198 MASS. EXPERIMENT STATION BULLETIN 269 



range of about 10° F., until the package is sold. The above conditions, 

 howe%er, are coming to be a less serious factor with the general replace- 

 ment of ice and salt by electric refrigeration and the use of dry ice in 

 transportation. Commercial practice has also shown that dry ice trans- 

 portation relieves the necessity of returning unsold goods to the hardening 

 room each day and so eliminates the possibility of one or more heat shocks. 

 As a result of observations made of packaging operations, the conclu- 

 sion was reached that the principal source of poor texture was the condi- 

 tions surrounding the initial crystallization of the ice cream, particularly 

 those affecting the temperature of the package before it is placed in the 

 hardening room. However, in order to give proper emphasis to the im- 

 portance of the initial hardening temperature, it is necessary to modify 

 certain opinions concerning the importance of tiie rate of freezing in 

 the freezer. 



Initial Hardening Temperature Important 



Although it has been regarded that stiffness of mix and the rate of 

 freezing are important, no definite range has been fixed for these factors 

 other than their practical limitations. The effect of brine temperature on 

 the rate of cooling of the mix is shown in Figure 1. It will be noted 

 that the difference of 20° F. in brine temperature caused the mix to cool 

 but twice as fast, or about 1° F. per minute at the point where the first 

 crystallization would take place. A comparison of ice cream frozen with 

 brine of the two temperatures showed that there was no appreciable 

 difference in texture if samples were drawn from the freezer at the same 

 consistency. It is evident that low temperatures were far more significant 

 in shortening the time of freezing than in improving the texture. Even 

 as a means of hastening the process of freezing, the use of extremely low 

 brine temperatures is questionable, for unless the brine is shut off at the 

 exact fraction of a second required, the mix may be so stiff that extra 

 whipping will be necessary to prepare it for drawing. 



The question then remains, what is the most significant factor to be 

 considered? The drawing temperature of ice cream is extremely import- 

 ant as evidenced by the fact that most of the current trade literature 

 emphasizes the significance of a low drawing temperature or a stiff mix 

 in referring to texture. In this investigation numerous series of samples 

 were frozen to varying degrees at the freezer and then were chilled in 

 the hardening room. As the temperature was lowered in the freezer to 

 a rather definite "critical point" below the freezing point of tlie mix, a 

 gradual improvement in the texture of the finished ice cream was noted. 

 Below this "critical point" there was no appreciable improvement. The 

 maximum temperature allowable before hardening was about 25.5° F. 

 for the mix used in this study, which contained 12 per cent fat, 10 per 

 cent serum solids and 15 per cent sugar, with 0.35 per cent of 250 Bloom 

 gelatin. 



The "critical point" temperature is therefore the point at which the 

 maxinmm number of crystals are formed and are consequently small, thus 

 making for a smooth texture. In terms of crystallization this point , 

 appears to be the point of saturation favorable to the greatest number 



