In their constant quest for better-tasting beer, more and more brewers are stealing a page from the spirits playbook by using old whiskey, wine and port barrels to age and flavor their beers. After spending some time in oak, these brews are hitting new levels of complexity that we don't often see in beer.

Putting beer into barrels is technically an old technique--early brewers, of course, had no stainless steel vats in which to store their suds-but this time they're being used for flavor rather than thrift. "Generally speaking, we want the spirit of the spirit to enter the beer," says Scott Vaccaro of New York's Captain Lawrence Brewing Company, whose Nor'Easter, a spicy, heady winter warmer brewed with elderberries, borrows a bit of coconut and vanilla from old Heaven Hill bourbon barrels.

Results vary by beer and by barrel, and availability varies by region, but all these beers can be described as intense. You can find a good selection online at vintagecellar.com and liquidsolutions.biz, or look for these bottles at your local beer shop.

Nor'Easter ($18 for 750 ml) Captain Lawrence Brewing Company ages this spicy winter warmer in different whiskey barrels each year (captainlawrencebrewing.com).

Victoria Ale ($30 for 750 ml) Maine's Allagash Brewing Company makes one of our favorite barrel-aged beers, brewed with grapes and aged in old wine barrels (allagash.com).

Winter's Bourbon Cask Ale ($8 for a 12-pack) Anheuser-Busch brews this easy-to-find beer, so vanilla-sweet from its days in bourbon casks you'd swear it was a cream ale (anheuser-busch.com).

Temptation ($12 for 375 ml) On the West Coast, the Russian River Brewery has barrel-aged beers like this blonde ale, which gains its fruity, oaky flavor and brilliant orange hue from a stint in French oak Chardonnay barrels (russianriverbrewing.com).

Ola Dubh 16-Year Porter ($9 for 12 oz.) Scotland's Harviestoun Brewery ages this beer in single-malt Scotch barrels until it's a smoky, viscous, black-crude brew that should be savored as slowly as the 16-year-old whisky that flavors it. Harviestoun makes 12- and 30-year versions, too (harviestoun.com).