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Pectin

Fruit-juice, which is largely water, holds in solution small quantities of flavoring bodies, sugar, vegetable acids, and, most important for the purposes of jelly making, a body called "pectin." If pectin be present in the fruitjuice, the juice may be made into jelly; if it be absent, it is impossible to transform juice into jelly. The proportion of pectin in different varieties of fruit-juice varies largely. Currants, sour apples, crab apples, and grapes not fully ripe are generously supplied with pectin, while strawberries and cherries are deficient. Also, the quantity of acids present in the fruit has a bearing on the jellying qualities of the juice; sour apples, currants which are notably sour, and unripe grapes are almost sure to yield choice jelly. If failure results with these, it is usually due to the proportion of sugar employed. A given volume of juice contains a certain quantity of pectin in solution, and this quantity of pectin will take care of only a definite proportion of sugar. To have perfect jelly, each and every time, we must know how much pectin is present in the juice and also how much sugar that quantity of pectin can utilize. The presence of pectin in juice can be determined by mixing equal volumes of juice and ethyl alcohol. If pectin is present, a gelatinous mass will appear in the liquid, which may be gathered up with a spoon. By many tests and comparisons one may get a good understanding of how the quantity of pectin varies with the different varieties of fruit-juice; and by making jelly with sugar and juice in different proportions, finally decide on the proportions best adapted to secure the perfect jelly.

With but a superficial knowledge of the real composition of fruit-juice or of why fruit-juice jellied, the housekeepers of long ago worked out the proportions of sugar and juice that would give the best jelly in each case, and the chemist of to-day has really advanced but little farther.