Milk and Its Products. 281 



diameter and 15 to 20 inches deep, which are then immersed in 

 ice-cold water. The cream rises quickly and the process will be 

 practically complete in 12 hours. By this process 90 to 95 per 

 cent of the fat can be removed, dependent upon conditions of 

 cooling, manipulation, and the breed of the cow. It has been 

 found that by .this process twice as much fat remains in the skim 

 milk from Holstein cows as in that from Guernseys and Jerseys, 

 owing to the slower rising of the small fat globules in Holstein 

 milk. 



Many explanations of the efficiency of this system have been 

 attempted. Since fat expands and contracts with changes of 

 temperature more rapidly than does water, the effect of cooling 

 upon milk would be to lessen the difference in specific gravity 

 between fat and water ; it would also increase the viscosity of the 

 milk, both conditions working against a rapid rise of the fat 

 globules. Perhaps the most satisfactory explanation is the one 

 given by Doctor Babcock. There exists in milk a substance sim- 

 ilar in character to blood fibrin, which, when formed produced 

 more or less of a network throughout the body of the milk. By 

 rapidly cooling the milk, the formation of fibrin threads is 

 checked. This allows the fat globules a free path of movement, 

 with the resultant rapid formation of the cream layer. The ex- 

 istence of fibrin in milk has been definitely proven. 



Separators. A third plan of separating cream is by subject- 

 ing the milk to extremely rapid horizontal revolution in a cen- 

 trifugal machine. Under this condition the serum, being the 

 constituent of heaviest specific gravity, is thrown to the outer 

 side of the revolving vessel while the fat globules rise into the 

 center of the mass. The milk should be warmed to about 85 F. 

 previous to separating, for the purpose of lowering its viscosity. 

 By providing suitable outlets, the skim milk can be directed into 

 one channel and the cream into another. By adjusting the size 

 of one of these openings, thick or thin cream can be obtained at 

 will. Both the cream and skim milk thus obtained, are, of course, 

 perfectly sweet. The separation of the fat is far more complete 



