CONTROL OF THE MILK SUPPLY 



235 



a smaller number of spore-bearing germs than that which contains a 

 high percentage of acid. 



Lastly, while the heating process is, of course, the essential feature 

 of efficient pasteurisation, it must not be forgotten that rapid and 

 thorough cooling is almost equally important. As we have seen, 

 pasteurisation differs from complete sterilisation in that it leaves 

 behind a certain number of microbes or their spores. Cooling 

 inhibits the germination and growth of this organismal residue. If 

 after the heating process the milk is cooled and kept in a refrigerator, 

 it will probably keep sweet from three to six days, and may do so 

 for three weeks. 



Results of Pasteurisation. Before leaving this subject, we may 

 glance for a moment at the bacterial results of pasteurisation and 

 sterilisation. The two chief of these are the enhanced keeping 

 quality and the removal of disease-producing germs. The former is 

 due in part to the latter, and also to the removal of the lactic acid 

 and other fermentative bacteria. As a general rule, these bacteria 

 do not produce spores, and hence they are easily annihilated by 

 pasteurisation. True, a number of indifferent bacteria are untouched, 

 and also some of the peptonising species. The cooling itself con- 

 tributes to the increased keeping power of the milk, especially in 

 transit to the consumer. 



Pasteurised milks have the following three economical and com- 

 mercial advantages over sterilised milks, namely (a) they are more 

 digestible, (&) the flavour is not altered, and (c) the fat and lact- 

 albumen are unchanged. Professor Hunter Stewart, of Edinburgh, 

 compiled from a number of experiments the following instructive 

 and comprehensive table: 



