10 



The American Public Health Association 



ing to the cooler, but should be con- 

 nected to a "flow controller" same as 

 hereinbefore described that will not 

 permit the milk being drawn off at a 

 more rapid rate than the rate of fill- 

 ing. This "flow controller" must not 

 have a connection with the cooler dur- 

 ing the continuous operation, so that 

 in case any of the valves in the dis- 

 charge of the holding tanks should 

 leak, which is likely to happen at anj' 

 time, the milk that is seeping through 

 would not pass to the cooler and infect 

 the finished product. After the con- 

 tinuous operation of the milk flowing 

 direct from the holding tanks to the 

 cooler is finished, the "flow contru'iier" 

 at the discharge of the holding tanks 

 is connected to the cooler and the milk 

 drawn off. 



The temperature recording instru- 

 ment in the discharge of the continu- 

 ous flow holding tanks records the 

 temperature of the held milk, which 

 must be at or above the minimum 

 holding temperature, and also shows 

 the time of drawing off the tanks by 

 the interruption of the continuous flow. 



Continuous flow holding tanks have 

 no moving parts or moving valves, 

 stuffing boxes or coils, or pipe fittings, 

 or connections under pressure ; they 

 are easily cleaned and sterilized. 



(d) Coolers. The cooler for cool- 

 ing milk, after the holding period, 

 forming a part of either the intermit- 

 tent or continuous types of pasteuriz- 

 ing apparatus should haye the neces- 

 sary cooling surface to cool the vol- 

 ume of milk per hour to within two or 

 three degrees of the temperature of 

 the water circulated for cooling. It is 

 preferable to use water for cooling in- 

 stead of low temperature brine or di- 

 rect expansion of ammonia. With the 

 brine or direct expansion ammonia, it 

 is almost impossible to prevent a part 

 of the milk from being frozen. The 

 water for the cooler may be cooled by 



direct expansion, or by low tempera- 

 ture brine. 



In a continuous pasteurizing appar- 

 atus, milk heaters and coolers, when 

 properly constructed and proportioned 

 in relation to the quantity of milk to 

 be heated per hour, require the volume 

 of A\ater circulated to exceed the vol- 

 ume of milk by about 5 per cent. The 

 circulating water cooled from a normal 

 temperature to 38 degrees F. will cool 

 the milk at approximately 42 degrees 

 F., and with milk from the holder at 

 145 degrees F., the circulating water 

 will leave the cooler at 120 degrees to 

 125 degrees F., obtaining all the ad- 

 vantages of regeneration. This water, 

 when passed through a water heater, 

 using either exhaust or live steam, or 

 both, must be raised to about 149 de- 

 grees to 150 degrees F., which will, 

 A\'hen circulated through the heater, 

 heat the milk to 145 degrees F. This 

 water, when discharged from the 

 heater, can be run to the water storage 

 tank of the building and used for gen- 

 eral purposes. 



Sterilization of the cooler is neces- 

 sary, and the cooler must be constructed 

 to stand this process. To accom- 

 plish sterilization, steam at 10 pounds 

 pressure should be turned into the in- 

 side of the cooler and the apparatus 

 maintained under these conditions for 

 the time necessary to produce steriliza- 

 tion as determined on the condensa- 

 tion water drips from the bottom of 

 the cooler. In an open surface cooler, 

 the steam is turned into the water 

 thoroughfares after emptying, and 

 maintained under these conditions for 

 from one to two hours. The stress on 

 a cooler caused by sterilization comes 

 more from uneven expansion than 

 from pressure and a steam pressure of 

 10 pounds is ample. It is difficult to 

 sterilize a cooler not constructed to 

 withstand the application of this 

 amount of pressure, and the best way 

 of accomplishing what can be done in 



