188 UNIVERSITY OF WISCONSIN STUDIES 



Ordinarily cream is one of the very important sources of 

 the bacteria in ice cream. It is possible that with a very 

 high grade cream and with some other ingredient of a poor 

 quality the cream may be over-shadowed as a source of 

 the bacteria, but this is rarely, if ever, the case under practical 

 conditions. The extent to which cream may contaminate ice 

 cream varies from the enormous number of bacteria con- 

 tributed by a raw cream on the verge of souring to the small 

 number added by a high grade cream, properly pasteurized 

 and stored. By the employment of proper pasteurization and 

 storage, the contamination from the cream can be controlled 

 and when the added safety to the consumer is considered there 

 is no justifiable objection to ordinances requiring the pasteuri- 

 zation of cream used in the manufacture of ice cream. 



The homogenization of cream is becoming more and more 

 common and is playing a very important part in well regu- 

 lated ice cream manufacture. Ordinarily homogenization in- 

 creases the bacterial content of cream, as determined by the 

 plate method, and this is presumably due to a breaking up 

 of the clumps of bacteria just as is the increase due to the 

 clarification of milk. The extent of the increase with homo- 

 genization is very variable and undoubtedly depends on the 

 numbers and types of the clumps present. When a homo- 

 genizer is used it should be given careful attention or it may 

 become an important source of contamination because of the 

 difficulty of cleaning. 



Gelatin. Gelatin may or may not be an important source 

 of the bacteria in ice cream. Gordon 9 has published the bac- 

 terial contents of 20 samples of gelatin where the results ran 

 from 200 to 30,000,000 per c. c. and the Iowa Agricultural 

 Experiment Station 10 studied 5 samples and found the counts 

 varying from 35 to 113,000,000 per gram; from these data it 

 is evident that the bacterial content of gelatin is extremely 

 variable. The heating to which gelatin is subjected in order 

 to get it into solution before its addition to an ice cream mix 

 may destroy some of the bacteria, but it does not seem that 



9 Ice Cream Trade Jr., p. 33, Jan., 1912. 



10 Bulletin 134, p. 286. 



