Preservation of Milk. 



131 



FIG. 27. Potts pasteurizer. 



and which conforms to the necessary biological conditions. 

 This apparatus has a central milk chamber that is sur- 

 rounded with an 

 outer shell con- 

 taining hot water. 

 The whole ma- 

 chine revolves on 

 a horizontal axis, 

 and the cream or 

 milk is thus thor- 

 ough^ agitated 

 during the heating 

 process. 



Coolers, A speedy cooling of the heated product is 

 essential to success in pasteurizing. Some of the machines 

 have been devised for a combination purpose, being used 

 for the heating and subsequent cooling of the milk. This 

 is an evident advantage in some ways, as it lessens the 

 amount of apparatus necessary, also the work involved in 

 cleaning the same, but at the same time the problems of 

 quick heating and cooling involve somewhat different 

 principles, so that for the most economical manipulation of 

 the product, separate pieces of apparatus are advisable 

 where the business warrants such expense. 



The simplest method of treatment in cooling is to draw 

 off the milk in shot-gun cans and place these first in water, 

 then in ice-water. 



To cool milk most economically, two coolers should be 

 provided. With one of these, cold water can be used, and 

 with this the temperature can be reduced to nearly that 

 of the water in a short time. In order, however, to 

 lower the temperature below a point where spore germi- 

 nation will readily occur, milk should be chilled by the 



