CRBAMBRY BUTTER MAKING 61 



that the separator runs at full speed during the separating 

 process. The speed indicator should alwa_\s be applied 

 before turning on the milk and several times during the 

 run. Loose belts, pulleys slipping on the shaft, and low 

 steam pressure will reduce the speed of the separator. 



B. A separator should run as smoothl}- as a top. The 

 slightest trembling will increase the loss of fat in the 

 skim-milk. Trembling of bowl ma}' be caused by any of 

 the following conditions: (i) loose bearings, (2) sepa- 

 rator out of plum, (3) dirty oil or dirty bearings, (4) un- 

 stable foundation, or (5) unbalanced bowl. 



C. The best skimming is not possible with any sepa- 

 rator when the temperature falls below 60° F. A tem- 

 perature of 85" F. is the most satisfactory for ordinary 

 skimming. Under some conditions the cleanest skimming 

 is obtained at temperatures above 100° F. The reason 

 milk separates better at the higher temperatures is that 

 the viscosity is reduced. 



D. Sudden heating tends to increase the loss of fat 

 in skim-milk in ordinary skimming. The reason for this 

 is that the fat heats more slowly than the milk serum 

 which diminishes the difference between their densities. 

 When, for example, milk is suddenly heated from near 

 the freezing temperature to 85" F. by applying live steam, 

 the loss of fat in the skim-milk may be four times as 

 great as it is under favorable conditions. If, instead of 

 suddenly heating the milk to 85", it is heated to 160° or 

 above, then no extra loss of fat occurs. Hence the ad- 

 vantage of separating milk at pasteurizing temperature 

 during the winter. 



E. Unduly crowding a separator increases the loss 

 ■of fat in the skim-milk. On the other hand, a marked 

 underfeeding is apt to lead to the same result. 



