114 Dairy Bacteriology. 



112. Coolers. A speedy cooling of the heated pro- 

 duct 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 



FIG. 27. Pott's pasteurizer. 



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 appara- 

 tus are advisable where the business warrants such ex- 

 pense. 



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. One of these can use cold water, and by the 

 aid of good well water, 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 germination will readily occur, milk should be 

 chilled by the aid of ice. This may be applied in the 

 same cooler as is used for running cold water, by sup- 

 plying ice- water for the latter part of the cooling process. 



