jelly and jam, gelatinous, sweet food prepared by preserving fresh fruits. Since most fresh fruits contain about 80% water and from 10% to 15% sugar, they are subject to fermentation. They may be preserved by adding sugar and reducing the water content. Almost any fresh fruit can be made into jam by mashing or slicing it fine, adding an approximately equal amount of sugar, and simmering until it reaches the proper concentration or gel at 218° to 222°F; (103°–105°C;). Preserves differ from jam in that the fruit retains its form. For jelly, only those fruits may successfully be used that contain a sufficient amount of pectin pectin, any of a group of white, amorphous, complex carbohydrates that occur in ripe fruits and certain vegetables. Fruits rich in pectin are the peach, apple, currant, and plum. Protopectin, present in unripe fruits, is converted to pectin as the fruit ripens.
..... Click the link for more information. (the chief gelling substance) and acid. Among these are plums, apples, grapes, and quinces and such berries as currants, gooseberries, raspberries, blackberries, and cranberries. Pectin or gelatin gelatin or animal jelly, foodstuff obtained from connective tissue (found in hoofs, bones, tendons, ligaments, and cartilage) of vertebrate animals by the action of boiling water or dilute acid.
..... Click the link for more information. may be added to other fruits, such as peaches and strawberries, but the results do not equal the natural jellies. Jelly is made by extracting the juice of fresh, sound, barely ripe fruit, combining it with sugar, and cooking. Excess heating dissipates the flavor and may hydrolyze the pectin. Too little sugar yields a tough jelly; too much, a sticky one. Too much acid may cause separation of liquid. The manufacture of jams and jellies is now largely commercial.

jelly and jam

Thick preserves made from fruit and sugar. Jelly is semitransparent, consisting of the strained juice of various fruits (occasionally vegetables), singly or in combination, that is sweetened, slowly simmered, and congealed, often with the aid of pectin or gelatin. Jam differs from jelly in its inclusion of fruit pulp or whole fruit; whole-fruit jam is sometimes called preserve. Fruit jellies and jams are eaten on breakfast breads and in sandwiches and accompany the scones and other baked goods of the British tea meal. Vegetable and herb jellies traditionally complement lamb and other meat dishes.