Jam typically contains both the juice and flesh of a fruit or vegetable, although some cookbooks define it as a cooked and jelled puree. The term “jam” refers to a product made of whole fruit cut into pieces or crushed, then heated with water and sugar to activate its pectin before being put into containers:
“Jams are usually made from pulp and juice of one fruit, rather than a combination of several fruits. Berries and other small fruits are most frequently used, though larger fruits such as apricots, peaches, or plums cut into small pieces or crushed are also used for jams. Good jam has a soft even consistency without distinct pieces of fruit, a bright color, a good fruit flavor and a semi-jellied texture that is easy to spread but has no free liquid.” – Berolzheimer R (ed) et al. (1959) Freezer jam is uncooked (or cooked less than 5 minutes), then stored frozen. It is popular in parts of North America for its very fresh taste.
Recipes without added pectin use the natural pectin in the fruit to set. Tart apples, sour blackberries, cranberries, currants, gooseberries, Concord grapes, soft plums, and quinces work well in recipes without added pectin.
Other fruits, such as apricots, blueberries, cherries, peaches, pineapple, rhubarb, and strawberries are low in pectin. In order to set, or gel, they must be combined with one of the higher pectin fruits or used with commercially produced or homemade pectin. Use of added pectin decreases cooking time.