212 BUTTER-MAKING. 



of ripemng are not due to any instability of the components 

 of cream, nor are they attributed to any of the enzymes. 

 Galactase is a pre-existing enzyme in milk; consequently it 

 would be present in cream, but present only to a very small 

 extent. If it were possible to exclude from the cream all the 

 different kinds of bacteria, ripening would not take place. 

 At least it would proceed at a much slower rate than the 

 ordinary rate of change in the ripening of cream ; this proves 

 that the soUds of cream are chemically stable and that the 

 enzymes or unorganized ferments play only a secondary part 

 in bringing about the different changes in cream ripening. 

 There are two classes of solids in cream which are decom- 

 posed chiefly during ripening: viz., (1) Albuminoids, and (2) 

 Sugar. 



1. Most authorities maintain that bacteria are unable to 

 feed on, or to decompose directly any substance which is not 

 present in the form of a solution. As casein is not normally 

 present in a solution in milk, the pre-existing enzymes or 

 bacterial by-products must cause the first decomposition of 

 casein before the germs are able to utihze it. The by-products 

 resulting from the casein ferments are many, and very com- 

 plex. According to Russell * albumoses, leucin, peptone, 

 tyrosin, and ammonia are formed. Freudenrich claims that in 

 addition to these butyric acid is a by-product. Besides these 

 substances, gases such as carbonic gas, marsh-gas, and nitrogen 

 are formed- Whether all these by-products are formed directly 

 or indirectly or both, no one knows for certain. 



The typical ferments seem to act similarly upon the casein 

 in milk. They produce first a rennet-like ferment, which 

 curdles the milk. After it has been curdled, the curd is digested 

 or peptonized by the action of some enzyme. The casein in a 

 sample of milk containing a preponderance of casein ferments 

 will in a few weeks, or even less time, disappear entirely. Ap- 

 parently the milk has been transformed into whey. This 

 particular ferment is called casease by Duclaux. Conn calls 



* Dairy Bacteriology. 



