DIVISION IV. 

 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



CHAPTER I.* 

 THE RELATION OF MICROORGANISMS TO MILK. 



IMPORTANCE OF MILK AS A FOOD. 



Fresh normal milk is one of the most important of human foods. 

 It has a pleasant taste and aroma and is generally liked as a food or drink; 

 but unless properly cared for will not long remain in its normal condition. 

 No article of human diet is more susceptible to undesirable changes, due 

 to the delicate nature of the milk itself and to the conditions naturally 

 surrounding its production and handling. The injurious changes which 

 commonly occur in milk are of two kinds. 



ABSORBED TAINTS AND ODORS. 



Milk is very quickly affected by odors of any sort. The foreign 

 odor may be absorbed before the milk leaves the udder if the cow has 

 eaten strong feeds, such as cabbage, onions, etc., or it may be absorbed 

 after the milk is drawn from the cow. If milk is exposed to any 

 strong odor, such as silage or foul air, resulting from lack of venti- 

 lation in the stable at milking time, these odors will be taken 

 up by the milk with surprising rapidity. If placed in an ice chest 

 with fresh strawberries or pineapple, or foods like cabbage or turnips, 

 the milk will very quickly absorb the odor of these foods. The absorp- 

 tion of any foreign odor gives to milk a decidedly disagreeable taste. 

 This is true even when the odor which is absorbed is pleasant in itself 

 as is the case of strawberries or pineapples. When the "off" flavors are 



* Prepared by W. A. Stocking with the exception of the paragraphs treating the acid- 

 forming bacteria, prepared by E. G. Hastings. 



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