146 THE CHEMISTRY OF THE FAITJ. 



The large globules diminish in number as the time from 

 calving increases. As the fat globules have a lower 

 specific gravity than the serum in which they float, they 

 tend to rise to the surface, where they form a layer of 

 cream. The largest globules are the first to rise; the 

 smallest never rise at all. Milk containing an abundance 

 of large globules is best for butter-making, as the cream 

 then quickly and perfectly rises ; but milk with small 

 globules is probably best for cheese-making, as a more 

 even distribution of fat throughout the curd is then 

 obtained. 



Milk, when it leaves the cow, will have a temperature 

 of about 90 Fahr. ; when set for cream it should be 

 cooled as quickly as possible, as changes in composition 

 would rapidly occur at a high temperature. Milk is 

 usually set for cream in shallow vessels, the depth of 

 milk being perhaps three inches ; in these vessels the milk 

 stands for thirty-six to forty-eight hours till the cream 

 has separated. Under these conditions a large surface 

 is exposed, the milk receives a large number of bacteria 

 and moulds from the air, and a maximum amount of change 

 takes place ; the result is a decomposition of a part of 

 the albuminoids and fats, the production of lactic acid, 

 and the partial curdling of the milk. The cream obtained 

 in this way is contaminated with curd, and contains 

 various strongly-flavoured products of decomposition, 

 which deteriorate the quality of the butter. 



On Swartz's plan the milk is placed in metal pails, 

 16 inches deep, and surrounded by ice. The cream rises 

 quickly, and can all be obtained in twelve to twenty-four 

 hours from the time of setting. Cream thus prepared is 

 perfectly sweet, and free from curd, the low temperature 



