THE BACTERIOLOGY OF ICE CREAM 198 
ee A ee 
aT eo 
rin Bacteria in frozen Bacteria in hardened Per cent change 
oO. ice cream ice cream in numbers 
Per e. ¢. Per ¢. ¢. 
1 2,270,000 1,660,000 —27 
2 2,120,000 1,105,000 —48 
3 4,700,000 5,200,000 +11 
4 33,500 21,000 —37 
5 30,500 30,000 eee 4 
6 21,000,000 5,320,000 —75 
7 268,500 246,000 —s 
In general the hardening of frozen ice cream caused a 
lowering in the bacterial count, as determined by the plate 
method, due presumably to the destructive action of the 
lowered temperature. The slight increase in a small percentage 
of the cases was in all probability due to experimental error, 
as a multiplication of the organisms was very improbable and 
care was taken to prevent contamination. 
The influence of holding on the bacterial content, of ice 
cream is of a great deal of importance from the standpoint 
of bacterial standards. Unless definite information regarding 
what can be: expected to happen to the bacterial content of 
ice cream during storage is available, bacterial standards can- 
not justifiably be instituted because holding ice cream un- 
doubtedly has some influence on the numbers of bacteria con- 
tained. In 1912, the Iowa Agricultural Experiment Station"® 
reported data on a number of samples which showed that 
in all probability there is a decrease, or else very little change, 
in the bacterial content of ice cream during storage and 
pointed out certain objections to results that had been pre- 
viously presented with the idea of showing an increase in the 
numbers of bacteria in ice cream during holding. Esten and 
Mason‘? coneluded from their study of 12 samples that when 
ice cream is kept frozen for periods of at least a month, there 
is no marked inercase or decrease in the bacterial count, as 
shown by litmus lactose gelatin plate cultures. More recently 
1 Bull. 134. : : 
17 Bull, 83, Storrs Agricultural Experiment Station. 
13 
