180 BUTTER-MAKING. 
and the better the results are. If pasteurization is not prop- 
erly conducted, often the sour milk and cream coagulate and 
get very lumpy. This takes place chiefly when pasteurization 
‘s attempted at a comparatively low temperature, at a slow 
rate of speed of the agitator in the pasteurizer, and when there 
is about from .38% to .4% acidity in the cream or milk. Sour 
thin cream—less than 28% fat—does not pasteurize successfully. 
In case there is any danger of sliminess taking place during 
pasteurization, the heat should be applied as quickly as possible. 
Only a thin layer of cream 
should be exposed to the 
® heating-surface at one time. 
Flashy, quick heat tends to 
prevent this slimy condition. 
The speed of the stirrer should 
be increased, if possible, when 
such cream is being pasteur- 
ized. 
‘4 By greasing the inside of 
Ls ae > the pasteurizer, or the heat- 
Fig. 120.—The Miller pasteurizer. | Ing-surface, a trifle previous 
to pasteurization, the burning- 
on can be prevented in part. The casein that adheres can 
be more easily removed than if no grease were used. 
(3) Thickness of Layer of Condensed Steam.—At first glance 
one might come to the conclusion that the small amount of 
steam which is constantly being condensed upon and adhering 
to the steam side of the heating-surface is not sufficient to 
cause any difference in the efficiency of the pasteurizer. Ex- 
periments conducted by Dr. Storch of the Royal Experiment 
Station, Copenhagen, Denmark, show that this condensed steam 
greatly resists the transmittance of heat. The comparative 
heat conductivity of water and copper is .0016 and .9 respec- 
tively, as found by Dr. Storch. It will thus be seen that copper 
is 600 times as good a conductor of heat as water is. This would 
mean that a quiet layer of water 3 millimeters in thickness 
