2 BULLETIN 340, U. S. DEPARTMENT OF AGRICULTURE. 



It is evident from the report of Gerber and Wieske (2) that pas- 

 teurization in bottles has been practiced in certain localities for a 

 considerable period of time. According to these authors, pasteuri- 

 zation in bottles by the process of Gerber. which consists of heating 

 milk in bottles for one hour at 65° C. (149° F.). during which they 

 are agitated, had been practiced in certain dairies for 15 years pre- 

 vious to 1903. 



In this country milk has been pasteurized directly in bottles at 

 various Strauss infant milk stations for several years, but this proc- 

 ess has not been used on an extensive commercial scale until within 

 the last two years. During the summer of 1910 an investigation was 

 started of the bacteria which survived pasteurization in flasks and 

 of the efficiency of the process. A report of this work has been pub- 

 lished in Bulletin 161 of the Bureau of Animal Industry (3). 



While this work was in progress North (4) suggested the pasteuri- 

 zation of milk in bottles on a commercial scale by the use of machines 

 similar to those which have been in use in breweries for several years. 



The process of pasteurizing in bottles consists in bottling the milk 

 in specially constructed bottles of sufficient size to allow a space in 

 the top of the bottle to take care of the expansion of the milk during 

 heating. The bottles are capped with special water-tight caps and 

 submerged in hct water. After the milk in the bottles has reached 

 the pasteurizing temperature, the temperature is maintained for 30 

 minutes ; the hot water is then replaced by cold and the milk cooled. 

 In general it takes about 30 minutes to heat the bottles, 30 minutes 

 for the holding period, and 30 minutes to cool. Milk is also pas- 

 teurized in the bottle by heating and cooling with water which is 

 sprayed over the bottles. By this method of spraying, ordinarj^ 

 caps with a protective covering can be used; this will be described 

 in another place in this bulletin. 



This process of pasteurizing in bottles is now used on a commer- 

 cial scale in a number of milk plants throughout this country. 



Numerous advantages of this method of pasteurization over the 

 ordinary methods have been claimed particularly in relation to the 

 far superior bacterial reductions obtained. The most obvious point 

 of advantage of this process is the prevention of reinfection after 

 pasteurizing, but it seems as though a modification of the present 

 system of "holder" pasteurization by bottling the pasteurized milk 

 while hot, as suggested previously by the senior writer (.">). would 

 help to solve the problem of reinfection. 



Accordingly, the general object of the work hereinafter described 

 has been to compare on a laboratory scale pasteurization in bottles 

 with the process of bottling hot pasteurized milk. The special ob- 

 jects have been to determine the bacterial reductions in each process, 

 to study any special points which must be considered in the opera- 



