Basically a raisin is a dried grape made from sweet globes of the European type (Vitis vinifera), grown in warm sunny climes. Once upon a time they would have been dried naturally on or off the vine, but these days are often dehydrated artifically.
Raisins are an ancient food, easily made, preserved, and shipped, and they were an important early trade item throughout the Mediterranean region. Today California and Australia are the major producers of raisins. In California the most commonly used grapes are Thompson seedless, a medium-sized green grape which can yield dark or golden raisins. Dark raisins are sun-dried for several weeks, which makes them shrivel and darken; golden raisins are treated with sulphur dioxide to prevent colour change and dried artifically to give a moister, plumper product. Golden raisins are often called sultanas in America. Raisins are also often made from muscat grapes: these ones are sweet, dark, musky, and sticky. Zante grapes are used to make tiny seedless dried currants, which are more often used in cooking than eaten raw. Be aware that many grapes are bleached and dipped in oil to improve their appearance.
Raisins are naturally high in sugar and vitamins A and B, as well as iron. They can be eaten as is or added to cooked and raw dishes; they are especially popular in baked goods. They should be kept tightly sealed in a jar or plastic bag; for storage of longer than a year, refrigerate.