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Power Requirements for Freezing Ice Cream¹

Kansas Agricultural Experiment Station, Manhattan, Kan.

ABSTRACT

In an attempt to improve the operating efficiency of the 40 quart, direct expansion freezer (Creamery Package) a total of 66 individual batches of ice cream have been made. The rate of freezing, the quality of the finished ice cream, and energy input to the motor were determined in relation to the temperature at which the refrigerant was cut off, the percentage and kind of stabilizer used, the size of motor, and the dasher speed. The results of this study may be summarized as follows :

1. Reduction in the temperature at which the refrigerant was cut off from 25.5 to 24 and 22.5° P. resulted in a decline in the dasher speed and rate of freezing but the energy input to the motor and the total power used in freezing were increased.
   
2. No significant differences were observed in the quality of ice cream when the refrigerant was cut off at 24° P. as compared with 25.5° F.
   
3. Although cutting off the refrigerant at 22.5° P. improved the quality of the ice cream, this temperature was neither practicable nor economical with the equipment used, due to prolonged freezing time and the increased power consumption.
   
4. The use of the proper amount of a suitable stabilizer had a more significant effect on the quality of the ice cream than did a reduction in the drawing temperature within the limits observed (22.7–23.8° F., Table 2). No significant differences were observed in the freezing properties, total power used, or in the quality of the ice cream stabilized with 0.35 per cent of a 250 Bloom strength gelatin as compared with 0.26 per cent Dariloid. The addition of stabilizer to a standard mix increased the freezing time and total power slightly.
   
5. A 5 H.P. motor improved the operating efficiency of the freezer and did not increase the total power consumed. The time required to reach 100 per cent overrun was slightly reduced and the quality of the ice cream was either equal to or superior to that produced with the 3 H.P. motor. In no case was the 5 H.P. motor overloaded, whereas the 3 H.P. motor was seriously overloaded, particularly when a mix containing egg yolk was frozen and the refrigerant cut off at 24° F.
   
6. A marked difference in the energy input to the motor was observed between mixes containing egg yolk and the standard mix, irrespective of the size of motor used. When the 3 H.P. motor was used and the refrigerant was cut off at 24° F. the maximum energy input to the motor amounted to 3.37 kilowatt hours with the standard mix as compared with 4.55 kilowatt hours with the mix containing egg yolk. Similar differences were observed when the 5 H.P. motor was used.
   
7. The use of eggs in the mix shortened the time required to reach 100 per cent overran. A saving of approximately 5.1 minutes per batch resulted when the refrigerant was cut off at 24° F., and a saving of 2.5 minutes per batch when the cut off temperature was 25.5° F.
   
8. Increasing the dasher speed from approximately 170 K.P.M. to 200 E.P.M. resulted in a slight saving in the time required to reach 100 per cent overrun. The energy input to the motor was increased but the total power was not affected appreciably.
   
9. Changing the speed of the dasher had no significant effect on the quality of the ice cream.
   

¹ Contribution No. 112 from the Department of Dairy Husbandry and No. 72 from the Department of Agricultural Engineering.