226 MANUAL OF MILK PRODUCTS 



factors will affect the creaming process. The conditions which 

 most commonly affect the creaming process are : the size 

 of the fat globules, the percentage of solids not fat, and 

 the viscosity of the serum. The larger the fat globules, the 

 more easily they rise to the surface, because of the greater mass 

 in proportion to the surface. For this reason, the milk from 

 certain breeds, as the Jersey and Guernsey, creams more easily 

 than that of others, as the Ayrshire and Holsteins. Since the 

 fat globules decrease in size as the lactation period advances, 

 the milk from new milch cows will cream more easily than that 

 of cows far advanced in the period of lactation. 



Since the solids not fat are all heavier than water, their in- 

 crease will increase the specific gravity of the milk-serum and 

 increase the difference in specific gravity of the fat globules 

 and the serum, thus making it easier for the cream to rise. 

 However, an increase in solids increases the viscosity of the 

 serum and retards the rising of the cream. The presence of 

 fibrin in the milk may also interfere with the creaming process. 

 Regarding the influence of fibrin upon the creaming process, 

 Babcock * says : 



"As the clots of fibrin are heavier than the milk-serum and 

 become attached not only to the fat globules, but to other solid 

 particles in the milk, often to the sides of the vessel in which 

 the milk is set, it is evident that even the small amount of fibrin 

 in milk may be a great hindrance to thorough creaming. If 

 this is true, the most efficient creaming should be obtained when 

 the conditions are such as to oppose the coagulation of fibrin. 

 This is believed to be true in all gravity systems of creaming, 

 at least all improvements which have been made in these 

 systems have been in this direction. The centrifugal separator 

 accomplishes the same end by making the effective difference 

 between the weight of fat and the fibrin clots so great that the 

 disadvantage is overcome, the fibrin being to a considerable 



i Wis, Report, 1893, p. 145. 



