CHAPTER V. 

 MILK FERMENTATIONS AND THEIR TREATMENT. 



56. Classification of milk fermentations. If any 



sample of milk is allowed to stand at any ordinary tem- 

 perature for several days, a profound physical and chemi- 

 cal change inevitably takes place. As a rule the milk will 

 sour. In this process, certain acids are formed at the 

 expense of the milk-sugar. If it is still allowed to stand 

 for some time after it has become thoroughly sour, a 

 series of subsequent changes usually occur. Often it will 

 evolve foul- smelling gases and undergo putrefactive 

 changes. Sometimes, however, other ferment organisms 

 gain the ascendency over the ordinary souring process, 

 in which case the fermentation is said to be abnormal. 

 These peculiar changes are the cause of various taints in 

 milk. They are of great importance because a small 

 quantity of milk tainted in this way is liable to infect a 

 much larger quantity and spoil the same through the 

 rapid development of the obnoxious organism. In some 

 cases, the abnormal condition may not become marked 

 until the milk is made up into some other product as 

 butter or cheese. The difficulties that occur under these 

 conditions will be discussed under their appropriate heads. 

 It is impossible in the present state of our knowledge 

 to classify these fermentations in any other than a most 

 provisional way. While our knowledge of some of them 

 from a bacteriological standpoint is fairly complete, so 

 many, as yet, have been studied only superficially that we 

 are not in a position to classify them as we would other 



chemical changes. 



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