What is Pectin?
Pectin and acid both contribute to jelling. Unripe fruit contains more pectin than overripe fruit, so select unblemished produce that is ripe but still firm and include some unripe fruit as well. Although apples, crab apples, currants, grapes, gooseberries, plums, and cranberries are high in pectin, some cooks prefer to add commercial pectin, which comes in either liquid or powdered form, to assure a perfect jelly. Others combine low-pectin fruits, such as berries, with the juice of high-pectin fruits and add lemon juice to increase the acidity.