186 UNIVERSITY OP WISCONSIN STUDIES 



cent, acid-forming: 38.03 per cent, inert 4.81 per cent, alkali- 

 forming 5.42 per cent and peptonizing 20.90 per cent. In 

 general these were high count ice creams and would be ex- 

 pected to show a considerable percentage of acid producing 

 organisms. 



The occasional presence of pathogens in ice cream is evi- 

 dent from the cases of disease that have been traced to this 

 product and is to be expected, due to the presence of these 

 types of organisms in cream. 



It is evident that ordinarily the types of bacteria found in 

 ice cream are determined practically entirely by the sanitary 

 quality of the materials used and by the handling given and 

 that the range in flora is limited only by the extent of varia- 

 tion that is possible with these. 



THE SOURCES OF THE BACTERIA IN ICE CREAM 



The bacteria that are present in ice cream come from two 

 main sources: (1) the materials used and (2) outside con- 

 tamination. 



(1) The Materials Used 



Cream. The cream used in the manufacture of ice cream 

 is quite likely to carry many bacteria unless pasteurization is 

 used, since ice cream manufacturers ordinarily buy cream 

 under conditions such that they have little, if any, control 

 over the methods of production. Commonly also considerable 

 difficulty is experienced in securing sufficient sweet cream; 

 this is particularly true during the hottest months when the 

 demands on the manufacturer are heavy. Accordingly, the 

 ice cream factories in certain sections are sometimes virtually 

 forced to accept cream with practically no other requirement 

 than that it be sweet and, in certain cases, the ice cream sold 

 is ample evidence that this requirement is not rigidly adhered 

 to. A portion of this cream is shipped without refrigeration 

 facilities and, although pasteurization before shipment is quite 

 common, it inevitably arrives at the ice cream factories with 

 enormous numbers of bacteria. 



