Raisin dehydration in heated air dryers was first devised in the early part of the twentieth century as a means of salvaging rain-damaged raisins. It was also used for a short period to preserve wine grapes during the Prohibition era after ratification of the Eighteenth Amendment. In 1925 the light colored golden bleached raisin was developed, and it required dehydration. Annual production of this new product was about 25,000 tons until World War II. During the war, dehydration was used extensively to ensure a stable supply of product. Many of the earliest dehydrators had no fans and used natural draft to slowly move air past fruit placed on a slotted floor or through fruit placed on trays. In the early 1920s commercial dehydrator firms began marketing a number of types of forced-air dehydrators and these quickly became the industry standard. The main differences between the designs were the location of the air re circulation duct, the type of heating system, and the type of fan, but they operated in the same general fashion as the truck-in-tunnel dehydrators now in use.