Experimental cookery

Another cause for turbidity is discussed by Clayton. At the isoelectric point the gelatin solutions always show more turbidity, a 400 per cent increase in turbidity occurring with a pK variation of 0.03 (pH 4.87 to 4.90). Gelatin stock treated with lime shows greatest turbidity on the acid side of the isoelectric point and, vice versa, those stocks treated with acid possess isoelectric points in the region of pH 7 to 8. Previous history. The temperature to which a gelatin has been pre- viously heated will cause a variation in its viscosity. It may also change its stiffening power. This heating may be due to heating during manufac- ture or to heating for dissolving in the home. The latter is seldom long enough to destroy the jelly strength to any appreciable extent. A gelatin solution that has solidified and then is melted will form a gel in a shorter time for the second or third gelation. LITERATURE CITED AND REFERENCES 187 Agitation and foam formation. Bogue and Alexander both state that agitation or stirring lessens the viscosity of gelatin solutions. This might also affect the jelly strength. Gelatins are often beaten when they have become thick but not firmly set. The beating incorporates air, forming a foam, and the gelatin mixture increases in volume. Bogue states that the ability for gelatin to form a foam is greatest at the isoelectric point. At this point the gelatin particles have a strong tendency to adhere to each other, and this favors foam formation. If the beating is done at the time when the gelatin has set enough to be quite viscid, but has not become brittle, so that the edges break apart, the volume may be increased two or three times that of the original unbeaten gelatin. The lessening of firmness may be partially due to agitation of the gelatin, but part is due to the incorporation of air. The gelatin at this stage is elastic and stretches to surround the air particles. The gelatin that is to be beaten should have the flavoring in larger quantity than for an unbeaten gelatin as the increase in volume causes the flavor to seem less concentrated. If gelatin becomes too firm before the beating is started the gelatin only breaks and air is not incorporated. Whipped cream and beaten egg white are often folded into unbeaten gelatin or into beaten gelatin. LITERATURE CITED AND REFERENCES Alexander, J. Glue and Gelatin. Chemical Catalog Co. (1923). Alexander, J. Colloid Chemistry, Theoretical and Applied, by Selected Interna- tional Contributors. Edited by Alexander. Chemical Catalog Co. (1926). Bancroft, W. D. Applied Colloid Chemistry. McGraw-Hill Co. (1933). Black, J. W. Opacity in Gelatine. Food Technology 1: 162 (1931-32). Bogue, R. H. Chemistry and Technology of Gelatin and Glue. McGraw-Hill Co. (1922). Bogue, R. H. The Evaluation of Gelatin and Glue. Ind. Eng. Chem. 14: 435 (1922). Bogue, R. H. The Theory and Application of Colloidal Behavior. International Chemical Series. McGraw-Hill Co. (1924). Bradford, S. C. The Sol-gel Transformation and the Properties of Jellies. p. 751, Colloid Chemistry, edited by Alexander. Chemical Catalog Co. (1926). Carpenter, D. C, Dahlberg, A. C, and Hening, J. C. Grading Commercial Gelatin and Its Use in the Manufacture of Ice Cream. I. Ind. Eng. Chem.