33 



Cream. 



Cream may be defined as that portion of the milk in which has been 

 gathered the hirgest proportion of fat. It is composed of the same sub- 

 stances found in the milk, but these substances do not exist in the same 

 relative proportions. Cream separates naturally from the milk because 

 of the difterence in specific gravity between the globules of fat and the 

 remainder of the milk (milk serum). If milk is allowed to remain at 

 rest in a vessel the fat globules, being lighter than the other ingredients, 

 rise to the surface of the liquid. In so rising they carry with them a 

 portion of the other materials of the milk, and the mixture is called 

 cream. While the composition of the cream varies, especially in its fat 

 content, depending upon the method of separation, the following figures 

 give an idea of an average samjjle of Cooley cream : — 



Cream. Per Cent. 



Water, 72.9 



Fat, 18.0 



Albuminoids, 3.90 



Milk sugar, 4..'iO 



Ash, 69 



Methods of Separating Cream. 



The three methods of separating cream from the milk may be defined 

 as the shallow pan, deep setting and separator systems. 



The quantity of cream for consumption is not seriously affected by 

 either of these methods of separation, so that relative economy depends 

 upon the completeness and cost of separation. 



In the separation of cream by force of gravity there is a great loss of 

 fat, and a longer time required, than when the centrifugal process is 

 employed. According to Wing, the conditions of the milk that atFect the 

 creaming by the gravity process are first, the size of the fat globules ; 

 second, the amount of solids not fat in the milk ; third, the character of 

 the solids not fat ; and fourth, the temperature of the milk. 



The larger the fat globules the more rapidly they separate from the 

 milk The size of the globules is dependent upon the breed and in- 

 dividuality of the cow, and uidou the period of lactation. The amount 

 of solids not fat affects the rising of the cream, because of the difterence 

 in specific gravity between the fat and the other ingredients. Solids 

 not fat are heavier than water, and hence the larger the amount of solids 

 not fat the more rapid one would expect the separation. The favorable 

 eftects of the solids not fat are, as a rule, however, moi'e than oftset by 

 the character of the solids. The solids not fat are the casein, albumin, 

 sugar and ash, and these in the order enumerated increase the viscosity 

 of the milk. This increase in viscosity retards the separation of the fat 

 to a greater degree than the increase in specific gravity tends to aid it. 

 This increase in solids and viscosity takes jjlacc as tlie size of tiie fat 



