30 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



Bacilli of the coli-aerogenous group may produce an 

 unclean, even nauseating, taste with a stable or manure- 

 like odor, while the lactic acid bacteria give to milk a 

 sour odor and taste. Specific organisms have been iden- 

 tified which produce bitter, soapy, oily, and burnt tastes 

 and a stable-like odor and taste. Other bacteria produce 

 a rancid odor and taste, and some produce an unclean 

 odor and taste. While some of the peptonizing bacteria 

 (udder cocci) are normal inhabitants of the udder, the 

 other bacteria usually enter the milk after it is drawn 

 from the cow. Sometimes, however, bacteria which are 

 the cause of abnormal odors and tastes become estab- 

 lished in the udder. Odors and tastes of bacterial origin 

 are often not apparent until a certain period after the 

 milk has been taken from the udder and usually become 

 more pronounced as the milk increases in age. Milk 

 acquires a cooked taste when heated above 68 to 71 C. 

 (155 to 160 F.) Heating in open vessels has a more 

 pronounced effect on the taste than heating in closed 

 vessels or bottles. 



The senses of smell and taste tire very quickly and 

 cannot be depended upon to judge many samples of 

 milk. Odors and tastes are more apparent when the 

 milk is warm. 



Specific Gravity. As would naturally be expected 

 from the statements made in regard to the variation in 

 the composition of milk, the specific gravity or density 

 of different samples of milk varies considerable. The 

 range of variation is greater for individual milk than 

 for market milk. The specific gravity of the milk of 

 individual cows will range from 1.027 to 1.040, while 

 that of market milk will fluctuate between 1.028 and 

 1.034, with an average of 1.032, at the standard tempera- 



