20 



BULLETIN- 744, U. S. DEPARTMENT OF AGRICULTURE. 



previous experiment was, respectively, 2 hours and 10 minutes, 1 

 hour and 15 minutes, 43 minutes, and 20 minutes. In terms of ice 

 melted the precooling resulted in a saving of 11, 16, 19, and 22 pounds 

 of ice, respectively. 



An efficient way of cooling milk on a dairy farm is well illustrated 

 in figure 15. Warm milk that was not precooled was placed in a tank 

 containing water at 37° F. and was cooled to 50° F. in about an hour. 

 The same quantity of milk precooled with water at 55° and then 

 placed in a tank of ice water at 37° was cooled to 50° F. in 20 

 minutes. This illustrates an easy and rapid method of cooling milk 

 to 50° F. or below if ice is used. 



While, from a cooling standpoint, wooden tanks give good results, 

 an insulated concrete tank similar to the one shown in figure 1 is 

 more satisfactory for the dairy farm. A tank of that kind is not 



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Fig. 15. — Showing quick method of cooling milk with ice water. 



hard to construct, is very durable, and can be set partly in the 

 ground, which is an advantage in that cans can be lifted in and out 

 with less effort. 



THE USE OF ICE. 



For best results ice should be put into the cooling tank a sufficiently 

 long time ahead of the cans of milk to insure that the tank water is 

 at a low temperature when the cans of milk are set in. To insure 

 that milk is cooled to and is held at a sufficiently low temperature, a 

 cooling tank always should contain ice during hot weather. The 

 quantity of ice necessary depends upon the outside temperature, 

 the quantity of milk to be cooled, and the size, construction, and loca- 

 tion of the cooling tank. The quantity necessary for any given set of 

 conditions can be determined readily by putting a definite quantity 



