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 

 is attempted at a comparatively low temperature, at a slow 

 rate of speed of the agitator in the pasteurizer, and when there 

 is about from .3% to .4% acidity in the cream or milk. Sour 

 thin cream less than 23% 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. 



By greasing the inside of 

 the pasteurizer, or the heat- 

 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 



FIG. 120. The Miller pasteurizer. 



