CHAPTEE V 



PRESERVATION OF MILK 



It is impossible to produce milk that does not contain a 

 greater or less number of bacteria, since some of the sources 

 of contamination are of such a nature that they cannot be 

 wholly avoided. A large part of the bacteria that gain en- 

 trance to the milk find it a favorable nutrient medium, and 

 products are produced in it as a result of their growth, so 

 that it is rendered more or less unpalatable, or even danger- 

 ous as human food. 



The period during which milk is fit for use is usually to 

 be measured by hours rather than by days. When the milk 

 is consumed at or near the place of production, the question 

 of preservation is of no great economic importance. With 

 the growth of the modern city, however, the zone from which 

 the milk must be drawn has widened until, in many cases, it 

 is transported for hundreds of miles and does not reach the 

 consumer for twenty-four to forty-eight hours after with- 

 drawal from the animal. It is thus exceedingly desirable 

 that, so far as possible, bacterial life be excluded from milk 

 by the exercise of the most rigid but practicable methods 

 while in the hands of the producer. It is also quite as 

 necessary that the milk while in transit be kept under such 

 conditions as will check bacterial growth. 



While the partial exclusion of bacteria will enhance the 

 keeping quality of the product, milk preservation is more par- 

 ticularly limited to those methods by which the organisms 



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