PAET III. 



SKIM-MILK. 



BEFORE considering the factors which influence the 

 keeping quality of skim-milk it will be in order to point 

 out that there are different kinds of skim -milk of greatly 

 differing qualities, and in many respects of different antece- 

 dents. These differences are mainly due to the different 

 methods of cream separation by which the milk has been 

 obtained. 



SKIM-MILK FROM GRAVITY CREAMING. 



The skim-milk obtained by the old shallow-setting 

 system is already sour when the cream is skimmed off, and 

 as a rule it remains sour for a sufficiently long time before 

 any other fermentation to all appearances occurs. So 

 long as the lactic acid is not too strong in the skim-milk 

 the lactic-acid bacteria may thrive there; but after a 'time 

 their vital force is gradually weakened by the strong 

 acidity which they themselves have produced, and 'to the 

 same extent others, especially the butyric-acid bacteria, 

 enter into full activity. The latter have up to this point 

 only lived a torpor-like existence, but they now grow into 

 activity; the pleasantly acidulated taste, which is the best 



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