ICE CREAM MAKING 523 



degree rise in temperature. And added to these facts is another 

 equally ns important, namely, that it is next to impossible to 

 cool the air of a refrigerator with ice much below 50°, while 

 the common temperature is about 55°, which must be looked 

 upon as merely the lower limit of normal souring, at which the 

 growth of lactic acid bacteria will be slow but certain. On the 

 other hand, the temperature of water in which a few large chunks 

 of ice are floating will be found to range from 34° to 38°. Thus 

 cream set away to mature, yet to keep sweet, will not only cool 

 much faster but also to a lower point if water is employed. This 

 system, when a well-insulated tank is used, is not only the most 

 efficient, for the reasons just given, but also the most economical 

 of ice for the reason that practically all of the cooling power of 

 the ice (that is, both the latent and the specific cold, if one may 

 use the reversal term, which, though perhaps coined, serves 

 admirably the present need), will be employed for useful pur- 

 poses instead of being largely wasted, as is the case when the 

 cans of cream are merely packed close in a corner and buried 

 with broken ice. When this is done, as is so often the case, 

 the can is largely surrounded merely by cool air, and the ice 

 cold water formed by the melting ice runs away to the sewer, 

 still capable, however, of having done much good, quick work. 

 Acidity. 



The acidity of the cream has no effect on the swell of the ice 

 cream produced, until it reaches such a point as to cause the 

 cream to become brittle, when a lessened yield will result. 

 It becomes sour to the taste and smell long before the yield will 

 be affected. Either natural, or added commercial, lactic acid 

 seems to improve the body and texture slightly. A cream con- 

 taining 0.50 per cent or even 0.60 per cent acid will make a good 

 looking and good feeling ice cream, and, except for the sour 

 taste, will be as satisfactory an article as could be desired. The 

 sour flavor, however, will be detected if the cream possesses 

 more than 0.26 per cent or 0.27 per cent of acid, and it is un- 



