HIGH AGING TEMPERATURES FOR ICE CREAM 3 



W right (^) studied the effect of initial cooling temperatures on the behavior 

 of gelatin in an ice cream mix and in skim milk. After homogenization the ice 

 cream mixes were cooled rapidly to the desired initial aging temperatures and 

 then were placed in storage (40° F.) where they cooled very slowly without 

 agitation to approximately storage-room temperature. Under those conditions' 

 no definite conclusions could be drawn as to the effect of high initial aging tem- 

 peratures for varying periods of time because the temperature was not controlled 

 during the initial aging period. However, this work showed that the rate of 

 cooling an ice cream mix immediately after homogenization greatly influenced 

 the behavior of the gelatin in the mix. ■. . 



PLAN OF EXPERIMENT 



The general plan of this investigation was to age one portion of an ice cream 

 mix at 68° and the other portion at .18° F. and make comparisons on the following 

 points: bacterial growth, titratable acidity, H-ion concentration, basic viscosity, 

 whipping ability, body and texture, melting resistance, and melting appearance. 



The high temperature (68° F.) was used in two ways: (1) as an initial aging 

 temperature for 4 hours, followed by a low temperature (.?8° F.) aging period of 

 20 hours; (2) as the only aging temperature for a period of 4 hours. However, 

 in the latter method the mix was cooled to 38° before it was placed in the freezer. 

 The 68° aging period remained constant at 4 hours, except for the first experiment, 

 in which the effect on bacterial growth, pH and titratable acidity was studied. 

 The aging periods for the control mixes (38°) were always equal to the total 

 aging period of the mixes aged at 68°. 



The influence of varying the gelatin content and the mix composition on the 

 magnitude of the effects of aging at a high temperature was also studied. 



Experimental Methods 



Since the ingredients and composition of the mix varied in this study, the 

 description of the mix is given for each experiment. The gelatin used was a mixture 

 containing samples of approximately 175 Bloom strength which were obtained 

 from nine gelatin manufacturers. The three sources of gelatin, namely, calf skin, 

 pork rind, and ossein, and also the various processes for manufaturing gelatin, 

 were represented. This composite sample tested 176 (Bloom strength) with 

 pH 5.25. 



Mixes were pasteurized at 145° F. for 30 minutes and homogenized at 2500 

 pounds pressure at the temperature of pasteurization. In preliminary trials small 

 batches were pasteurized in ice cream cans set in hot water and cooled by setting 

 the cans in cold brine. The small batches were aged at 68° in a thermostatically 

 controlled incubator and at 38° in the cooler. The preliminary trials were checked, 

 using batches ol approximately 300 pounds which were pasteurized in a commer- 

 cial pasteurizer and cooled over a surface cooler. These large batches were aged 

 at 68°, either in the holding tank or by setting 40-quart milk cans in water, and 

 aged at 38° in the cooler. 



The preliminary mixes, one-half gallon in size, were frozen in an experimental 

 brine freezer which is similar in mechanical construction to a commercial brine 

 freezer. The preliminary experiments were checked by freezing in a 40-quart 

 brine freezer. The brine temperature varied from +2° to — 5° F. Freezing 



