COOLING HOT-BOTTLED PASTEURIZED MILK. 37 
than if the milk were cooled immediately to the same temperature. 
In fact, in our experiments, on a 30-crate basis, there. was a marked 
reduction in the bacterial numbers during the cooling period, 
especially when the raw milk contained large numbers of bacteria 
before pasteurization. From our experiments it seems that pas- 
teurized milk can be cooled, on a commercial scale, from 145° F. 
(62.8° C.) to 50° F. (10° C.) by means of forced-air circulation within 
three hours; consequently the process can be completed well within 
the 5-hour limit. In order to have a wide margin of safety and to 
obtain the best results, we recommend that the cooling process be 
started immediately after the hot pasteurized milk is bottled and 
that it be completed within three hours. 
The cooling of milk is absolutely essential in order to restrain 
bacterial growth, and we wish to emphasize the fact that the process 
of cooling slowly does not eliminate the cooling process, but simply 
makes use of a slower-cooling process than is in use at the present 
time. 
9. So far as our laboratory experiments on a 30-crate basis in- 
dicate, slow cooling of hot-bottled pasteurized milk has no appreciably 
detrimental effect on the cream line and the flavor of the milk. This 
is true for periods of cooling of not more than three hours. It is, 
of course, possible that different results may be obtained on a large 
commercial scale. 
10. On account of the uneven heating of pint and quart bottles 
in similar positions, and the same-sized bottles in different position 
in the stacks, attempts to heat milk in bottles by means of forced- 
air circulation were not successful. It was found impossible to heat 
the bottles to the pasteurizing temperature of 145° F. (62.8 C.) 
without overheating some of them. 
CONCLUSION. 
Our results indicate that it is commercially practicable to cool hot 
pasteurized milk in containers not larger than quart bottles by forcing 
cold air downward over them when the air is at a temperature of 40° 
F. (4.4° C.) or lower. 
On account of overheating portions of the milk, the process of 
pasteurizing milk in bottles by forcing hot air over them seems com- 
mercially impracticable. 
This bulletin contains experimental data on the method of cooling 
hot-bottled milk by forced-air circulation which we believe will be 
of assistance in the practical application of this method of cooling. 
When the temperature of the outside air is 40° F. (4.4° C.) or lower, 
it may be used for this purpose, but when it is higher than that it 
must be cooled b} r mechanical refrigeration. It is possible to use a 
combination of outside air and refrigerated air; that is, outside air 
