ANNUAL REPORT, 1932 27 



(3) When an ice cream mix containing 14 per cent fat, 10 per cent serum 

 solids, 15 per cent sugar, and 0.4 per cent gelatin (175 Bloom) was aged at 68° F. 

 for 4 hours, the efficiency of the gelatin was increased to such an extent that the 

 gelatin content could be reduced 0. 1 per cent without any loss in the quality of the 

 finished product. 



(4) Aging a pasteurized ice cream mix up to 6 hours at 68° F. had no effect 

 on bacterial growth, pH, and titratable acidity which would be of any commercial 

 significance. 



(5) When an ice cream mix containing gelatin was aged at 68°F. for 4 hours, 

 the basic viscosity was slightly decreased, but the basic viscosity was greatly 

 increased when the high temperature aging period was followed by a low tempera- 

 ture aging period, as compared with a mix aged only at 38° F. 



(6) When an ice cream mix containing no gelatin or other stabilizer was 

 aged at 68° F. for 4 hours, there was no marked effect on the consistency and whip- 

 ping ability of the mix or on the melting resistance, body, and texture of the finished 

 product. 



(7) When an ice cream mix containing the optimum amount of gelatin for 

 low temperature aging was aged at 68° F. for 4 hours, there was an excessive retar- 

 dation in melting and a curdled appearance on melting. This objectionable 

 melting behavior can be corrected by a reduction in gelatin without lowering the 

 quality of the finished product. 



(8) It is conceivable that in ice cream plants where the cooling of mixes is 

 not being carefully checked, mixes may be aged unintentionally for several hours 

 at a temperature above 50° F. This unintentional high aging temperature in all 

 probability is a big factor in causing the curdled appearance on melting which has 

 troubled some ice cream manufacturers but could not be explained. 



The Theoretical Causes of the Factors Involved in the High Initial 

 Aging Temperature Phenomena. (W. S. Mueller.) In order to find an 

 explanation for the structural changes in a gelatin gel, as a result of high aging 

 temperatures, a detailed study of the optical rotation of pure 1 per cent gelatin- 

 water solution was made. Gelatin-water solutions were aged at various temper- 

 atures (50°-r22° F.) for a period of four hours and then at 36° F. for a period of 

 44 hours. The control solution was aged at 36° F. only, for a total period of 48 

 hours. The optical rotation was determined after a total aging period of 24 hours 

 and 48 hours. The results so far obtained show that high initial aging tempera- 

 tures have no marked effect on the optical rotation after a total aging period of 24 

 and 48 hours when compared to an identical solution aged at 36° F. only. 



The following temperatures were used when studying the changes in optical 

 rotation with time, until optical equilibrium had been obtained : 34.7°, 50°, 68°, 86°, 

 104°, and 140° F. 



The effect of high aging temperatures on the Tyndall phenomenon of pure 

 gelatin-water solutions is now being studied. It is hoped that these data, in con- 

 junction with the optical rotation data, will bring to light a satisfactory explana- 

 tion for the structural changes in a gelatin gel, due to the use of a high (68° F.) 

 initial aging temperature. 



A Study of the Changes that Occur in the Storage of Frozen Sweet 

 Cream. (H. G. Lindquist.) Work has progressed on the preparation of cream 

 for freezing, but no methods thus far have proved satisfactory in studying the 

 changes that occur in the frozen cream. 



