Cream vSeparation 1875 



there are ninety pounds of skimmed milk (100 pounds — 10 pounds = 90 

 pounds). The ratio of the cream (10 pounds) to the skimmed milk (90 

 pounds) is one to nine. If cream having a lower percentage of fat is desired, 

 this ratio will be less. Cream with a lower percentage of fat is often 

 used on the table and for making ice cream. In separating cream for these 

 purposes the ratio of cream to skimmed milk should be about one to four, 

 to five, or to six, depending on the percentage of fat in the whole milk. It 

 is readily seen that a comparison of the quantities of cream and skimmed 

 milk obtained in separation gives a close approximation of the percentage 

 of fat in the cream. These ratios are shown in Figure 82, which also gives 

 the results of temperature study of one separator. This topic is discussed 

 later in the lesson. The figure makes clear the fact that if cream with a 

 high percentage of fat has been separated, no more fat has been obtained 

 from a given amount of whole milk than if the cream has a low fat con- 

 tent, for the weight of the cream is less. 



If a well-made centrifugal separator is operated properly, it will separate 

 cream containing as high as forty-five to fifty per cent of fat, and there will 

 be only the normal loss of fat in the skimmed milk. Usually it is not de- 

 sirable that cream should contain more than forty to forty-five per cent of 

 fat, for very rich cream is wasted by sticking to cans, dippers, and other 

 utensils, and it is difficult to obtain a representative sample of it for testing. 



The fat content of cream cannot be controlled to a definite percentage by 

 the regulation of the cream screw or the skimmed milk screw, and the per- 

 centage of fat in cream will not remain constant even when these screws are 

 not changed. There are certain factors that affect the percentage of fat 

 in cream to a greater or less degree as it is being separated.^ The effect of 

 these factors on the percentage of fat in skimmed milk is not so noticeable 

 as their effect on the percentage of fat in cream. 



Factors that affect the percentage of fat in cream and in skimmed milk separated 



by a hand centrifugal separator 



The temperature of the whole milk. — The temperature of milk that is being 

 separated should be such that the milk will flow easily, in order to facilitate 

 rapid and thorough separation of the cream and the skimmed milk. The 

 temperature does not need to be as high as the body temperature of a cow, 

 which is normally about 101.4° F.; however, if the separation is done on 

 the farm, milk should be separated as soon as possible after it has been 

 milked, especially in the winter. In creameries and in other places where 

 milk is separated after it has cooled, the temperature of the milk should 

 be raised to 85° to 90" F. before it is separated. The temperature of the 



' A more complete study of the conditions that affect cream separation is recorded in Bulletin 360 of 

 the Cornell University Agricultural Experiment Station. This bulletin will be ready for distribution July 

 IS, 1915. 



