152 SEPARATION OF CREAM 



great as that of water, so that in order to maintain the same rela- 

 tive difference in their specific gravities when the temperature is 

 falling, the milk serum must cool nearly three times as quickly 

 as the fat. In other words, when the milk serum has cooled from 

 90 to 40, or 50 F., the fat-globules should have lost less than 

 17, and should still have a temperature of over 70 F., a differ- 

 ence between the temperature of milk serum and fat of more 

 than 33. Such a condition is manifestly impossible, but 

 a less difference than this would cause the fat to become 

 relatively heavier than at first, and would operate against the 

 creaming." 



A low temperature increases the viscosity of the milk, and 

 consequently it would seem that the resistant force of the fat- 

 globules in their upward passage through the milk serum would 

 be increased, and thus retard the creaming. Babcock maintains 

 that fibrin is partially precipitated when milk is allowed to stand 

 at a medium high temperature. The fibrin, when precipitated, 

 forms a fine network of threads permeating the milk in all direc- 

 tions, similar to the network of fibrin in coagulated blood. It is 

 possible to conceive that such a network would interfere with the 

 rising of the fat-globules, at comparatively high temperatures. 

 The reason that fat-globules will rise more quickly and more 

 completely in the deep-setting system than in the shallow-pan 

 system, might be explained on this fibrin theory were it not for the 

 fact that experiments conducted at the Cornell Experiment 

 Station show that the setting and cooling of milk may be delayed 

 long enough for this fibrin to form, without any effect upon the 

 separation when set and cooled. 



Probable Explanation. There are two factors which, taken 

 in conjunction with each other, seem to offer a reasonable 

 explanation of the efficiency of the deep-setting system. 



The first of these is that cooling the milk to, and holding 

 it at, a low temperature keeps the milk serum in a much better 

 physical condition. It may not be so fluid as it would be at a 

 higher temperature, but there is a minimum formation of fine 

 masses or particles of curdy matter that would either imprison 

 some of the fat or offer obstruction to the fat-globules, and 



