Tradition: For centuries beer was fermented, aged, shipped, and served from wood barrels. During the 20th century, most industrialized breweries switched to metal kegs, fermenters, and tanks. In recent decades, American craft brewers began aging base beers in bourbon barrels, and today, brewers the world over use a variety of barrels to age their beers.
Taste: In addition to bourbon barrels, rye whiskey, rum, tequila, and even some wine and sherry barrels are now used in this way. A barrel-aged beer is a fuller-flavored, more complex version of the base beer but is often lower in carbonation. Due to the extra time and expense, barrel-aged beers are typically sold at a premium and are frequently in short supply.