18 



BULLETIN 744, U. S. DEPARTMENT OP AGRICULTURE. 



HOW TO COOL MILK QUICKLY. 



Much of the market milk for our large cities reaches the railroad 

 station in the country for shipment at a temperature of about 60° F., 

 and some is as high as from 80° to 90° F. At least one of our large 

 cities obtains milk from a territory 400 miles away. It is evident, 

 therefore, that milk on such a journey to the city has a considerable 

 time in which to deteriorate in quality. The higher the tempera- 

 ture of the milk the sooner it will deteriorate. Because of the 

 shortness of time between milking and the time of shipping, it is 

 usually impracticable to cool all milk to below 50° F. on the farm 

 by the use of a milk-cooling tank alone. Some sort of surface cooler 

 must be used in addition if the milk is to be cooled to 50° F. before 

 shipment. A surface cooler properly used with a supply of cold run- 

 ning water greatly reduces the quantity of ice needed in cooling milk 



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Fig. 13. — Time required to cool a 10-gallon can of milk to 50° F. under various con- 

 ditions. Milk not precooled. 



to a definite temperature, and also insures more rapid cooling. Un- 

 fortunately much of the running water used in surface coolers be- 

 comes warmer before use, either by allowing it to flow above the sur- 

 face of the ground, as from a spring, or by taking it from a storage 

 tank exposed to the sun. 



It is possible, by using a surface cooler to best advantage, to cool 

 the milk to within 2 or 3 degrees of the temperature of the water. 

 The colder the water, therefore, the more effective will be the cooling. 

 A series of tests was conducted with water at different temperatures 

 in order to determine the length of time necessary to cool milk to 

 50° F. In each test a 10-gallon can of milk was used. The milk was 

 placed in an insulated tank containing from 75 to 80 gallons of 

 water. Tests were conducted with water at 70°, 60°, 55°, and 50° 

 F., respectively, and in each test a 300-pound block of ice was placed 



