212 BUTTER-MAKING. 
of ripening 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 solids 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 utilize 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. 
