CHAPTER V 

 FERMENTS IN MILK 



Definition. The changes which milk undergoes when 

 allowed to stand at a suitable temperature are commonly called 

 fermentations, and the agencies which bring about these changes 

 are called ferments. At one time the ferments were classified 

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

 and molds), and enzymes 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 enzymes which these micro-organisms produce. However, 

 the enzymes themselves may, from a dairy standpoint, be classi- 

 fied as follows: 



(i) The pre-existing enzymes of milk, or those which are 

 formed during milk secretion and consequently are in the milk 

 when it is drawn from the cow. The first of these was dis- 

 covered 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 peroxi- 

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

 made by Russell and Babcock, that the inherent enzymes of 

 milk, which are digesting ferments, are essential to and play an 

 important role in the ripening of the Cheddar type of cheese. 

 They find that it is impossible to produce a typical, normal 

 Cheddar cheese from thoroughly pasteurized milk. According 

 to S torch, the peroxidase has the power of decomposing hydrogen 

 peroxide and setting free " active " oxygen. As this ferment is 

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



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