638 MILK 



The freezer should be stopped at 27 to 28 F., when the cream 

 mixture has a consistency of condensed milk. The fat has no 

 influence on the freezing-point, as it solidifies at a much higher 

 temperature, but when a cream rich in fat is used the product is 

 firmer than one made of lean cream. Flour and starches also do 

 not affect the freezing-point, while eggs and gelatin depress the 

 freezing, although so slightly that the effect is of no practical 

 significance. Sugar, on the other hand, depresses the freezing- 

 point materially. 



If ice-cream were frozen without agitation, the different con- 

 stituents, having different freezing-points, would separate. This 

 separation is prevented by the whipping, although there is a be- 

 lief among some ice-cream manufacturers that fat is "lost" during 

 the freezing process. Figures published by Wyman seem to 

 bear out this belief, since he found differences varying from 8 to 

 28 per cent, fat in samples taken from the freezer at different 

 periods, while the original mixture contained 18 per cent. fat. 

 In an investigation made by Gordon and the writer the differences 

 were so slight as to range within experimental error. It is true 

 that in a preliminary series of tests some differences in fat content 

 were found, but this was due to imperfect technic. During the 

 ripening process it 'appeared that there was a slight movement 

 of fat toward the center and top of the can, as shown by the fol- 

 lowing figures: 



AVERAGES OF PERCENTAGE OF FAT FROM EIGHT CANS OF ICE-CREAM 



Series number 



1-3. 4-8. 1-8. 



Kind of sample. Per cent. fat. Per cent. fat. Per cent. fat. 



Bottom at edge 8.27 7.98 8.09 



Center of bottom 8.23 8.60 8.46 



Halfway to center of bottom 8.40 8.98 8.76 



Edge at top...' 8.73 9.00 8.80 



Halfway to center at top 8.80 9.20 9.05 



Center at top 8.43 9.42 9.05 



Average 8.48 8.86 8.70 



Washburn could find no difference in fat content between the 

 portions taken at the top, middle, and bottom of the can which 

 was held solidly frozen for a week, but he did find considerable 

 differences in cream which had softened, as the following figures 

 show : 



FAT CONTENT OF DIFFERENT PORTIONS OF SOFTENED ICE-CREAM (WASHBURN) 



. Sample No. r 



Sample from 1234 



Top 28 22 10 12 



Middle 15 14 8 8 



Bottom 5.5 8 6 4 



These figures show a very material movement of the fat, and 

 while the fat rises, the heavier substances such as fruit, syrups, 



