256 THE BOOK OF CHEESE 



expulsion of the whey, (c) The acid so changes the nature 

 of the curd as to cause ' matting/ or ' cheddaring ' 

 of the curd, (d) The acid activates the pepsin of the 

 rennet extract, (e) The acid prevents the growth of 

 putrefactive bacteria in the cheese. (/) It has been shown 

 that Bacterium lactis acidi is able to form acid in the ab- 

 sence of the living cell, (g) The development of Bacterium 

 lactis acidi is followed by the growth of another group of 

 acid-forming bacteria, the Bacillus Bulgaricus group. 

 They reach numbers comparable with those of the first 

 group, reaching their maximum number within the first 

 month of ripening. Since they develop after the fermenta- 

 tion of the milk-sugar, they must have some other source 

 of carbon and of energy than milk-sugar." It is also prob- 

 able that other groups constantly present contribute to 

 the changes. 



From the preceding discussion it is evident that each 

 of the ripening agents has its important part to play in 

 the ripening process and a normal ripening of the cheese 

 is a composite result of these various agencies. 



239. Conditions affecting the rate of cheese ripening. 

 -The rate at which these agents cause ripening of the 



cheese depends on several factors. 1 Most of these factors 

 are within the control of man. They are as follows : the 

 length of time ; temperature of the curing-room ; moisture- 

 content of the cheese ; size of the cheese ; the quantity of 

 salt used ; the amount of rennet ; the influence of acid. 



240. The length of time. The water-soluble nitro- 

 gen compounds increase as the cheese ages, other 

 conditions being uniform. The rate of increase is not 



1 Van Slyke, L. L., and E. B. Hart, Conditions affecting 

 chemical changes in cheese ripening, N. Y. (Geneva) Exp. Sta. 

 Bui. 236, 1903. 



