening process. It 

 is usually found that in the fresh curd there are fewer 

 bacteria than in the slightly acid milk from which the 

 curd has been precipitated by rennet, large numbers being 

 of course removed in the whey. According to Russell 

 and Weinzirl, in a new Cheddar cheese there is a decrease 

 in the bacterial content during the first twenty-four to 

 forty-eight hours, due apparently to a reduced temperature 

 and to a further loss of whey in the press. From this 

 point a rapid rise in numbers takes place until a 

 maximum is reached, when a gram of cheese will contain 

 from 90 to 150 millions or more of bacteria. The time 

 taken for the development of the maximum number of 

 organisms depends upon the kind of cheese, the tempera- 

 ture at which it is kept, and other factors ; in Cheddar 

 it usually occurs between the tenth and twentieth day. 

 A steady decline in numbers now goes on for several 

 weeks or months until the cheese contains comparatively 

 few living organisms. By microscopic examination of 



