DAIRYING 



Another possible cause of the cream rising better at a low 

 than at a high temperature is that the surface tension is increased 

 at lower temperatures, and the fat globules in milk unite more 

 rapidly at low than at high temperatures, forming larger lumps 

 of fat, that rise to the surface easier than smaller ones. 



Up to the. present time, no method has been devised that will 

 recover all the fat of milk in the cream; losses occur during each 

 handling of the milk, first from waste by milk sticking to the 

 pails, cans or machines, and second, some fat is always left in 

 the skim milk. The amount of butter fat lost in these two ways 

 may be very small or it may be a large percentage of the fat 

 in the whole milk. The extent to which the milk fat is recovered 

 in the cream will depend largely on the efficiency of the method 

 of cream separation used, and the ability and carefulness of the 

 person doing the work. 



In the early days little was known about milk except that 

 cream will rise when it is allowed to stand quietly for a few 

 hours. This is the simplest division of milk into its component 

 parts, i. e., separating the cream from the skim milk or the fatty 

 portion from the serum. We know at the present time that the 

 solids in the milk have a very complex composition, but without 

 going deeply into the subject we will consider briefly the relation 

 which the milk constituents have to cream separation. 



CAUSE OF CREAM SEPARATION 



214. When milk is divided into cream and skim milk, the 

 greater portion of the milk serum is left in the skim milk. A cer- 

 tain amount of it gets into the cream, but this cream-serum is of 

 about the same composition as the milk serum. Skim milk con- 

 taining no fat is therefore a good illustration of what is known as 

 milk serum. It is heavier than water, having a specific gravity 

 of 1.04; and in normal milk the butter fat, which has a specific 

 gravity of .9, is suspended in the milk serum in the form of 

 microscopic globules. 



