THK BACTERIOLOGY OF ICE CREAM 189 



this can be very important as the best practice prohibits the 

 use of excessive heat on account of its effect on the solidifying 

 property of the gelatin and the bacteria present in dry gelatin 

 must have considerable resistance or the desiccation to which 

 they have been exposed would have destroyed them. The 

 bacterial flora of gelatin is, to all appearances, made up largely 

 of spore formers, and the number of organisms per gram is 

 presumably closely related to the sanitary quality of the 

 material from which the gelatin was made. High grade gelatin 

 can be secured which has a negligible influence on the bacterial 

 count while certain gelatins may add large numbers of bacteria 

 to the ice cream mix and are to be avoided in the manufacture 

 of the highest quality product. 



Sugar. If sugar is properly protected its bacterial content 

 is practically certain to be very low, but it is entirely probable 

 that where sugar is exposed to dust and dirt it may be of 

 some little consequence as a means of contaminating an ice 

 cream mix. The results secured on plates indicate that the 

 great majority of the bacteria are spore-forming types. 



Vanilla. The Iowa Agricultural Experiment Station 11 has 

 examined five samples of vanilla and found the bacterial 

 content ranging from 200 to 2,300 per c. c. The alcohol 

 present in vanilla extract is undoubtedly responsible, in part 

 at least, for the low bacterial content and moreover this makes 

 it reasonably certain that vanilla is never an important source 

 of the bacteria present in ice cream. 



Condensed Milk. Condensed milk, usually the bulk con- 

 densed, is used in enormous quantities in many ice cream 

 plants. The product at the time of its use has been found by 

 the Iowa Agricultural Experiment Station 12 to contain large 

 numbers of organisms in certain cases. Excessive numbers 

 of organisms are in part caused by defective shipping and 

 holding methods and in some cases perhaps by a poor quality 

 of material from which the condensed milk is made. Bulk 

 condensed milk has been found in at least one instance to have 



11 Bull. 134, p. 287. 



12 Unpublished data. 



