Tobacco is used occasionally as a food flavoring, and its curing resembles the making of tea. The leaves of the notorious North American native Nicotiana tabacum, a relative of the potato and tomato, are harvested when they begin to turn yellow and develop resinous secretions, then either sun-cured or fermented in heaps for several weeks, and dried by contact with hot metal. These treatments develop a complex aroma with woody, leathery, earthy, and spicy notes, and these are sometimes augmented with the addition of various essential oils (vanilla, cinnamon, clove, rose, and others). Tobacco leaves contain astringent tannins and bitter nicotine, so they are usually infused only lightly into sauces, syrups, and creams. Sometimes whole leaves are used as a disposable wrapper to flavor a food during cooking.