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 

 necessary 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 8 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. 



'Bull. 134, p. 285. 



