202 MASS. EXPERIMENT STATION BULLETIN 269 



initial crystal condition before hardening is important, otherwise the 

 center of the paclcage Mould be noticeably rougher than the outside. 

 Along with this fact the results of the following experiments may be 

 considered. A pint package of cream from the freezer was placed in 

 the hardening room immediately after drawing, along with another sam- 

 ple enclosed in an insulated jacket in which it is evident that the cooling 

 would be very slow. _The fact that no diiference in texture could be 

 observed as a result of the two methods of hardening again points to 

 the idea that the crystal structure is determined to a very large extent be- 

 fore hardening. 



Influence of Fat on Texture 



In addition to the enriching value of butterfat as earlier mentioned, 

 its effect in improving texture is probably as permanent as any single 

 factor. The padding effect of the fat against the ice crystals is so great 

 that it largely covers up the difference in crystal size. It is possible that 

 the fat actually retards the crystal growth. An example of this action 

 of fat is shown bj' the great difference in the texture of a sherbet frozen 

 by the old brine freezer and in the new continuous freezer, as compared 

 with the far less noticeable difference in texture of a 14 per cent fat ice 

 cream frozen by the two types of freezers. 



Effect of Gelatin on Texture 



A small amount of gelatin is very frequently used to impart greater 

 smoothness to ice cream. The gelatin combines with a portion of fhe 

 water to make it less available to crystal formation and at the same time 

 the gel so formed protects the crystals that do form so as to give greater 

 smoothness. 



In the attempt to improve texture, gelatin was given special study (9). 

 The use of 0.35 per cent of high-strength gelatin (250 Bloom) gave a 

 product of the desired smoothness, while 0.4 per cent gelatin imparted a 

 slightly soggy body to the product. The influence of gelatin is closely 

 associated with aging, inasmuch as mixes containing gelatin are the only 

 ones characterized by a marked increase in viscosity. Starting with the 

 theory that gelatin gel particles are built up from single molecules of 

 gelatin which cause develoj^ment of viscositj' according to the rate of 

 cooling, experiments were conducted which resulted in an explanation 

 for the behavior of gelatin in the aging of ice cream. Briefly, the aging 

 of gelatin in ice cream is the process of the gelatin particle or crystal 

 formation and subsequent gel structure growth. Very rapid cooling 

 of the ice cream mix as normally conducted is unfavorable to crystal 

 growth because the gelatin is in a state of a supercooled melt which does 

 not allow for molecular activity. Thus solidification cannot take place. 

 In this condition of retarded molecular activity there is no heat of fusion 

 liberated. Without this liberation there cannot be an equilibrium between 

 the energy produced and the change of state. However, a slow cooling 

 .iust below the melting point of gelatin results in a subdued molecular 

 activity, permitting the molecules to collide and adhere to form particles 



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