16 



The American Public Health Association 



b}' means of a separate pump. If the 

 raw milk pump is used, it will infect 

 the heated and held milk unless^ it is 

 washed and sterilized during the op- 

 eration. Pasteurizing apparatus should 

 be so installed that all parts will drain 

 through the whole system at the finish 

 of the run, otherwise, the milk left in 

 the apparatus will be neither raw nor 

 pasteurized and must be utilized as a 

 b3--product. The public are placed in 

 jeopardy of receiving watered milk 

 when water is used to' force the milk 

 out of the apparatus at the finish of 

 the run and such practice should be 

 prohibited. A proper installation of 

 apparatus will obviate this condition. 



(f) That, in which foam developed 

 by the milk movement, floats on the 

 top of the milk while the milk is stand- 

 ing in the holding device, and owing 

 to the lack of effective insulation of 

 temperature maintenance, the tempera- 

 ture of the foam will drop below the 

 minimum holding temperature, which 

 is the same in result as lowering the 

 milk temperature and defeats efficient 

 treatment. 



(g) That, on account of pipe connec- 

 tions or other causes, permits any low- 

 ering of the temperature of the milk 

 in transit from the heater to the holder, 

 or lowering of the temperature of any 

 part of the milk while in the holder. 



(h) That does not have means to 

 prevent the emptying of continuous 

 holders at the finish of the run at a 

 more rapid rate of flow than the rate 

 of filling, thereby shortening the hold- 

 ing time of the milk in the tanks at the 

 finish. 



(i) That does not have an absolutelx- 

 safe device in the discharge outlets 

 from the holding tanks to the cooler 

 so that any leakage or seepage through 

 the milk cock in the pipe emptying the 

 holding tank, will flow out onto the 

 floor in view of the operator, so that 

 the leak may be remedied, instead of 



flowing to the cooler there mixing with 

 and infecting the finished product. 



(j) That has a steam or motor 

 driven pump, maximum speed of which 

 will force the milk through the holding 

 device at a rate that reduces the hold- 

 ing time of the milk below the min- 

 imum, or a purnp in which the rate of 

 flow depends on the judgment of the 

 operator to maintain the proper speed 

 in order not to supply milk to the 

 holding device at such a rate as will 

 reduce the minimum holding time. A 

 pump on account of variations in slip- 

 page and air in the milk does not pro- 

 duce a constant flow at a constant 

 speed. 



\'i. Analy'I'icai. Cuxtkdl ov P.VsriaT!!!- 

 ZATION Plants. 



This phase of the report includes a 

 discussion of the physical, chemical or 

 ph3'si co-chemical and biological methods 

 and procedure used to determine the 

 effectiveness of the pasteurization 

 processes. 



( 1 ) I'hysical jMethods. The purely 

 ph}-sical or mechanical methods of 

 supervisory control ha^■e been consid- 

 ered already but it may be well to men- 

 tion some of the important considera- 

 tions requisite to the adequate testing 

 of the efficiency of time and tempera- 

 ture recording devices. 



(a) Testing of Time and Tempera- 

 ture Recording Devices. Thermometer 

 tests on recording instruments to show : 

 comparisons at lo\\'est temperature on 

 chart, at highest temperature on chart, 

 at 130 degrees to 160 degrees F., ; de- 

 terminations to show rapidity of action 

 to sudden changes of temperature, 

 slight changes of temperature, changes 

 140 to 155 degrees F, ; effects on tem- 

 perature recording by changes in depth 

 of bulb and clock located as follows ; 

 bulb low-clock high, clock low-bulb 

 high, bulb and clock l('\'cl ; character- 

 istic of instruments — pririted chart 

 lines ma^• be too close, too heavv, in- 



