22 



MASS. EXPERIMENT STATION BULLETIN 287 



at this time also raised the temperature of the mix, which resulted in slower 

 freezing and whipping. The only advantage of adding the fruit after partial 

 freezing of the mix was that slightly larger pieces of fruit were evident in the 

 finished product. 



The idea, now fairly prevalent, that adding fruit early in the freezing process 

 will curdle the mix, is erroneous. Milk prcjteins do not normally curdle at the 

 acidity of fruit ice creams (see Table 10). Furthermore, the rapid agitation 

 inside the freezer at the time of mixing prevents the possibility of coagulation. 



T.-VBLE 10. — Determinations of pH Value in Fruit Ice Creams. 



Flavor 



Number of Low- 

 samples pH 



High 

 pH 



Average Fruit 



pH added 



Per cent 



Vanilla 12 



Raspberry 1 



Cherry 6 



Strawberry: 



1 : 1 pack 9 



2 : 1 pack 6 



3 : 1 pack 9 



Average 24 



The Addition of Flavoring Extracts 



Trials were made to determine whether part of the fruit could be replaced 

 by the addition of strawberry extract. This was found to be impracticable. 

 The majority of strawberry extracts studied did not impart a natural strawberry 

 flavor. Only one extract of the eight studied could be used without actually 

 injuring the flavor of the ice cream. This proved to be so mild in flavor that 

 it was of no particular value. 



About one-third the usual amount of vanilla extract used in the flavoring of 

 vanilla ice cream may be added to strawberry. The vanilla flavor tends to cover 

 off-flavors in the mix. The work indicated, however, that under most conditions 

 the addition of strawberry or vanilla extract to strawberry ice cream was not 

 ju.stifiable. 



Deterioration of Strawberry Ice Cream 



It was observed that strawberry ice cream acquired a storage or rancid 

 flavor in a shorter storage period than vanilla. Wright (22) showed that acidity 

 is a factor in increasing the rate of oxidation of butter fat. Table 10 contains 

 the average pH readings of the different fruit ice creams. The addition of the 

 fruit increased the hydrogen ion concentration of the mix, which would thus 

 increase the rate of oxidation of the fat. By shifting the pH of plain mix to this 

 extent by the addition of pure lactic acid, a more rapid deterioration of the 

 product was observed. 



Tracy concludes (16) that the enzymes in the fruit itself play a part in flavor 

 deterioration. He reported data to show that by heating the strawberries to a 

 temperature of 175° F. for 20 minutes the enzymes were inactivated and the 

 keeping quality of the ice cream was enhanced. This study supports the conclu- 

 sions of Tracy. Dahle (4) concludes that dissolved copper salts play a part in 

 the oxidation of butter fat in strawberry ice cream. 



From the work cited above and the results secured in this study, the con- 

 clusion may be drawn that the more rapid deterioration in flavor of strawberry 



