WASHINGTON — Twenty years ago, you would have been hard-pressed to find enough Christmas beers to fill a six-pack. Today, sighs Larry Robinson of Chevy Chase Wine & Spirits in Washington, "I don't have room for them; the number is increasing astronomically." Every year about this time, his beer inventory swells from 1,000 brands to 1,200. At Brasserie Beck here, Belgian winter beers (strong, dark and spiced) occupy seven of 11 taps.

Now these beers have an entire book devoted to them: "Christmas Beer: The Cheeriest, Tastiest, and Most Unusual Holiday Brews" (Universe Publishing, 2008), by Don Russell. The author, under the nom de plume Joe Sixpack, writes a weekly column for the Philadelphia Daily News.

"When I was a kid, I couldn't wait for Christmas morning. No way could I ever get to sleep," he writes in his book. These days, instead of a toy car or Rock'em Sock'em Robots, he salivates over the newest holiday ales.

The common denominator of Christmas beers is that they have no common denominator. Russell, whose book includes photos and notes on about 150 holiday libations with such names as Hibernation Ale, Old Fezziwig and Belgian Frostbite, remarks that "these seasonal delights can't be defined by color, alcohol content or flavor." Generosity is a hallmark of the season, and many breweries add a little more of what they use during the rest of the year. Rogue Ales' Santa's Private Reserve is its year-round St. Rogue Red with double the Chinook and Centennial hops and the addition of a third, "mystery," hop.

At Christmas, it was once the custom to turn the social order on its head. In a chapter on yuletide festivities, Russell cites the medieval Feast of Fools, in which drunken throngs gathered in churches to watch a fake priest conduct a mock religious ceremony. Feast of Fools is the name of Magic Hat Brewing Co.'s seasonal 12-pack sampler, containing the hoppy amber ale Roxy Rolles and an experimental brew called Odd Notion whose recipe changes with each new batch. The latest Odd Notion is a braggot (a hybrid fermented from malt and honey) spiced with chamomile and aged over toasted oak chips for a delicate floral aroma and crisp finish.

St. Nicholas, Russell writes, is one of several church fathers venerated as a patron saint of brewers, yet 30 states have enacted laws prohibiting any image of Santa Claus on beer labels. Importer Dan Shelton sought help from the ACLU after Connecticut, Maine and New York tried to ban one of his products, a dark, roasty English ale called Santa's Butt Winter Porter. Although the label prominently depicts Santa's (fully clad) posterior, the name is a play on words. A butt is a vessel that holds 162 gallons of beer; "entire butt" is a synonym for porter.

Russell's book contains chapters on Samichlaus (a strong and immensely malty European lager whose name means "Santa Claus" in a Swiss-German dialect) and Anchor Brewing Co.'s Our Special Ale. Anchor owner Fritz Maytag has been releasing a special Christmas ale since 1975; it has been an herb-and-spice beer since 1987. The formula varies each year. The 2008 edition appears to be heavy on nutmeg, with a dollop of a pine or spruce extract.