126 THE CREAMERY PATRON'S HANDBOOK. 



milk will flow over the cooler in about twelve or fifteen minutes and lose 

 from twenty to twenty-five degrees of heat by simply using the ordinary 

 well water. The same can if set into a tub of water at the same tempera- 

 ture would require from one hour to one hour and a half to accomplish the 

 same result. 



The effectiveness of a cooler depends upon the area of exposure and 

 the degree of coldness that may be maintained within itself to abstract 

 the heat. No cooler will abstract more heat than it gives off. If one hundred 

 pounds of freshly drawn milk passes over it and gives off twenty-five 

 degrees of heat, it will necessitate that one hundred pounds of water be used 

 at a temperature of fifty degrees. If it is desired to cool the milk more 

 than twenty-five degrees it will require a greater proportion of water. To 

 cool one hundred pounds of milk on a cooler will require as much water 

 to cool it standing in a tub, less the amount of loss from radiation 

 due to the longer exposure. The surface exposure of the ordinary shot- 

 gun can is 440 square inches, and eight gallon milk can is 872 inches, but the 

 layer of milk in contact with the surface is not changed rapidly. 



A series of tests were made of the cooling of milk as set in the ordinary 

 can and set in the tub, by suspending thermometers at distances of one inch 

 from the surface to the center. The milk was not agitated and the cool- 

 ing was more uniform than was anticipated. Milk seems to be a better 

 conductor of heat than water, and while the difference in temperature of 

 the water on the outside and the milk on the inside was quite marked, cur- 

 rents were set up that made the cooling quite uniform. When this differ- 

 ence in temperature became less pronounced the currents almost ceased 

 and further reduction was very slow. 



The special advantage to be derived from the use of the cooler is not 

 so much in the economy of ice or water used, as is so often claimed by the 

 manufacturers, but in the sudden chilling of the milk and thus arresting 

 bacterial growth. The sudden reduction of temperature seems to have 

 the effect of shock and checks the power to multiply. The reduction of 

 temperature to the same degree, but by slow means, is not so effective. 

 The same principle is recognized in pasteurizing; it does not depend simply 

 upon the raising the temperature to a high degree, but almost to the same 

 extent upon its sudden lowering. In the ordinary method of cooling milk by 

 setting the cans in tubs of water, the time of cooling is nearly two hours, 

 sufficient time for considerable multiplication. A second advantage in 

 the use of special coolers is in the aeration, the getting rid of much animal 

 odor and absorption of oxygen that has a detrimental effect upon some 

 forms. A study was made upon the number of bacteria present in milk 

 at every hour during forty-eight hours, using milk that had not been cooled, 

 milk that had been cooled and left at room temperature, and milk that 

 had been cooled and kept cool. The room temperature was ninety-three 

 degrees and the cooling was done to fifty-four degrees, as that was the water 

 temperature without the use of ice. The results often showed as much 



