Experimental cookery

According to Spencer's theory, the precipitation of pectin forms the jelly. Sugar, glycerin, or alcohol may be used as precipitating agents. Spencer states "The successful making of alcohol jellies requires rapidity of motion and practice, otherwise one obtains a precipitate and not a homogeneous jelly." The qualitative aspects of the boundary line between fields of the jelly and the sol shown in Fig. 14 are by Spencer. She states that the quantitative aspects of these boundary lines are meaningless, because the pectin used contained some ash. From this figure it is deduced that jellies with sugar as the precipitating agent are not possible in the neutral region owing to the solubility limit of sugar. Although alkaline jellies are in- teresting theoretically, practically they are of less importance, since they cannot be used as food on account of their flavor. Concentration of pectin required for jelly. The strength of the PECTIN TEST BY ALCOHOL 157 jelly is in proportion to the concentration of the pectin, if other factors re- main the same. Too small a proportion of pectin yields a jelly that is too soft and sirupy ; too great a concentration gives a product that is too firm and hard. However, after a certain amount of pectin has been added any excess re- mains inactive. The concentration of pectin required for a jelly of good con- sistency varies with the proportion of sugar used, the acidity of the juice or solution, the salt content of the particular juice being used, the time, and temperature factors. Good home-made jelly may contain 0.75 to 1.0 per cent of pectin. Commercial jelly, on account of shipping, is somewhat stiffer, averaging about 1.25 per cent of pectin. Pectins from different sources yield characteristic jellies. Olsen states that jellies made from citrus pectins are comparatively friable and Crystallization Limit Alkaline Neutral Acid X-Axis; % Precipitating Agent Fig. 14. — From Spencer, "A qualitative view of the relations of the boundary curves of pectin jelly fields for sugar, glycerine, and alcohol jellies. The alcohol jelly field is the largest, and the sugar jelly field the smallest." J. Physical Chem. 33: 1993. have little elasticity; whereas jellies made from apple pectins are highly elastic, but require and tolerate less acid than citrus pectin jellies similarly prepared. Cranberry pectin tends to yield firm jellies which will not spread readily. Cox states that a better-textured cranberry jelly for spreading pur- poses is obtained if the pectin occurring in the juice is hydrolyzed by adding the enzyme pectinase, available in commercial form under the name Pec- tinol. A slower-setting pectin is then added to the juice. With a rapid- setting pectin gelation may start before the sirup is poured, and the pouring breaks the structure so that a mass of small lumps is formed. Three fairly easy methods of determining the amount of pectin present in fruit juice are available for the housekeeper. One is to cook a small portion of the juice with sugar to see if it will form jelly. Another is to test the juice with alcohol. The third is to test the viscosity of the juice with a jelmeter. Pectin test by alcohol. Alcohol precipitates pectin in a jelly-like mass. By the character of the precipitated pectin an approximate estimate can be made of the amount of pectin in the juice. For the test, 1 tablespoon oi 158 JELLY