CHAPTER IV. 
FERMENTS IN MILK. 
Definition.—The changes which milk undergoes by standing 
at a suitable temperature are called fermentations. The 
causal agents are called ferments. There are two kinds of 
ferments in milk; viz.: (1) the organized, and (2) the unorgan- 
ized. The latter includes the enzymes. So far as known, only 
one pre-existing enzyme is found in milk. This one was dis- 
covered by Russell and Babcock. They named it galactase. 
It is a tryptic ferment. This galactase is present to such a 
small extent in milk that it exercises very little influence upon 
the characteristics of milk. If the milk were rendered entirely 
sterile or free from organized ferments, the fermentative changes 
would proceed at an unusually slow rate. The galactase has 
been suggested to be of some importance to the butter-making 
industry. The properties of galactase, like those of any other 
enzyme, are destroyed by heating to or above a temperature of 
about 175° F. 
The organized ferments are by far the most important to the 
dairy industry. It should be understood in this connection 
that the organized ferments may produce unorganized ferments, 
or enzymes, as products, but these produced enzymes do not 
exist in milk, like galactase, when it is first drawn from the cow. 
The organized ferments of milk consist chiefly of bacteria. 
There are present also some yeasts and molds. 
It is a common impression that bacteria are animals, which 
is incorrect. Bacteria are minute microscopical plants, belong- 
ing to the lowest order of plants in the vegetable kingdom. 
Bacteria differ from the ordinary plants that we see, in that 
they are composed of a single cell containing protoplasm, 
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