The first raisins were undoubtedly grapes that had dried naturally on the vine, but more than 3,000 years ago people were picking grapes and laying them in the sun to dry--a process that has remained virtually unchanged. (Today, most raisins are still sun-dried, though some are dried in ovens.) Raisins were a precious trade item in the ancient Near East and also highly valued in ancient Rome (where two jars of raisins could be exchanged for a slave). Spanish missionaries brought them to Mexico and California in the eighteenth century, and nearly all the commercially grown raisins in the United States (and about one-half of the total world supply) now come from the San Joaquin valley of California, where the raisin industry began booming in the 1870s after a heat wave dried the grape crop on the vine.
