THE BACTERIOLOGY OF ICE CREAM 



193 



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 16 

 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 17 concluded from their study of 12 samples that when 

 ice cream is kept frozen for periods of at least a month, there 

 is no marked increase or decrease in the bacterial count, as 

 shown by litmus lactose gelatin plate cultures. More recently 



16 Bull. 134. 



17 Bull. 83, Storrs Agricultural Experiment Station. 



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