Pectin is a natural fibre found in plant cell walls and most concentrated in the skin of fruits. It is water-soluble and binds with sugar and fruit acid to form a gel. Adding pectin when making jam or jelly also shortens or eliminates the cooking time, resulting in a fresher fruit flavour.
Using pectin, rather than the long boil method, has the additional benefit of yielding up to 50% more jam or jelly from a given amount of fruit. Wine jellies, bottled juice jellies and no-cook jams can only be made by adding pectin. The amount of pectin varies from fruit to fruit & depends on the stage of ripeness and the growing season weather. The riper the fruit, the less pectin.
High pectin / high acid fruits
Crabapples, sour apples, currants, gooseberries, cranberries, lemons, limes, grapes, blackberries, Seville oranges (sweet oranges are low in acid)
Low pectin / low acid fruits
Strawberries, peaches, blueberries, sweet cherries, raspberries, pears, elderberries, overripe fruit.