THE PASTEURIZATION OF MILK 



does not become condensed upon any unclean sur- 

 face, such as the ceiling or a metal covering over 

 the cooler, and from thence fall back into the milk. 

 If this occurs, very serious contamination may 

 result. 



Open pipe coolers should not be made very long 

 in relation to their height. It can be seen that 

 the water flowing through long pipes will become 

 warmed on the inner surface of the tubes, while 

 the central more rapidly flowing core may still be 

 cool. More effective cooling is obtained where this 

 milk flow is broken up by frequent turns as the 

 water is returned from one pipe to another. 



Second: The cooling may be accomplished in 

 the same apparatus in which the milk is heated 

 and held. This can be done when the tank sys- 

 tem of pasteurization is employed, as illustrated in 

 Figs. 12, 13, 14, 14-B, 15, 16. When cooling is so 

 carried on, the cold water or brine takes the place 

 of the hot water in the pipes, by means of which 

 the heating was originally done. It is found in 

 practice that when the same coil is used for the 

 brine as well as for the hot water, there is dan- 

 ger that careless workmen may allow the brine and 

 the water to become mixed. There is therefore a 

 160 



