ICE CREAM MAKING 517 



measured by the thermometer, nor changing its apparent condi- 

 tion. This stationary condition of the mix, in practice with 

 batch machines, will continue for four to fifteen minutes, de- 

 pending on the rate of the freezing. It is during this time that 

 the latent heat is being extracted from the cream and transferred 

 into the ice, melting it. The swell, though beginning at about 

 34, is by far the most rapid near the end of this apparently in- 

 active period. In fact just before the material fully freezes, the 

 increase is surprisingly rapid. At about this time the tempera- 

 ture drops to 27 and the cream becomes brittle and ceases 

 swelling altogether. At 28 to 27 the product is ready to 

 remove from the freezer. 



Now, the rate at which cream cools depends on several fac- 

 tors, chief among which are : the temperature and rate of flow 

 of brine (brine freezer), or the amount, proportion, and size 

 of salt and ice (ice freezer) ; the relation of the mass of these 

 to the mass of cream being cooled ; the surface exposed for cool- 

 ing action ; and, finally, the difference in temperature between 

 the cream and the freezing agent. 



For example, 10 pounds of ice, 1 pound of salt, and 1 quart of 

 water produce a brine of about 21 in temperature. This, 

 acting upon 6 pounds of mix at a temperature of 70, cooled it 

 about 20 the first minute and 10 the second minute, yet slowed 

 down continually so that it required a full minute to lower the 

 temperature from 30 to 29. So far as the swell is concerned, 

 however, it practically all takes place during the time, be it 

 ten minutes or twenty, in which the cream is dropping through 

 the successive Fahrenheit temperatures from 34 to the end of 

 the 29 period. 



The maximum of swell is reached at the point of thorough 

 freezing (about 28| F.) ; but if the ice cream is drawn or dipped 

 away at this critical point the warmth of the air and the tools 

 tends to melt it somewhat, especially where it lies against the 

 walls of the holding can. When this melted matter again 



