200 MASS. EXPERIMENT STATION BULLETIN 269 



of crystal centers, known as the Labile range. Since the "critical point" 

 refers only to the maximum allowable temperature of the product when 

 placed in the hardening room, it is essential to draw the ice cream at a 

 temperature low enough to allow for a slight rise in temperature during 

 handling. The neglect of this point is very probably the cause of poor 

 texture in many instances. Observations in commercial plants as well 

 as in the laboratory showed clearly that when ice cream was allowed to 

 become "soupy" or softer than mix at the "critical point" temperature, 

 the texture was always coarse. 



Observations made by Turnbow (5) are in close agreement with the 

 above conclusions. His results based upon microphotographic observa- 

 tions showed that there was no enlarging of crj'stals in ice cream when 

 initially frozen to about 26° F. or lower for a similar mix. Thus His 

 data correspond to observations made independently in this study. From 

 the results of the investigations at this Station (8) and those of Turnbow, 

 the indication is that the small size of the crystals is primarily dependent 

 upon fairly rapid supercooling to the labile or "critical point" which 

 is the optimum range for spontaneous formation of crj^stal centers. Thus 

 the crystals formed above the "critical point" are large because in the 

 metastable range — above the labile but still below the freezing point — 

 there are but few nuclei formed. Therefore it is highly essential, and 

 here is the answer to our question, that the temperature of a semi-soft 

 ice cream should not rise above the labile or "critical point" because 

 centers or nuclei formed will redissolve, reducing the number of nuclei 

 and thus making for large rather than small crystal formation. 



As would be expected from the foregoing, carelessness in allowing 

 too much time to elapse, with consequent warming of the mix, between 

 the drawing of the package and its entry into the hardening room is 

 a common cause of coarseness. The failure to chill hoppers also con- 

 tributes to M'arming of the product and so is another item influencing 

 texture, as is also the fact that some packaging machines do not function 

 as rapidly as desired with mix of the proper stiffness. It was also ob- 

 served that in filling pans for brick packages, the mix became too soft 

 in filling third portions because of the long time required to empty the 

 freezer. Still another condition favoring the development of coarse ice 

 cream arises whenever the scraper blades are very dull or out of align- 

 ment. Here it was found that the overrun was reached before the mix 

 was sufficiently cooled. 



Those who would have their Dixie cups or similar containers thought 

 of as sample portions of their goods should use extra care in filling these 

 containers by not allowing the mix to become too soft, and so avoid 

 coarse texture. Because of their small size, these cups appear to warm 

 up faster. Here, if the rate of cooling in the hardening room was very 

 significant, the rapid freezing possible because of their size would in turn 

 also cause a smooth texture to result. 



Some have offered the opinion that the paper container at room tem- 

 perature was sufficiently warm in itself to warm the product enough to 

 affect the texture. Attempts to verify this in the laboratory showed that 

 this effect alone was not serious. It is estimated that 400 calories of heat 

 are taken up by filling a pint carton of ice cream from the freezer. This 

 is for a carton at room temperature, weighing about 40 grams with an 



