PASTEURIZING MILK. 5 
Four pint bottles and four quart bottles were used. The averaged 
temperatures in the pint bottles are shown in figure 1. It will be seen 
from the curves that in a pint bottle with water at 50° F. submerged 
in hot water at about 145° F. it took lOf minutes longer for the tem- 
perature in the bottom of the bottle to reach 140° F. after the top had 
reached that temperature and 4f minutes longer for the temperature 
in the middle of the bottle. When the temperature in the top of the 
bottle was 140° F., in the bottom it was only 118° F. 
The averaged temperatures of four quart bottles are shown in figure 
2. When the temperature in the top of the bottle was 140° F., that 
in the bottom was only 127° F., and it took 9J minutes longer for the 
temperature in the bottom to reach 140° F. 
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Heating period in minutes. 
Fig. 1. — Variations in temperature in different parts of pint bottles of water during the 
process of pasteurization in the bottle. 
It is evident that when pasteurizing in the bottle care must be taken 
to record the temperature in the bottom of a bottle and to date the 
holding period of 30 minutes from the time the bottom temperature 
has reached 145° F. In recording the temperature an accurate ther- 
mometer should be used, and it should reach to within one-half inch 
of the bottom of the bottle. 
COOLING THE MILK AFTER PASTEURIZING. 
After the milk is heated in bottles on a commercial scale it is 
cooled by replacing the hot water with cold and gradually changing 
the temperatures so as not to break the bottles. Upon cooling, the 
hot milk contracts and a partial vacuum is formed in the bottle when 
the caps are tight. It is recommended by the manufacturers of 
some of the patent caps that after heating the bottles be allowed to 
