THE BACTERIOLOGY OF 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 suec- 
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 
Sites ctaie, decieaeSiata Sie Dente eect e eter e ete ee ee eceeteeseseeees 6,300 DOr C. tu. 
IDE ie hie Gee tna hic Bea mB Ak ie BARNES in Se ss a wasn wg aman 10,000 es 
Sl BA aren teeta chalice ip kegs ib el dep aided ae sons 4,200 ae 
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. 
2 Bull. 134, p. 288. 
