Experimental cookery

Sheppard and Hudson have reported a new form of gelatin. It is called pressed foam gelatin. It is said to absorb water rapidly and to dissolve rapidly and it is not excessively bulky. Hydrolysis of Collagen Temperature. When collagen is heated with water, gelatin is formed. Bogue states that this occurs at 80° to 90°C. or at higher temperatures. The reaction occurs more rapidly at higher temperatures, but at these tempera- tures more of the gelatin is hydrolyzed to proteoses, peptones, or amino acids. When meat is cooked in hot water the collagen of the connective tissue is converted to gelatin. The gelatin is soluble in the hot water, and as it is dissolved the muscle fibers are separated and fall apart. At tem- peratures below the boiling point of water a longer time is required to hydrolyze the collagen to gelatin. Acids. The addition of a dilute acid hastens the hydrolysis of collagen, but this also increases the hydrolysis of the gelatin to peptones and amino acids. The latter products do not form gels, so that, in the manufacture of gelatin, it is not desirable for the gelatin to contain very much of these products. Softening of connective tissue in cooking meat is brought about in a shorter time by the addition of a small amount of acid. Tomatoes added to a stew will accomplish this purpose. Sometimes vinegar is used. f 180 GELATIN Properties of Gelatin Gelatin Is characterized by forming a solution in water at high tem- peratures and, with high enough concentration, a gel at low temperatures. The dry gelatin has a slightly yellow cast and contains from 10 to 18 per cent of moisture. It swells when put in cold water, the degree of swelling being modified by acids, alkalies, or salts. It dissolves at about 35 °C., and it gels at low temperatures, the exact gelation temperature depending upon the concentration and time of standing. Swelling and Solution The extent to which gelatin swells in water is modified by the surface area, its initial /»H, the presence of or addition of acids, alkalies, and in- organic salts, and its previous history. Bogue states that gelatin tends to absorb water equal to the amount of water it held at the last warming, but not very much over this. Thus the degree of swelling Is modified by the previous history of the sample. This would include treatment during manufacture. Ease o£ hydration of gelatins. The pulverized gelatin swells most rapidly, for It Is finely divided, hence has a greater surface area. Granu- lated gelatin absorbs water quickly, not so rapidly as pulverized, but rapidly enough so that It Is easily used in the home. Sheet gelatin may be thin or rather thick. The thin form Is easily hydrated, but the thick does not hydrate so readily, and therefore requires longer soaking in cold water or a longer period of heating to dissolve. In preparing gelatin dishes the gela- tin Is usually allowed to soak In a small amount of cold water. During this soaking it swells. Bogue suggests that this swelling, by the formation of capillary spaces In the Interior of the gelatin particles. Increases the surface of the gelatin.