Either form is satisfactory when used in a recipe developed especially for that form. These pectins may be used with any fruit. Many people prefer the added-pectin method for making jellied fruit products because fully ripe fruit can be used, cooking time is shorter and is standardized so that there is no question when the product is done, and the yield from a given amount of fruit is greater. Fruit pectins should be stored in a cool, dry place so they will keep their gel strength. They should not be held over from one year to the next.
Acid is the substance which makes fruit juice tart or sour.
Acid is needed for flavor and for gel formation. The acid content varies in different fruits and is higher in underripe fruits. With low-acid fruits lemon juice or citric acid is commonly added in making jellied products. Also, commercial fruit pectins contain some acid. Sugar helps in gel formation, serves as a preserving agent and contributes to the flavor of the jellied product.