162 



SEPARATION OF CREAM 



in determining the efficiency of the subsequent separation. For 

 instance, the milk in most horizontal pasteurizers is, even at low 

 speed, exposed to considerable agitation. 



If the milk is suddenly heated from a low temperature to 

 about 80 or 90 F. and then skimmed, the heating does not 

 facilitate the skimming process very much. It is essential that 

 the milk be exposed to this temperature for a considerable time. 

 The fat-globules do not warm as rapidly as the milk serum. This 

 diminishes the difference between the specific gravity of the two 

 substances, consequently completeness of separation becomes 

 more difficult. If milk is heated to a high temperature, say, for 

 instance, 170 F., the separation will be sufficiently complete 

 without exposing the milk for any length of time to that temper- 

 ature. 



Machines are now made, and are on the market, which will 

 bring the milk into such a condition that the fat-globules cannot 

 be separated from it. The process is called " homogenization." 

 It consists of bringing the milk under certain pressure, and then 

 forcing it out through a special valve. This relief, through this 

 special valve, breaks up the existing fat-globules into very 

 minute ones, which cannot be separated from the milk by 

 gravity mehtods, and which it is impossible to separate com- 

 pletely by centrifugal methods. Homogenization of milk is 



