THE BACTERIOLOGY OF ICE CREAM 187 
Under the condition usually prevailing, the modern ice 
cream manufacturer finds it very necessary to pasteurize the 
cream which he receives. This is necessary because he has no 
control over the production and desires to put out a product 
containing no living pathogens and also because he wishes 
it to have satisfactory keeping qualities, as it is ordinarily 
uecessary for him to hold it at least a short time. The pasteur- 
ization of cream is usually followed by aging in order that 
the ice cream maker may secure the most desirable yield and 
texture. The length of the aging depends, under commercial 
conditions, on the demand for ice cream and on various other 
factors over which the manufacturer has little or no control. 
It is usually considered that 48 hours is a sufficiently long 
aging period, but this may be reduced due to a heavy demand 
or lengthened as a result of cooler weather. The holding of 
the cream can be accomplished without an increase in the 
bacterial content by the use of proper methods. If the pasteur- 
ization is followed by prompt cooling to 32° F. or slightly 
below (e. g. until a half inch layer of cream freezes to the 
wall of the storage tank) there will be no multiplication of 
the bacteria for a considerable period of time. From the re- 
sults secured on the storage of cream at 32° F. by the Iowa 
Agricultural Experiment Station’ and from data secured by 
various investigators on milk held at this temperature, it 
seems that even under very favorable conditions cream should 
not be held for more than a week, since there are certain 
bacteria that will grow in cream at this comparatively low 
temperature. For the storage of cream, the use of tempera- 
tures which will freeze the cream has been suggested in con- 
nection with agitation during the cooling process. Such a pro- 
cedure would be expected to prevent the separation of the 
solids that occurs when milk or cream is frozen without agi- 
tation and may eventually prove widely practical, particularly 
when the cream or the ice cream mix is to be homogenized. 
The use of temperatures below the freezing point would make 
possible the storage of cream for extended periods of time’ 
without an increase in the bacteria contained. 
8 Bull. 134, p. 285. 
