140 



BITTER-MAKING. 



effect the different degrees of agitation of milk has upon the 

 efficiency of separation : 



In the above experiments the diameter of the agitator in 

 the Pasteurizer was 14 inches. The speed at the periphery, 

 at 250 revolutions per minute, was 5 feet per second. 



It will be seen from the above table that the higher the 

 speed of the agitator, the greater the difficulty in getting a 

 complete separation. Besides the speed of the agitator in 

 the heating apparatus, undoubtedly the shape of the Pas- 

 teurizer is a factor in determining the efficiency of the 

 subsequent separation. For instance, the milk in^most hori- 

 zontal Pasteurizers is, even at low speed, exposed to con- 

 siderable 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 should 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 complete- 

 ness of separation becomes more difficult. If milk is heated 

 to a high temperature, say, for instance, 170 F., then the 

 separation will be sufficiently complete without exposing the 

 milk for any length of time to that temperature. 



