From The Food Encyclopedia by Jacques Rolland and Carol Sherman
A gelling agent, stabilizer and thickener sold as a syrup or powder, used in jellies and preserves, which pectin allows to gel because it imparts the requisite level of acidity. Pectin also occurs naturally in some fruits, at its optimal level when the fruit is just ripe; just before and just past maturity, the pectin will fail to set the juice naturally. Fruits with enough natural pectin to form a gel include crab apples, tart apples, quinces, sour blackberries, sour boysenberries, most plums, cranberries, lemons and wild grapes (Eastern Concord variety). Fruits low in pectin, requiring supplementary pectin to set, include cherries, ripe blackberries, grapefruit, grapes, melons and oranges. Fruits always requiring added pectin are peaches, pears, figs, apricots, elderberries, strawberries, raspberries, Western Concord grapes, guavas and pomegranates. Commercial pectins are made from apples or citrus fruits, and are available in both powdered and liquid forms, which are not interchangeable in recipes.
