Marmalades often contain citrus fruits and are soft fruit jellies containing small pieces of fruit or peel, evenly suspended in the transparent jelly. Fruit gives each spread its unique flavor and color. It also supplies the water to dissolve the rest of the necessary ingredients and furnishes some or all of the pectin and acid. Good-quality, flavorful fruits make the best jellied products. Pectin is a substance in fruits that forms a gel if it is in the right combination with acid and sugar.
All fruits contain some pectin.
Apples, crab apples, gooseberries, and some plums and grapes usually contain enough natural pectin to form a gel. Other fruits, such as strawberries, cherries and blueberries, contain little pectin and must be combined with other fruits high in pectin or with commercial pectin products to obtain gels. The proper level of acid is critical to gel formation. For fruits low in acid, add lemon juice or other acid ingredients as directed. Commercial pectin products contain acids that help to ensure gelling.