Experimental cookery

Gelation and Stiffening Power o£ Gelatin Gelation is the formation of a gel or solidification of a gelatin solution. In food preparation it is referred to as the setting of the gelatin. The setting point is no clearly defined point. The gelatin solution becomes sirupy, like a thick sugar solution, then gradually thickens to finally form a firm gel. Thus there is no distinct point at which solidification occurs. If samples of solutions are placed in test tubes, the time at which they cease to flow may be taken as the setting point. In larger containers this is not so easy to ascertain, and it is necessary for members of the class to 182 GELATIN compare results and all try to select a definite stiffness as the setting point. Sheppard and Sweet devised an apparatus for determining the setting point. They take the setting point as the point at which a stream of air bubbles ceases to flow through the gelatin solution. The stiffening power and the viscosity of gelatin are affected by several factors. Usually stiffening power and viscosity run parallel, but this is not always true, for gelatins giving the highest viscosity do not always yield the stiffest jellies. Viscosity of gelatin is measured at a temperature of 35 °C. by some workers and at 60 °C. by others. At these temperatures gelatin is a liquid and will flow. Viscosity is measured by the rate of flow under standardized conditions; stiffening power or jelly strength is meas- ured when the gelatin is set. Different brands of gelatin show decided differences in stiffening power when made into gelatin to serve. If two gelatins cost the same per pound, one may be more economical than the other, if equal quantities of the gelatins when combined with the same amounts of sugar, water, and flavor- ing show different stiffening power. Time, concentration, and temperature all affect the gelation process and the stiffness of the resulting jelly. Time of gelation. When concentration and temperature are constant a definite length of time is necessary for gelation to occur. This is character- istic of many colloidal changes. With lessened concentration a longer time is required for gelation. At higher temperatures a longer time is required for the solidification to take place. The firmness of the jelly is also affected by time. Some time may be required after the gelatin solution has cooled to the refrigerator tempera- ture before gelation occurs. The jelly becomes stiffer with longer standing. Gelatins allowed to stand in the refrigerator over night at a temperature of 8° to 10°C. are stiffer than those standing only a short time after gelation has occurred. Clark and Du Bois state that after gelatin has cooled 3 hours at 0°C. little or no further increase in jelly strength occurs. Dahlberg, Carpenter, and Hening found that, for the weak gelatin solu- tions used in ice cream, gel formation requires a long period of time. They allowed 18 hours for gel formation and aging in most of their experiments. However, they found that the gumminess in ice cream due to too much gelatin increased during 4 to 5 weeks' storage of the ice cream. They attributed this to the ''slow rate at which gelatin gels in weak concentra- tions come to a final equilibrium."