196 MODERN DAIRY PRACTICE. 



be considered the " cleanest of all milk." But this purity 

 of the separator skim-milk is far greater and more impor- 

 tant than he suspected at the time. He gave this opinion 

 because he saw the great advantage arising from the 

 removal of the microscopic impurities of the milk by 

 means of the centrifugal force. It has now further been 

 established that separator skim-milk contains fewer bac- 

 teria than even the milk from which it was prepared. The 

 data given on page 184 give decided evidence on this 

 point. Separator skim-milk will, therefore, keep better than 

 any other not especially prepared milk. It is furthermore 

 more palatable than other skim-milk, since it is purer and 

 may be obtained in almost as fresh condition as new milk.* 

 The separation may take place directly after the milking, 

 and if the skim-milk is cooled immediately after this opera- 

 tion it will keep well. 



Pasteurization of Skim-milk. The keeping quality of 

 the separator skim-milk may be further increased by pas- 

 teurization and subsequent rapid cooling. These opera- 

 tions are especially essential if the milk has become highly 

 infected by bacteria in the stable or during the transporta- 

 tion. As shown by the table given on page 184 not even 

 the separation is sufficient to produce skim-milk poor in 

 bacteria, and it is therefore necessary to adopt further pre- 

 cautions to maintain the keeping quality of the milk, for 

 which purpose pasteurization and cooling are especially 



* Fjord in Tidsskrift for Landokonomi, 1883, says: "As regards 

 the sweetness of the centrifugal skim-milk it may be taken for 

 granted that every housewife will prefer a sweet milk poor in fat for 

 a half-soured, richer milk, no matter if the milk is consumed un- 

 boiled, or if it is to be previously boiled, by which process the sour 

 milk is easily coagulated." 



