CREAM-RIPENING. 213 



it a tryptic ferment, because it is similar in its action to the 

 trypsin produced by the digesting glands. The putrefactive 

 germs ordinarily act upon the nitrogenous matter of cream, 

 as described above. 



2. The milk-sugar in cream is present in a perfect solution, 

 and consequently it is thought that bacteria are able to utilize 

 it as food directly. The typical lactic-acid-producing germs 

 cause the milk-sugar to split up into lactic' acid chiefly, accord- 

 ing to the following equation: 



Milk-sugar. Lactic acid. 



There are a number of germs which are able to produce 

 lactic acid from milk-sugar, but practically all of them, so far 

 as known, produce other by-products besides the lactic acid. 

 Some germs produce much lactic acid and a small amount of 

 other by-products, while other germs produce little lactic acid 

 and large amounts of several other by-products. Some of them 

 break up the milk-sugar and change it into lactic acid and car- 

 bonic gas. Other species produce lactic acid and alcohol. 

 This latter species Grottenfelt claims to be closely associated 

 with the production of flavoring substances in butter. Different 

 kinds of gases, such as nitrogen, hydrogen, carbonic-acid gas, 

 and marsh-gas are also formed. 



It is doubtful whether there are any germs which are able 

 to transform milk-sugar entirely into lactic acid. If such were 

 the case, 1 gram of milk-sugar would produce 1 gram of lactic 

 acid. According * to some experiments carried on by one of 

 the authors, .8 of a gram was the maximum amount of acid 

 developed from 1 gram of milk-sugar, and .5% is the average 

 amount of acid developed from 1 gram of milk-sugar. In the 

 experiments, efforts were made to have the typical lac tic- acid 

 ferments present in the cream. The following table may prove 

 of some interest : 



* Chemical Changes during Cream Ripening. (Thesis I. S. C.) 



