514 



MILK 



is heated to a relatively high temperature for a short period. 

 This method is practised in Denmark, .where milk is heated to 

 85 C. for about half a minute. At this temperature there is a 

 great reduction in the number of bacteria. The system has been 

 successful in Denmark, especially as an aid in controlling bovine 

 tuberculosis. Skimmed milk from creameries and whey from 

 cheese factories are pasteurized by this method, and Bang states 

 that a temperature of 85 C. always destroys tubercle bacilli. 



In some types of pasteurizers the milk is either forced up or 

 flows by gravity over or between heated surfaces. These types 

 are illustrated in Figs. 200-206. 



At* 



Fig. 200. A simple pasteurizer through which milk flows by gravity. 

 (S. H. Ayers in Circular 184, Bureau of Animal Industry, U. S. Dept. of 

 Agriculture.) 



The tubular type of continuous pasteurizers consists of a 

 series of pipes through which the milk flows. These pipes are 

 contained in larger pipes filled with hot water. This type is 

 shown in Fig. 204. The same system is used for cooling the milk 

 when the larger pipes contain the cooling mixture. 



Regenerative pasteurizers are those in which the water is 

 preheated, by being used for cooling the hot milk. This prin- 

 ciple is designed to save heat units (Figs. 205 and 206). 



Harding and Rogers, after studying at different temperatures 

 the efficiency of a continuous pasteurizer of the Danish type, 



