PASTEURIZING MILK. . 3 



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 cti 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. 



