Listen to the article For proper texture, jellied fruit products require the correct combination of fruit, pectin, acid, and sugar. The fruit gives each spread its unique flavor and color. It also supplies the water to dissolve the rest of the ingredients and furnishes some or all of the pectin and acid. Pectins are substances in fruits that form a gel if they are in the right combination with acid and sugar.
All fruits contain some pectin.
Because fully ripened fruit has less pectin, one-fourth of the fruit used in jellies without added pectin should be underipe. Commercially frozen and canned juices may be low in natural pectins and make soft textured spreads. The proper level of acidity is critical to gel formation. For fruits low in acid, add lemon juice or other acid ingredients as directed. Commercial pectin products contain acids which help to ensure a gel.