Wooden barrels are pot-bellied vessels made of staves. Many sorts of wine and whiskey need to go through the process of aging in oak barrels. Those liquors absorb some components from oak wood, like tannins and vanillin. Naturally, the content of these substances varies in different kinds of oak, giving off different flavors to the beverages. That depends not only on the region in which oak occurs but on the processing of the oak wood as well.