THE BACTERIOLOGY OP ICE CREAM 195 



putting a clean and safe product on the market. The Iowa 

 Agricultural Experiment Station- in 1912 attempted the 

 manufacture of ice cream with a low bacterial count and suc- 

 ceeded, by using cream that had been properly pasteurized 

 and well cared for, other ingredients of high quality, and thor- 

 oughly steamed utensils, containers, and freezer, in producing 

 ice cream containing only a comparatively few bacteria. The 

 methods that were employed were selected with particular at- 

 tention to their practicability and can be used in any properly 

 equipped factory. The bacterial content of some of the lots 

 of ice cream is given below. 



Trial No. Bacterial content of ice cream 



1 6,300 per c. c. 



2 10,000 * 



3 4,200 " 



A procedure that has recently been tried out from the 

 standpoint of its influence on the bacterial count is the pas- 

 teurization and immediate homogenization of the mix either 

 shortly before or 24 hours before freezing. Some exception- 

 ally low count ice cream has been secured in this way, while 

 in other cases the count has not been quite so satisfactory; 

 the variation is, in all probability, due to the variation in 

 the resistance of the bacteria contained in the cream to the 

 pasteurization temperatures. The procedure involves the 

 pasteurization of all the ingredients that go into the ice cream 

 and not the cream alone. Moreover, it calls for less handling 

 after the pasteurization than the pasteurization of the cream 

 and the subsequent preparation of the mix. The procedure is 

 claimed by commercial men to possess certain advantages from 

 the standpoint of factory methods, and it seems that its ad- 

 visability from the standpoint of the wholesomeness of the 

 product cannot be questioned. The changes secured in the 

 numbers of bacteria during the procedure are shown in three 

 trials below. 



Bull. 134, p. 288. 



