8 



Tre American' Public Health Association 



from dumps and rubbish heaps, and 

 frequently containing very objection- 

 able and highly dangerous material. 



(3) Pasteurization with Intermit- 

 tent and Continuous Flow Apparatus. 

 Regeneration in a pasteurizer is an ex- 

 change of temperatures between the 

 hot and the cold milk, and is obtained 

 by an. apparatus that either brings the 

 flow of hot and cold milk on either side 

 of the metal surface whereby the hot 

 milk is cooled by the cold milk and 

 the cold milk is heated by the hot milk, 

 or by an apparatus that circulates 

 water first through the cooler, which 

 becomes heated by taking up the heat 

 of the hot milk. This water, after the 

 addition of the steam required to bring 

 it up to a temperature necessary to 

 heat the milk, is circulated thi-ough 

 the heater and raises the milk to the 

 pasteurizing temperature. The eco- - 

 nomic advantage of regeneration is ap- 

 parent, when it is considered that 

 water at 38 degrees F. may be run into 

 a cooler and be discharged from the 

 cooler at 120 degrees F., all the steam 

 then required to heat the milk is that 

 necessary to raise this water from 120 

 degrees to 150 degrees, at which tem- 

 perature the water will heat the milk 

 to 145 degrees. ,To accomplish this it 

 is necessary to have properly con- 

 structed and proportioned apparatus. 

 This system is of advantage only in 

 milk plants that have a run of several 

 hours' duration. If milk is being held 

 in the holders for thirty minutes for 

 the first half hour of the run, there is 

 no milk to cool, and on the last half 

 of the run, there is no milk to heat. 

 Regeneration is an economic advan- 

 tage only, and of no advantage to the 

 milk. It is a decided disadvantage, 

 when the apparatus is so constructed, 

 that the milk is forced through an ex- 

 tra device that has gasketed closures 

 or troublesome cleaning features. Ap- 

 paratus in which any possible mixing 

 by leaks or seepage between the hot 



milk and the cold milk in the milk 

 channels of the apparatus is improper 

 in construction and may destroy the 

 effects of pasteurization. 



In a continuous flow pasteurizing ap- 

 paratus, it is important to have the 

 supply of milk flow to the heater at a 

 uniform predetermined rate per hour, 

 proportionate to the capacity of the 

 apparatus, in order to maintain the 

 holding time, the heating temperature 

 and the cooling in co-ordination with 

 uniform flows of the heating and cool- 

 ing mediums. This uniform supply 

 flow cannot be properly maintained by 

 a pump, for, owing to the variations in 

 slippage and varying quantity of air in 

 the milk, a pump will not always dis- 

 charge the same amount of milk when 

 running at the same rate of speed. 



(a) Flow Controllers. A device 

 ■ termed a "flow controller," consisting 



of a small metal tank about thirty 

 inches in diameter by twelve inches 

 deep, with the milk supply pipe pro- 

 jected through the side arid having a 

 float to maintain a constant depth -of 

 milk in the tank and a fixed outlet of 

 proper area to discharge the amount 

 of milk wanted per hour, will maintain 

 a constant flow when the supply is suf- 

 ficient. The fixed outlet must dis- 

 charge into an open connection to pre- 

 vent syphonage. In the pasteurizing 

 installation the "flow controller" is 

 placed above the heater to which the 

 milk flows by gravity. 



(b) Heaters. It is important to 

 have the heater for the milk contain the' 

 necessary heating surface to raise the 

 temperature of the milk to 145 degrees 

 F., when running at full capacity and 

 using water not more than five or six 

 degrees higher as the heating medium. 

 With such a heater, overheating can- 

 not take place when the temperature 

 of the water is properly controlled, 

 even if the flow of the milk is reduced 

 for a time, as is often the case in plant 

 operation. A heater with a relatively 



