134 CHEESE AND CHEESE-MAKING 



present in milk in the form of tiny globules ; 

 these globules are much lighter than the other 

 portion of the milk, hence when the milk is at 

 rest they rise to the surface just as a cork rises 

 to the surface of a volume of water at the bottom 

 of which it has been placed. The reason why 

 the fat rises better in warm milk placed in a 

 cold apartment is that the fat feels the change 

 of temperature less rapidly than the rest of the 

 milk, inasmuch as it is a non-conductor of heat. 

 This being so, the difference in the density or 

 specific gravity of the fat and the liquid portion 

 of the milk is greater, and the fat is relatively 

 lighter than it would otherwise be where there 

 is no difference in the temperatures. In hot 

 weather cream rises with far greater rapidity 

 than in cold ; milk rapidly becomes acid, both 

 cream and milk thicken or coagulate, and for 

 this reason the smaller globules of fat which are 

 at the bottom of a milk-setting vessel are not 

 able to rise at all they are impeded, as it were, 

 by the coagulation of the casein, hence a pro- 

 portion of the butter-fat is lost to the churn. 

 When, however, cream is raised upon a shallow 

 vessel, it forms a thin layer on the surface and is 



