PASTEURIZING MILK. . 5 
tion of each process, and to present preliminary data on the cooling 
of milk in bottles by an air blast. 
METHOD OF BACTERIOLOGICAL ANALYSIS, 
Since bacterial counts are widely influenced by differences in media 
and incubation it is always essential in discussing the results of bac- 
teriological work to explain exactly how the counts were obtained. 
In this work plain infusion agar, made according to the recom- 
mendations of the committee on milk analysis (6), was used. The 
plates were incubated for five days at 30° C. (86° F.) and counted. 
METHOD OF PASTEURIZING IN BOTTLES. 
Milk was placed in special bottles, similar to those supplied to the 
trade, and capped by machine with patented metal caps. The bottles 
were heated by being submerged in hot water at a temperature of 
from 145° to 147° F. After the temperature in the bottom of the 
bottles had reached 145° F. they were held at that temperature for 
30 minutes and removed, plates being made while the milk was hot. 
The bottles were so constructed that after a full quart of milk was, 
poured in there remained an air space of sufficient size to allow for 
the expansion during the heating. While heating it was noticed that 
the milk expanded and pressure enough was generated to lift the 
caps slightly so as to allow air to escape. Special care was taken to 
see that the temperature in the bottom of the bottle of milk was 
maintained for the full 30 minutes. 
The method of pasteurization was the same as is used on a com- 
mercial scale; hence, the results obtained are directly applicable to 
commercial conditions. The fact that the bacterial counts were taken 
directly after heating has no effect on the results, since it has been 
shown that cooling plays no part in the destruction of bacteria in the 
pasteurizing process (3). 
BACTERIAL REDUCTIONS BY PASTEURIZATION IN BOTTLES. 
It has been claimed that remarkable bacterial reductions have been 
obtained by pasteurization in bottles which were far superior to those 
obtained by other methods even when the same temperature and 
holding period were used. In order to determine what reductions 
could be obtained, 34 samples of milk were pasteurized in bottles. 
The results are seen in Table 1. The bottles for samples Nos. 2 
to 23, inclusive, were washed clean in hot water, but not steamed, 
before they were filled with raw milk. The bottles for the other 
samples were steamed two minutes and then cooled before they were 
filled with raw milk. 
