HIGH AGING TEMPERATURES FOR ICE CREAM 5 



aging for 2, 4, and (> hours at 68°. A parallel sample, but aged at 38° served as the 

 control in each case. Bacterial counts were determined by means of the standard 

 plate method. A Leeds and Xorthrup laboratory potentiometer using the quin- 

 hydrone electrode was used in making the hydrogen-ion determinations. The 

 determinations of titratable acidity were made by the Mann's acid test, using 

 N/10 NaOH with phenolphthalein indicator. 



The results of this experiment are given in Tables 1 and 2 and are the average 

 of duplicate determinations. The data indicate that the effect of aging a pas- 

 teurized mix for 2, 4, or 6 hours at 68° F. is of little consequence in commercial 

 ice cream manufacture as far as bacterial count, pH and titratable acidity are 

 concerned. The data on aging at 38° are in agreement with the findings of other 

 investigators. 



Table 1. Effect of Aging at 68° F. ox Bacterial Growth in a 

 Pasteurized Mix 



Time and Bacterial Count Per Gram 



Temperature 



of Aging Trial 1 Trial 2 Trial .3 Trial i Trial ■> Trial 6 



Before Aging 50,000 



Aged 2 hours: 



At 38° F 4.5.000 



At 68° F 52,000 



.Aged 4 hours: 



At .38° F 54,900 



At 68° F 50,500 



.Aged 6 hours: 



At 38° F 42,000 



At 68° F 51,400 



Table 2. Effect of Aging at 68°F. on the pH and Titratable Acidity 

 OF A Pasteurized Mix 



Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 



Time and 



Temperature Per cent pH Per cent pH Per cent pH Per cent Percent 



of Aging Ac'dity .-Xcidity .Acidity Acidity .Acidity 



Before aging 0.182 6.30 180 6.10 0.190 5.9S 0.180 0.200 



.Aged 2 hours: 



At 38° F 180 .190 6.00 .185 .200 



At 68° F 182 6..30 .180 6.25 .190 5.9S .185 .190 



.Aged 4 hours: 



At 38° F 190 6.28 .190 6 00 .190 .195 



At 68° F 1S2 6.33 .180 6.15 .190 5.95 .190 .190 



Aged 6 hours: 



At 38° F 190 6. .30 .180 6 30 .190 5.98 .185 .195 



At 68° F ISO 6.35 .182 6.13 .190 5.98 .185 .200 



The bacteriological results are surprising because it has been taught that even 

 a pasteurized mix must be cooled immediately after homogenization to approx- 

 imately 40° F. in order to avoid increases in bacterial growth. The probable 

 reason for no marked increase in bacterial growth ev^en after holding the mix at 

 68° F. for 6 hours is the natural lag period which follows sudden temperature 

 changes. However, such factors as sugar concentration, surface tension and types 



