190 UNIVERSITY OF WISCONSIN STUDIES 



been the cause of large numbers of bacteria in the product 

 of a certain ice cream plant. 



(2) Outside Contamination 



Air. Air plays a part in the contamination of practically 

 all dairy products although apparently this contamination is 

 less serious than it was at one time supposed to be. In an ice 

 cream plant, as in most dairy establishments, the moisture on 

 the floors, walls and ceiling must tend to materially reduce 

 contamination from this source. With wide-open windows and 

 a dust ladened air blowing in, it is conceivable that air con- 

 tamination might be of considerable consequence but under 

 ordinary conditions this is certainly not true. 



Utensils. Utensils undoubtedly are as important a source 

 of the contamination of ice cream as they are of other dairy 

 products, and always should be given the best of care. The 

 Iowa Agricultural Experiment Station 13 determined the con- 

 tamination from a freezer by adding sterile water to the ma- 

 chine and then operating the freezer for about the freezing 

 period, after which the bacterial content of the water was de- 

 termined. Although the freezer was one that was given more 

 than ordinary care, the counts in 5 tests were 3,700; 141,500; 

 8,050 ; 1.195 ; and 300 per c. c. respectively. The increases per 

 c. c. of an ice cream mix would have been considerably more 

 than in the case of the water because it was necessary to use 

 an excessive amount of water to nil the machine since the 

 water would not hold the air beaten into it and thus failed to 

 increase in volume. From these results, it seems evident that 

 the careful ice cream manufacturer should study his process 

 with the idea of reducing the contamination from the various 

 utensils used. Because of its construction the freezer should 

 be given particular attention ; small amounts of water should 

 not be allowed to stand in it from one washing until the 

 next freezing because of the probability of the rapid multipli- 

 cation of bacteria in this. Steam should be used with great 

 care on a freezer, and if the freezing chamber is steamed, 



13 Unpublished data. 



