VARIATION OF FAT IN CREAM 83 



by the cream screw. The centrifugal separator has two main 

 outlets, namely, the skim-milk outlet located near the periphery 

 or outer wall of the bowl, and the cream outlet, located near the 

 center of the bowl. 



When the milk enters the revolving bowl it is separated into 

 two layers, the skim-milk and the cream. The skim-milk, being 

 heaviest, is thrown against the walls of the bowl where it escapes 

 through the skim-milk outlet. The cream is drawn toward the 

 center of the bowl, where it rises and is discharged through the 

 cream screw or cream outlet. The cream screw is a small 

 threaded bolt with a very minute opening. This bolt can be 

 turned so as to move the opening nearer or farther from the cen- 

 ter of the bowl. When turned toward the center it delivers 

 richer cream, because a smaller proportion of the milk is taken 

 as cream. When turned out from the center it delivers thinner 

 cream, because a larger proportion of the milk is taken as cream. 



2. Effect of Richness of Milk on Richness of Cream. The 

 richer the milk, the richer will be the cream. With the cream 

 screw set to deliver a certain and definite richness of cream and 

 all other conditions normal, the separator will deliver a definite 

 ratio of skim -milk and cream. This ratio varies according to the 

 way the cream screw is set. Under average conditions it may be 

 about 85 to 15; that is, for each 100 pounds of milk separated 

 the separator delivers 85 pounds of skim-milk and 15 pounds of 

 cream. If all conditions are the same, this ratio of skim-milk 

 to cream remains constant. Changes in the richness of the milk 

 cannot alter the proportion of skim-milk to cream delivered. 

 No matter how rich or how poor the milk, each 100 pounds 

 of milk will yield 85 pounds of skim-milk and 15 pounds of 

 cream. 



But because practically all of the fat goes into the cream, the 

 cream will contain more fat from the separation of rich milk 

 than from that of thin milk. This fact is graphically illustrated 

 in Fig. 14. 



The illustration (Fig. 14) conclusively shows that, all other 

 conditions being the same, 3 per cent milk produces 20 per cent 

 cream, 4.5 per cent milk produces 30 per cent cream, and 6 per 



