280 Agricultural Chemistry. 



Products derived from milk. Cream. The fat of milk exists 

 in globules and is specifically lighter than the aqueous portion of 

 the milk. This makes the globules tend to rise to the surface, 

 where they form a layer of cream. The specific gravity of fat 

 at 15 C. is .930, while the serum in which the globules float has 

 a specific gravity of about 1.036. The globules are of various 

 sizes. They are considerably larger in the milk of the Jersey and 

 Guernsey breeds than in the Ayrshire and Holstein breeds. The 

 Devons and Shorthorns hold an intermediate position. The 

 smaller the globule, the larger is its surface in proportion to its 

 volume, and the greater the resistance to its rise. For this reason 

 Jersey milk creams easier than that from breeds with smaller 

 globules. 



Cream can be separated from milk by gravitation or by sub- 

 stituting for gravity the much greater force produced by raptd 

 rotation. When milk leaves the cow it will have a temperature 

 of about 90 F., and where set for cream should be cooled as 

 quickly as possible. There are two methods in use for the separ- 

 ation of cream by the gravity processes, namely, shallow setting 

 and deep setting. In the former the milk is placed in shallow 

 vessels to a depth of 2 to 4 inches, cooled to about 60 F. and 

 kept at that temperature for 24 or 36 hours. The cream layer 

 is then removed by a shallow spoonlike vessel, or sometimes by 

 running off the milk into another vessel through a hole at the 

 bottom of the creaming pan. Under these conditions of cream- 

 ing a large surface is exposed, the milk may receive a great num- 

 ber of bacteria, and decomposition of a part of the protein and 

 sugar may rapidly take place. The cream obtained in this way 

 is liable to be contaminated with various strongly flavored pro- 

 ducts of decomposition, resulting in a poor quality of butter. 

 The process is not efficient, as only about 80 per cent of the milk 

 fat is removed. 



By the deep-setting system, the milk, while still warm, is 

 placed in cylindrical vessels, usually about 8 to 12 inches in 



