192 



UNIVERSITY OP WISCONSIN STUDIES 



From the results obtained it is evident that freezing com- 

 monly increases the apparent bacterial content of ice cream 

 and it seems reasonable to assume that this increase is due to 

 the breaking up of the clumps of bacteria as a result of the 

 agitation in the freezer. The lowering of the temperature in 

 all probability causes the destruction of some of the organisms, 

 and in those mixes in which there are few or no clumps the 

 lowering of the temperature may be of greater significance in 

 determining the change in numbers, as a result of the freezing, 

 than is the agitation. 



The hardening of ice cream that has just come from the 

 freezer involves a further decrease in temperature and this 

 would ordinarily be expected to have an influence on the bac- 

 teria contained. Ice cream usually leaves the freezer at a tem- 

 perature of 26 to 28 F. and is then reduced to a temperature 

 usually below 10 F. by using either ice and salt or a refrig- 

 erated room. The effect of this lowering in temperature has 

 been studied by the Iowa Agricultural Experiment Station 15 

 in 52 comparisons of the bacterial content of the frozen ice 

 cream before and after hardening. In 1 case (2 per cent) 

 there was no change in numbers during the hardening; in 

 45 cases (86.5 per cent) there was a decrease, varying from 

 2 to 75 per cent (Av. 39.1 per cent), while in 6 cases (11.5 

 per cent) there was an increase varying from 7 to 22 per cent 

 (Av. 13.8 per cent). Illustrative results follow: 



15 Unpublished data. 



