Prunes are a variety of plum, though most people take the word prune to mean a dried fruit. Nonetheless, you can buy fresh prunes (the best fresh-eating types are sold as Italian plums or prune plums). The vast majority of these plums are sold dried, because they have characteristics that make them better suited to drying than other types of plums. They generally have firmer flesh, more sugar, and a higher acid content--traits that make it possible for the fruits to be dried with their pits intact without fermenting. In addition, prune plums usually are freestone, while many other plum varieties (though not all) are clingstone. The most common variety of plum used for prunes is California French, also known as d'Agen. The variety is a descendant of the first prune plums brought to the United States from France by Louis Pellier, who started a nursery in California in the 1850s. Today about 70% of the world's prune supply, and almost 100% of domestic prunes, come from California. The transition from plum to prune is a carefully controlled process. The plums are allowed to mature on the tree until they are fully ripe and have developed their maximum sweetness. Then they are mechanically harvested and dried for 15 to 24 hours under closely monitored conditions of temperature and humidity. Because the plums lose so much water, about three to four pounds of the fruit are needed to produce a pound of prunes. After drying, the plums are sorted by size and then stored to await packing, at which point they are given a hot-water bath to moisturize them. As with other dried fruits, the drying process concentrates the nutrients in prunes. First and foremost, they are a high-fiber food: Ounce for ounce, prunes contain more fiber than dried beans and most other fruits and vegetables. Over half of this fiber is of the soluble type that studies have linked to lowered blood-cholesterol levels. Prunes are also rich in beta-carotene and are a good source of B vitamins, nonheme iron, and potassium. The drying process concentrates the sugar content as well, which makes whole or pitted prunes a good snacking food. (Of course, the calorie count also increases--prunes contain more than four times the calories, by weight, that plums do.) Beware, though, of "health snacks," such as trail mixes and granola bars, that emphasize prunes as an ingredient: Frequently, the prunes are mixed in with high-fat ingredients, such as nuts and coconut chips. Diced prunes, prune paste, and prune bits are used in prepared foods, particularly baked goods, to enhance taste and texture (though the quantity may not be sufficient to offer much nutritional value).