A prune is the dried fruit of certain varieties of the common, or European, plum. Prunes have a thick wrinkled dark-blue skin and a firm pulp. They are eaten fresh or cooked and are used to make prune juice. They are rich in iron and carbohydrates.
Plums grown for use as prunes are raised in the same way as other plums except that the branches are usually not thinned and the trees are allowed to grow larger. The fruit is left to ripen on the tree and either drops naturally or is shaken down. It is picked by hand, put in boxes, and carried to a building where it is dipped in hot water or in a hot lye solution. This helps to make the fruit dry more quickly. The skin may also be pricked to speed up evaporation. The fruit is then spread in a single layer on trays and dried in the sun or by hot-air treatment. Sun drying usually takes from 10 to 14 days. During this time the prunes are turned one or more times to ensure even drying. Hot-air drying requires about 36 hours at temperatures ranging from 135° F. to 180° F. (57° C. to 82° C.). After drying, the prunes are passed through boiling water to clean them. They are then dried briefly, packed, and sold.
California, Idaho, Oregon, Washington, and Michigan are among the major prune-producing states in the United States. The varieties most widely grown are Agen prunes and Italian prunes. Large numbers of prunes are also produced in several European countries.