164 Milk and Its Products 



which tends to increase the surface tension or the 

 viscosity will act as a hindrance towards the sepa- 

 ration of the cream. While the viscosity of the milk 

 serum prevents the particles of fat from uniting 

 into a mass, still the particles have considerable free- 

 dom of movement in the milk, and being of a less 

 specific gravity, of course are acted upon with less 

 intensity by any force to which the milk is subjected. 

 If the milk is allowed to remain at rest in a 

 vessel, the force of gravity, acting with different in- 

 tensities upon the globules of fat and the milk serum, 

 will cause the particles of fat to gather together 

 near the surface of the liquid. In so gathering, 

 they carry with them certain of the milk con- 

 stituents, and the layer of fat globules and adher- 

 ing particles we call cream. From time immemo- 

 rial, and until within a very recent date, the 

 force of gravity, acting in the way indicated, has 

 been the only means used for separating cream from 

 milk. Now machines are in use that effect a sepa- 

 ration of the cream from milk by means of centrif- 

 ugal force, and at the present time we have three 

 systems of separating cream ; namely, by gravity 

 acting upon a thin layer of milk in a shallow vessel, 

 known as the Shallow Pan System ; secondly, by 

 gravity acting upon a deeper mass of milk, usually 

 submerged or partially submerged in water, known 

 as the Deep Setting System ; and thirdly, by ma- 

 chines making use of centrifugal force, known as 

 the Centrifugal or Separator System. The quality 

 of the cream for consumption or for purposes of 



