132 Dairy Bacteriology. 



aid of ice. This may be applied in the same cooler that is 

 used for running cold water, by supplying ice-water for the 

 latter part of the cooling process. To use ice economically, 

 the ice itself should be applied as closely as possible to the 

 milk to be cooled, for the larger part of the chilling value 

 of ice comes from the melting of the same. To convert a 

 pound of ice at 32 F. into a pound of water at the same 

 temperature, if we disregard radiation, would require as 

 much heat as would suffice to raise 142 pounds of water 

 one degree F., or one pound of water 142 F. The ab- 

 sorptive capacity of milk for heat (specific heat) is not quite 

 the same as it is with water, being .847 for milk in com- 

 parison with 1.0 for water. 1 Hot milk would therefore 

 require somewhat less ice to cool it than would be required 

 by an equal volume of water at the same temperature. 



In the mere melting of a pound of ice, if expended on 

 cooling heated milk, the temperature of pasteurized milk 

 would be reduced to a keeping temperature. To take ad- 

 vantage of this, the ice should be brought in close contact 

 with the milk, rather than to utilize the specific heat in 

 cooling water which is later applied to the milk. If broken 

 ice is used directly, it is utilized most economically if the 

 milk surrounds it, as in this way the ice does not absorb 

 heat from the outside. 



Bacterial efficiency of pasteurizing; apparatus. The bac- 

 terial content of pasteurized milk and cream will depend 

 somewhat on the number of organisms originally present 

 in the same. Naturally, if mixed milk brought to a cream- 

 ery is pasteurized, the number of organisms remaining 

 after treatment would be greater than if the raw material 

 was fresh and produced on a single farm. 



An examination of milk and cream pasteurized on a com- 



1 Fleischmann, Landw. Versuchsstat., 17: 251. 



