MILK-PLANT OPERATION. 5 
In order to pasteurize milk properly, two things are necessary: 
1. The milk must be heated to 145° F. and held for 30 minutes 
with an accurate control of the temperature and time. After heating 
and holding, the milk must be immediately cooled to 50° F. or below. 
2. All apparatus which comes in contact with the milk must be 
cleaned thoroughly and sterilized after each using. 
Unless there is an automatic temperature control the steam and 
water valves must be carefully watched in order to maintain the proper 
temperature. If the milk is not heated to the proper temperature 
and held at that temperature, good results can not be expected. 
All pipes or " pockets" in which milk is held during the pasteurizing 
or holding process should be insulated, as otherwise the holding tem- 
perature can not be maintained. Great care must be used also that 
none of the valves leading from the heater or holder leak. Milk 
coming from the pasteurizer should never pass through any apparatus 
which has contained raw milk. 
The cleansing and sterilizing of the apparatus is absolutely essen- 
tial for good results. All milk pipes, pumps, and filler valves, as 
well as the pasteurizer, should be taken apart after each run, thor- 
oughly cleaned and rinsed, and then sterilized by steam. An abun- 
dance of steam should be used. Unless all bottles and cans are 
thoroughly cleansed and sterilized the value of the pasteurization 
will be greatly reduced. 
The proper pasteurization of milk is a simple operation and there 
is little excuse for the poor results that are obtained at some plants. 
Poor results are usually not the fault of the type of pasteurizer 
used, but of the way in which it is operated. 
Following are some of the causes of poor pasteurizing results at 
milk plants : 
Pipes and pumps not cleaned and sterilized. 
Filler and valves not cleaned and sterilized. 
Milk rushed through the apparatus too fast. 
Milk not heated high enough nor held long enough. 
Temperature recorder not accurate. 
Bulb thermometer not accurate. 
Raw milk added to pasteurized milk in vat before the pasteurized lot is all drawn 
out. 
Pumps and piping not of sanitary construction. 
Leaky or inaccurate valves, which allow some of the milk to get through the appa- 
ratus without being held the proper length of time. 
Formation of foam in the holder. 
Great care should be taken that valves in the pipe line do not 
leak. Leaky valves are a very common occurrence in many milk 
plants, and besides the very insanitary character of such a con- 
dition much loss of milk results from it. The prevention of milk 
loss is an important part of the manager's duties, and no pains 
should be spared to keep all valves and connections in the milk 
lines tight. 
CONTROL OF PASTEURIZING TEMPERATURE. 
One of the most important considerations in the proper pasteuriza- 
tion of milk is control of the temperature. In order to do this 
properly an automatic device is necessary. It is difficult and often 
impossible to control the temperature by means of hand valves, 
but there are on the market automatic devices which will control 
the temperature very accurately. 
