CHAP1ER V 

 FERMENTS IN MILK 



Definition. — The changes which milk unrlergoes when 

 allowed to stand at a suitable temperature are commonly called 

 fermentations, and the agencies which bring al)out these changes 

 are called ferments. At one time the ferments were classified 

 under two heads, viz., organized ferments (bacteria, yeasts 

 and molds), and enz\nres or unorganized ferments, such as those 

 found in rennet and other fluids in the digestive tracts of animals. 

 This distinction is no longer made, since bacteriologists and 

 physiological chemists have reached the conclusion that the 

 fermentative changes, due to the action of germ life, are caused 

 by enzjaiies which these micro-organisms produce. Howe^'er, 

 the enz\iTies themselves may, from a dairy standpoint, be classi- 

 fied as follows: 



(i) The pre-existing enz\Tnes of milk, or those which are 

 formefl during milk secretion and consequenth' are in the milk 

 when it is rlrawn from the cow. The first of these was ch's- 

 covercd by Babcock and Russell of the Wisconsin Station, in 

 1889, and was named galactase by the discoverers. It is a 

 tryptic ferment. Since then others, such as catalase and pero.xi- 

 dase, have been discovered. It would seem, from investigations 

 made by Russell and Baljcock, that the inherent enzxnnes of 

 milk, which are digesting termcnls, are essential to an:l ph\ an 

 important role in the rijjening of tin' Cheddar type of cheese. 

 They find that it is iinpossible to i)roduce a, typical, nornral 

 Cheddar cheese from thoroughly pasteurized milk. According 

 to Storch, the ])eroxidas(.' has the ])owi'r of decomposing hydrogen 

 pero.xide and setting Iree " acti\'e " o.xvgen. As this ferment is 

 not destroyed until milk or cream is heated to a high temperature, 



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