CHAPTER IV. 



FERJIEXTS IX 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 galadase. 

 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 M'ere 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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