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Barrels used for aging are typically made of French or American oak, but chestnut and redwood are also used. The presence of vanillin and wood tannins depends on many factors, including the place of origin, how the staves were cut and dried, and the degree of toast applied during manufacture.

The species of oak typically used for American oak production is Quercus alba, a white oak with relatively fast growth, wider grains and lower wood tannins. In France, both Quercus robur and Quercus petraea are considered apt for wine making, but Quercus petraea is considered far superior for its finer grain and richer contribution of aromatic components such as vanillin and its derivatives, methyl-octalactone and tannins. American oak has two to four times as many lactones as French oak.

The 3S,4S isomer of cis-3-methyl-4-octanolide, known as whisky lactone or quercus lactone, is an important ingredient in the aroma of whiskey and other alcoholic beverages aged in oak barrels. It was first identified in whiskey by Suomalainen and Nykänen in 1970. The beverage extracts it from some precursor substances in the oak wood. Humans can detect it at a concentration of 1 μg/L in air.

Phenols within the wood interact to produce vanilla type flavors. Commercially charred oaks are rich in phenolic compounds. Bourbon gains its color and much of its flavor from the caramelized sugars and vanillins in the charred wood of its barrel. Lighter toasting typically imparts more oak flavor and tannins. Heavy toasting dramatically reduces the coconut-note lactones, even in American oak. Toasting raises the concentration of furanic aldehydes in the wood.

White oak has tyloses that give the wood a closed cellular structure, so it resists water and rot; coopers choose it for wine and whiskey barrels because the wood does not leak. Sessile oak, Quercus petraea, is also used for barrel staves. Bulk wines are sometimes flavored more cheaply by soaking in oak chips or added commercial oak flavoring instead of being aged in a barrel.

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