PACKAGED ICE CREAM 



203 



and aggregates, or the solid state. Thus the aggregation at the warmer 

 temperature (below 98° F., the melting point of gelatin according to 

 Oakes and Davis (3)), results in particles large enough to impart addi- 

 tional viscosity to the mix as well as apparent viscosity due to the ad- 

 hesion of these particles. From this conception of gel formation it is 

 not difficult to see how mixes of various viscosities may be made simply 

 by controlling the rate of cooling. Experimental evidence of these prin- 

 ciples is shown by cooling portions of skim milk solutions of gelatin from 

 various initial temperatures to 40° F. by holding the portions in a cooler 

 at this temperature for 2}. hours. The viscosity results obtained from 

 such a series are shown in Figure 3. The graph shows that there is a 

 marked increase in viscosity as tlie initial aging temperature is raised 

 to over 80° F. These and all other viscosit.v results obtained were taken 

 after vigorous agitation was given to the material to destroy apparent 

 viscositv structure. 



Fig. 3. Effect of Initial Aging Temperatures on Viscosity of 0.5 Per Cent Gelatin 



in Skim Milk. 



80 foo 120 m 



m 



Various investigators have implied tlmt whatever the apparent vis- 

 cosities might be for a given mix, it could always be reduced to tiie same 

 basic viscosity. This is not the case in view of the above observations. 

 The permanency of these various basic viscosities due to temperature is 

 further shown by their effect on melting ice cream so treated, as illus- 

 trated in the photograph, Figure 4. Therefore, if the occlusion of water 

 by gelatin in the mix cooled in the usual manner is a cause of smoother 

 texture, then the still greater occlusion of water as shown hx the much 

 greater viscosity developed in samples slowly cooled should cause still 

 smoother texture, according to the writer's previous work (9). 



An idea of the imi^rovement obtained by this method may be secured 

 from the following experimental results. A normally aged sample of 

 ice cream was compared with a sample aged by slow cooling from 80° F. 



