The process of maturing a spirit or wine inside an oak barrel so that it slowly extracts tannins, vanillin, and other wood compounds, unlike bottle aging, which involves no wood contact. It is central to producing whiskey, bourbon, and cognac, as well as many red and some white wines, with the species of oak (American, French, or Hungarian), the degree of toasting, and the length of aging all shaping the final flavor; longer, more heavily charred aging tends to add more caramel, vanilla, and smoke character. The practice is occasionally extended to non-alcoholic foods, such as maturing cheese or curing meat in a used barrel.