126 BUTTER-MAKING. 
impossible that under any circumstances there can be more 
than a small fraction of a degree of difference between the 
temperature of the fat and that of the milk serum. More- 
over, with the limits of temperature practical for a creamery, 
(90° to 40° F.), the coefficient of expansion of butter-fat is 
more than three times as great as that of water, so that in 
order to maintain the same relative 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-glabules should have lost less than 17°, and should 
still have a temperature of over 70° F., a difference between 
the temperature of milk serum and fat of more than 33°. Such 
a condition is manifestly impossible, but no 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 directions, 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-glob- 
ules, 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.—It is a well known fact in physics 
that most liquids, when present in the form of drops, increase 
