Two years ago, Allagash Brewing Company’s Rob Tod was bottling his Belgian Tripel ale, when he faced a brewer’s darkest nightmare: He was short on bottles, which meant he’d—the horror!—need to dump his beer.

To prevent this catastrophe, the Portland, Maine brewer poured the Tripel, a sweet-tasting, golden-yellow brew, into a couple of empty Jim Beam oak casks hanging around the brewery. When he tasted the Tripel a couple of days later, “it was totally transformed,” Tod says. “We made a new beer.”

The serendipitous brew became Allagash’s bourbon-barrel-aged Curieux, one of the suds spearheading a resurgence of limited-edition, cask-aged beer. From the chardonnay-barreled Temptation blond ale at Santa Rosa, California’s Russian River Brewing Company, which won a gold medal at this year’s World Beer Cup, an international competition for commercial breweries, to the burgundy-barreled La Folie sour ale from Fort Collins, Colorado’s New Belgium Brewing Company, mad-scientist American microbrewers—and even Anheuser-Busch, with its barrel-aged Michelob Celebrate Vanilla Oak reinventing a European tradition.

Barrel aging mellows and transforms beer, providing lush, woodsy notes and the flavor of the cask’s previous contents, which range from red wine to bourbon to port. Until the late 19th century, beers in both America and Europe were seasoned in oak casks. Their earthy flavors leached into the mixture, creating unique concoctions. It was—and remains—a time- and labor-intensive process. When brewers began mass production, using stainless steel vats, it ushered in a dark century of “getting beers cleaned up,” says Greg Hall, head brewer of Chicago’s Goose Island Beer Company, which hosts the annual Festival of Wood and Barrel-Aged Beer. “And now we’re seeing the beer world go full circle.”

While the brewing methods of lambics (a pleasingly sour, low-fizz brew aged in barrels) have been unchanged for centuries, “the boundaries of what brewers can create with barrel-aged beers are limitless,” says Ray Daniels, author and director of craft-beer marketing for the Brewers Association. American brewers have used aging as a way to experiment. “It’s pretty easy to throw something in a barrel and see what happens six months later,” says Daniels.

Smuttynose Brewing Company, in Portsmouth, New Hampshire, recently released the S’Muttonator Doppelbock lager, which spent two years in Jack Daniels barrels (by law, bourbon and whiskey distillers can use casks only once). The result was a belly-warming potion with whiskey notes, with a smoothness belying its nearly double-digit alcohol content. “I can make an ale in two weeks, but there’s something special about waiting years for the finished product,” says Dave Yarrington, Smuttynose’s head brewer.

Barrel aging often makes potent beers more palatable, though brewers are often more interested in unusual flavors. Barrel seasoning works for lager, pilsners, and stouts alike, though it’s sometimes tricky marrying beer styles to barrels. While thick, dark stout would work with bourbon-infused oak, a thin pilsner would be overpowered, says Jason Alström. He’s cofounder (with brother Todd) of the influential website BeerAdvocate, as well as organizer of the Extreme Beer Fest, which often features barreled brews.

Alström recommends Paso Robles, California’s Firestone Walker 10, a rich blend of ten beers seasoned in oak casks. He also suggests trying Dexter, Michigan’s Jolly Pumpkin Artisan Ales, which exclusively barrel-ages. Standouts include the Oro de Calabaza golden ale (gold-medal winner at 2004’s Great American Beer Festival) and the Perseguidor sour, which is cellared in bottles for six months before it’s sold.

Battles, though, are being waged over Goose Island’s Bourbon County Stout, which received a gold medal at 2006’s World Beer Cup. “The demand for our barrel beer is out of control; we’ve got distributors fighting over cases,” Hall says. “I guess we just have to make more next year.”

To buy these beers, visit the brewers’ websites, or and Liquid Solutions. Note: Beers are subject to availability.

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