Fruits stored are kept as nearly as possible in a fresh state. Dried fruits have lost water and may contain chemicals used to prevent development of mold; these act also as a bleach. Desiccated fruits have water withdrawn from them by exposure to moisture-free heated air. The rapidity of such drying averts the possibility of mold or bacteria growing.

Canned fruits are cooked. Only such fruits as are palatable cooked should be canned. Bacteria must be kept out after cooking. Sealing, with air excluded, is the household practice. In the laboratory it has been found bacteria do not pass through cotton. Where canned food is not to be shipped it can safely be stopped with cotton. Jams and jellies are covered with paraffin for the same purpose.

Jams and jellies are fruit-juices concentrated by boiling fruit with sugar. Jams contain most of the fruit. Jellies have the cellulose (woody fiber), skins, and seeds strained out. Jellies are congealed, strained fruit-juices that have combined with the sugar added in boiling. The pectin (1%) and acid (1/2 %) make this jellying of fruit-juices possible. Tart fruits usually contain pectin and acid in the proportions needed to cause jellying when the amount of sugar required by each fruit is added. Sweet fruits may lack the acid necessary. This lack may be overcome by using the fruit somewhat green, by adding the acid from grapes (tartaric, used in baking-powder), or by adding some of an acid fruit. The last is the preferable method.

Specific preserving processes are special cookery problems, but the facts stated above give the principles that direct such food-preparation and through which it is understood. Commerce markets some jams and jellies of somewhat artificial composition. (See p. 44).