192 UNIVERSITY OF WISCONSIN STUDIES 
Trial Bacteria Bacteria in frozen Per cent change 
No. in mix ice cream later in numbers 
Pere. ec. Perc. ¢. 
1 19,100,000 24,750,000 +30 
2 2,220,000 2,270,000 +2 
3 30,000 33,500 +12 
4 485,000 660 ,000 +36 
5 27,500 45, 500 +65 
6 5,600, 000 4,700,000 —16 
7 270,000 285,00) +6 
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 
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 inerease varying from 7 to 22 per cent 
(Av. 13.8 per cent). Illustrative results follow: 
1©TInpublished data. 
