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 (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 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.