88 VARIATION OF FAT IN MILK AND CREAM 



the amount of cream to 7 pounds. The effect of these variations 

 of speed on the richness of the cream are shown in Fig. 16. 



Fig. 1 6 demonstrates conclusively that high speed yields rich 

 cream and low speed yields thin cream. At normal speed, the 

 cream tested 44 per cent fat, at low speed 1 1 per cent fat, and at 

 high speed 63 per cent fat. The very low test of cream from a 

 low speed separation is, in part, due to the fact that a large 

 amount of fat (about one-half of the fat of the milk) is lost in the 

 skim-milk. 



How to Run the Separator at the Right Speed. The proper 

 speed is indicated on the crank of the machine. It varies from 

 about 40 to 60 turns of the crank per minute, according to the 

 make of the separator. If a separator is to yield cream of uniform 

 richness, it must be given the same speed at each skimming. 

 This is possible only if the operator times himself frequently, 

 counting the revolutions of the crank with watch in hand, or by 

 the use of a patent speed indicator. The absence of this pre- 

 caution renders the work unreliable. The general tendency on 

 the part of the operator is to overestimate the amount of work he 

 puts into the machine; the machine is run at too low a speed. 

 Even the same operator may vary the speed very considerably 

 at different times, depending on his frame of mind and physical 

 condition. Again, where different persons operate the machine, 

 there can be but little uniformity of speed, unless each person 

 makes an effort frequently to count the crank revolutions by the 

 watch. The use of a gasoline engine or some constant power 

 will tend to give a more uniform cream than when the machine is 

 operated by hand. 



5. Effect of Temperature on Richness of Cream. The higher 

 the temperature the thinner the cream. The temperature 

 influences the rate of inflow. The warmer the milk the more 

 rapidly will it run from the supply tank into the bowl. Since 

 the capacity of the skim-milk outlet is fixed, the increased inflow 

 of the milk is discharged through the cream outlet, producing a 

 thinner cream. Experimental results showed that when the 

 separator was so adjusted as to yield 15 pounds of cream and 

 85 pounds of skim-milk from every 100 pounds of milk separated 



