Chapter III 



The Preservation of Milk and its Treat- 

 ment for Direct Consumption 



PRESERVATION 



THE general methods used for the preservation of foods are, 

 constant cooling, short heating, concentration, and the addition 

 of bactericidal substances. All four methods or combinations 

 thereof are applied to milk. 



Cooling is most used because it is the cheapest method and 

 because the milk suffers no chemical change in the process. The 

 principle of the method has been discussed above, and it is well- 

 known that the sooner and the more thoroughly the milk is cooled 

 the better will be the result. Even in cold weather the milk 

 cannot be cooled quickly enough by simply allowing it to give up 

 its heat to the air. It is absolutely necessary to stand the pails 

 in cold water which is frequently changed ; the level of the water 

 must be higher than that of the milk in the pail. The water 

 container should be fitted with a grid or the bottom should be 

 fluted so that the water may circulate freely under the pails. 

 The same object may also be achieved by standing the pails on a 

 flat surface if their lower rims are provided with holes. The water 

 inlet pipe should reach the bottom while the overflow should be 

 at the top. On large farms it is best to have a tank above the 

 cowshed, which is filled just before milking, and from which the 

 water slowly flows through wooden troughs situated on the coolest 

 side of the shed ; the cooling may thus be started during the 

 straining process. The pails are first placed in the end of the 

 trough nearest to the outlet and are moved by degrees towards 

 the inlet end, whence they are removed from the trough. The 

 troughs must be covered over by a lean-to roof sufficiently high to 

 allow a man to stand under it. The used cooling water may with 

 advantage be used for drinking water for the cows. When the 

 milk has been cooled to the temperature of the water, it may be 

 further cooled by standing the pails in ice water or by passing it 

 over a cooler through which a mixture of four parts of ice in small 

 lumps and one part of salt is circulated. In summer time the 

 cooler may be moved out into the fields, though if this is done the 



