Fruit jellies are semisolid, preserved mixtures of fruit juice and sugar. Jelly making is a good way to preserve fruit flavors for enjoyment throughout the year. Fruit jelly is a fairly easy-to-prepare product for the beginning canner and may be made at home without much special equipment.
Substances essential for fruit jelly making are fruit flavor, pectin, sugar, acid and water. A pectin gel or jelly forms when a suitable concentration of pectin, sugar, acid, and water is achieved.
The fruit flavor is provided by the fruit juice. For some fruit jelly, a mixture of different fruit juices is used. The fruit juice may also supply some or all of the pectin and acid. Fruit juice is the source of water in jelly.
Fruits and their extracts obtain their jelly forming ability from a group of substances called pectins. Pectin provides the three dimensional structure which results in a jellied product, which is why it is used in jellies and jams.
Pectin is formed from a parent compound, protopectin, during the ripening of fruit and during the cooking of underripe fruit to extract juice. Fully ripe fruits contain less pectin than partially ripe fruits. For this reason, some jelly recipes specify the use of a portion of underripe fruit.
All fruits contain some pectin. Apples, crabapples, gooseberries, some plums, and highbush cranberries usually contain enough pectin to form a pectin gel. Other fruits, such as strawberries, cherries, or blueberries, contain little pectin and can be used for jelly only if:
- Combined with fruit rich in pectin.
- Or combined with commercial pectin products (these methods are described under short boil jelly).
Test for pectin: If jelly is to be made without added pectin, it is a good idea to test the pectin content of the fruit juice with this easy method. Measure 1 tablespoon of rubbing alcohol into a small glass. Add 1 teaspoon of extracted fruit juice and let stand 2 minutes.
If a good solid mass forms, enough pectin is naturally present in the fruit juice to form a pectin gel. If only a small weak mass forms, there is not enough pectin to form a gel and a commercial pectin should be used in the jelly making. Do not taste this mixture.
A certain level of acidity (below pH 3.5) must be present for a jelly to form. If the fruit juice is not sufficiently acidic, a gel will not form. If too much acid is present, the jelly will lose liquid or weep.
Test of acid: A rough index of the acidity of fruit juice is the juice's tartness. To form a gel, fruit juice should be as tart as a mixture of 1 teaspoon of lemon juice and 3 tablespoons of water. If the fruit juice is not this tart, add 1 tablespoon of lemon juice for each cup of fruit juice.
Commercial pectin products contain organic acids, like fumaric acid, which assure gel formation.
Sugar helps in gel formation, contributes flavor to the jelly, and at the concentration of 55 percent by weight, serves as a preservative. Cane sugar or beet sugar (both sucrose) is the usual source of sugar in jelly or jam. If using special recipes and gelling agents, be sure to follow these methods for best results. See the National Center for Home Food Preservation for reduced sugar spread recipes.