186 MASS. EXPERIMENT STATION BULLETIN 268 



24 hours, using tlie MacMichael viscosiiiieter. Readings were made with 

 a No. 30 wire and the disc bob. The cup was rotated at the rate of 19.1 

 r.p.m. Readings were taken when the mix temperature in the cup reached 

 68° F. All readings are stated in degrees M. 



The fat globules and clumps were measured using an ocular micro- 

 meter disc standardized with the microscope so adjusted that each of the 

 smallest divisions represented 1.35 microns. One c.c. of the mix was 

 diluted with 99 c.c. of distilled water and mounted as a hanging drop 

 preparation. 



All mixes were frozen in a 40-quart standard motor-driven brine freez- 

 er. The freezer was always pre-cooled by freezing a preliminary batch 

 before any data were recorded. The percentage of overrun and tempera- 

 ture of the ice cream were secured at minute intervals during the freezing 

 process. The brine was shut off at such a time that all batches were 

 frozen to approximately 24° F. A brine held at 0° F. was employed. 



All data represent an average of at least five different trials on differ- 

 ent mixes. Where differences were not marked, a larger number of 

 trials were made. In only one case, which will be mentioned later, 3Td 

 contradictory results occur. 



EXPERIMENTAL RESULTS 



This problem was attacked by first comparing mixes made with sweet 

 cream as the entire source of fat with those differing only in that frozen 

 cream was substituted for sweet. Then the effects of the rate of melting 

 tht frozen cream and of the length of time in storage were established. 

 Following this, an attempt was made to find a way of freezing cream so 

 that its properties in ice cream mix would be more like those of fresh 

 cream. In this part of the work, cream was either homogenized previous 

 to freezing, frozen with 10 per cent sugar, or frozen with 0.5 per cent gela- 

 tin. Plain pasteurized frozen cream was used for the control batches. 



The data in Table 1 are a summary of all the viscosity determinations 

 and microscopic measurements of the fat phases. Figures 1, 3, 4, and 5 

 were compiled from freezing data collected from the same mixes as 

 represented in Table 1. Therefore, correlations may be made between 

 the table and figures. It should be realized that all observations were 

 made on ice cream mixes of the same composition. Where gelatin or 

 sugar was added to cream before freezing, this was taken into account 

 and proper adjustments were made in the amounts of these ingredients 

 v/hen the mixes were prepared. 



The Physical Properties of Frozen Cream Mixes 



Table 1 and Figure 1 show the marked differences between mixes made 

 from sweet and frozen cream. The frozen cream mixes averaged more 

 than twice as viscous, according to the method used for comparison. 

 Both the individual fat globules and the clumps were smaller in mixes 

 made from sweet cream. A marked difference in freezing time was 

 found. The sweet cream mixes could be drawn at 95 per cent overrun, 

 and at a drawing temperatures of 24° F., in approximately two and one- 

 fourth minutes less time than frozen cream mixes. 



9 



