400 MANUAL OF MILK PRODUCTS 



and this speed should be uniformly maintained. If the speed 

 is lowered, a larger amount of cream will result, but with a 

 lower percentage of fat. If the speed is above that specified 

 for the machine, it will give a smaller amount of cream with a 

 richer test. The rate of inflow is controlled by the float be- 

 tween the supply tank and the separator, and if a constant 

 supply of milk is kept in the tank, little attention need be 

 paid to this factor. The percentage of fat in the whole milk 

 has a decided effect on the richness of the cream. The richer 

 the milk, the higher will be the percentage of fat in the cream, 

 while the thinner the milk, the lower will be the fat test of the 

 cream. This may account for sudden drops in the fat test 

 when new milch cows are added to the herd. If the amount 

 of cream separated at one operation is small, the percentage of 

 fat it contains may be materially affected by the amount of 

 skimmed milk or water used in flushing the separator. If the 

 amount of cream is fairly large, the flushing material will have 

 little effect on the test of the cream. The purpose of the cream 

 screw in the separator is to enable the operator to control the 

 richness of the cream, and this can be done within rather wide 

 limits. When once adjusted, however, it should not be changed 

 without good reason. Changes in the cream screw do not 

 account for the daily fluctuations in the ' percentage of fat in 

 hand-separated cream. These variations are usually due to 

 the variations in the other factors mentioned. It is the com- 

 mon impression that the kind of feed eaten by the cows affects 

 the percentage of fat in the milk, but it has been thoroughly 

 shown by numerous experiments that the percentage of fat in 

 the milk cannot be permanently affected by the nature of the 

 ration. Sudden changes may occur due to radical changes in 

 the feed, but the composition of the milk very quickly goes 

 back to normal. The percentage of fat in the milk is primarily 

 dependent on the breed and the individual cow. 



For the best results, cream with a medium percentage of fat 



