PASTEURIZATION. 175 



time and temperature are under control. Various pasteuriz- 

 ing machines are in use, and it is not within the province of 

 this work to recommend any machine. A few words in regard 

 to the principles which affect proper pasteurization will serve 

 a better purpose. 



SELECTION OF PASTEURIZERS. 



Improper pasteurization is worse than none at all. If 

 pasteurization is done at all, it is essential that it be properly 

 accomplished. 



There are two things to be sought when purchasing a pas- 

 teurizer; viz., (1) durability and capacity, and (2) economic 

 efficiency. 



1. Durability and Capacity. The structure of most pas- 

 teurizing machines is simple and substantial. They do not 

 wear out like a complex piece of machinery. It is essential 

 that the machine be strongly made. Heating-walls and other 

 portions should be made heavy enough to be consistent with 

 its use, and of a substance which will conduct heat rapidly. 

 Nearly all the types of pasteurizers are made in different sizes 

 to suit the demands. 



2. Economic Efficiency. Obtaining efficient pasteurization 

 economically is the most important question. It is important 

 in this connection because it depends upon so many conditions 

 which the operator has under control. The degree of con- 

 ductivity of heating-surface during operation, may in one sense 

 include most of the essential factors which affect pasteurization. 

 This in turn depends upon a number of conditions which are as 

 follows : 



(1) Kind of material from which the heating-surface is 

 manufactured. 



(2) Degree of adhesiveness of milk or cream on heating- 

 surface. 



(3) Thickness of layer of condensed steam, on steam side of 

 heating-surface. 



(4) Difference in temperature on each side of heating-surface. 



