This category, which also has some crossover with Specialty Beer, is at its basic definition beers that are aged in non-neutral wood. This can to produce an intentional wood-influenced flavor effect (vanillin, caramel, toast), or flavors derived from the alcohol previously aged in the wood if any (bourbon, scotch whisky, sherry), as well as the action of microorganisms living in the wood. A wide variety of base beer styles can benefit from barrel aging, although darker or more alcoholic styles have been popular choices.