There are four mail methods of curing. Air-cures tobacco is hung in unheated, ventilated barns until the tobacco dries and the tobacco leaf becomes a light to medium brown color. Flue-cured tobacco is made when heat is introduced into a barn through pipes from a furnace outside. The leaves are heated until they turn yellow: Sun-cured tobacco leaves are hung out on racks and exposed to the sun's rays. The direct heat turns the leaves a yellow to orange color. For fire curing, wood is burnt under the tobacco leaves, which dries the tobacco and produces a smoky fragrance.