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 
Towa Agricultural Experiment Station’® 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 ec. ¢. respectively. The increases per 
ec. ec. 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 fill the machine since the 
water would not hold the air beaten into it and thus failed to 
inerease 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 oue washing until the 
next freezing because of the probability of the rapid multipli- 
cation of bacteria in this. Steam should be used with great 
cere on a freezer, and if the freezing chamber is steamed, 
% Unpublished data, 
