Lambic beer is one of the oldest styles still being made. There are perhaps a dozen Belgian breweries still making traditional Lambic, and all of them are clustered in and around Brussels. Lambic is very closely associated with the Pajottenland region of Belgium, an area that is southwest of Brussels. The name Lambic is probably derived from a town in the region that has traditional associations with Lambic brewing; the town of Lambeek, or "Lime beck," which means lime stream or creek. Lambic is essentially a wheat beer, with malted barley and unmalted wheat; the hops are there largely as a preservative, rather than for flavor.

There are two aspects of the traditional brewing process that make Lambic unique. First, unlike most traditional ales or lagers. Lambic is fermented by leaving the beer wort in large open vats where it is deliberately exposed to "wild" yeasts and microorganisms in the air; it is this exposure that produces the characteristic "sour" taste (this is a direct result of lactic-acid bacteria) and the sort of hay-barn scent associated with traditional Lambic is a characteristic of Brettanomyces yeasts. The requirement that the yeast be naturally occurring "wild" yeast means that the production is severely limited by seasonal weather. The other unusual aspect of Lambic production is that the beer is, when made the traditional way, carefully aged in wooden casks previously used to age wine or sherry for two or more years. It is this step that some modern brewers skip or cut short, which is a pity; Lambics improve with age, and, if made properly, once bottled will last twenty or thirty years, much like fine red wines. Traditionally made Lambic is verifiably a medieval style of beer, one with historic records that refer to the medieval brewing method, pretty much the same method used today.

There are several styles of Lambic beer. Some are made by carefully selecting and blending several beers, and then aging the the blend. Traditional "pure" Lambic is unblended, unfiltered (and thus cloudy), and uncarbonated, with a markedly sour, even acidic taste, sometimes compared to very dry cider. Cantillon Brasserie, probably the best known of the traditional Brussels Lambic brewers, is very closely associated with this style. Their Cantillon Grand Cru Bruocsella is a traditional Lambic, and it is exported, though hard to find.

Faro is traditionally a deliberately sweetened beer. Traditionally unrefined sugar was added just before serving to a beer made by blending lambic with a lighter, lower alcohol and freshly brewed "young beer," called meertsbier. It was an effort to make an inexpensive everyday beer. Now Faro is still made by adding sugar to lambic, but it's neither light nor inexpensive. It is also bottled and heat pasteurized to stop fermentation. I notice that some of the Belgian Faro labels (it's currently produced by Cantillon, Boon and Lindemans) look very much as if they are meant to appeal to women.

Gueuze is made by combining a carefully selected mixture of one year old young one-year lambic and older two and three-year old lambics is produced and then bottled. After bottling, Gueuze undergoes a secondary fermentation, producing carbon dioxide, because the younger Lambic are still fermenting. Gueuze will keep for several years in the bottle.

In addition, there are a number of "fruit" Lambics; these are made by adding fruit flavorings to the Lambic base. Casis is made with black currents, Framboise with raspberries (and hence the traditional deep ruby red color, and pronounced raspberry scent). Kriek is typically flavored with sour cherry. Muscat is made with black grapes, and tends to be purplish, even reminiscent of wine in flavor. Peche has peach flavoring added. The thing to be careful of, and that very much confused me, is that a beer may be labeled "Framboise," for instance, and actually not be a Lambic; it is instead a beer (usually a fairly weak, flavorless beer) that has been flavored with corn syrup flavored with fruit juice or essence just before bottling. (I'm not talking about craft brews here, but the larger commercial "fruity" beers). In traditional Lambic brewing, the "fruit" Lambics were made by adding whole fruits to the beer, letting them steep, then removing the fruit before bottling. The added fruit brings natural sugars with it; this essentially jump starts the yeast into a second fermentation.

There aren't that many Belgian Lambic brewers who export; Brasserie Cantillon, perhaps the most traditional of them all, exports a small quantity to the U.S. through their distributor Shelton Brothers. If you have a sharp eye, you might spot bottles of Lambic of various sorts, particularly bottles from Cantillon Brasserie or Belgian brewer Drie Fonteinen's Lambic at a local Whole Foods, Trader Joe's, co-op, or beer specialty store. It likely will be a large bottle, 750 ml, but it's a case of buying it when you see it; it likely won't be there next time. For more about Lambic:  read "Lambics: Beers Gone Wild" New York Times and Peter Van Osta's The Lambic Beers I'm going to leave you with this fabulous Wall Street Journal video about Brasserie Cantillon's process for making Lambic.