A glossary of Belgian beer.

An abbey-style beer brewed by a commercial brewery, often under license to a monastery or evoking monastic tradition, but not a true Trappist beer.

Alcohol by volume, the percentage of alcohol in the beer. Belgian ales range widely, from sub-4 percent table beers to quadrupels above 11 percent.

The sharp, vinegary sourness produced when oxygen reaches the beer. A trace adds lift and complexity, particularly in Flanders reds; too much is a flaw and tastes like salad dressing.

Hops deliberately stored for one to three years until they lose most of their bitterness and aroma, keeping only their preservative power. Essential to lambic, where fresh hop character would fight the wild fermentation.

The ATP label, a hexagonal logo certifying that a beer is brewed at a Trappist abbey or in its immediate vicinity, under strict conditions. Only a handful of breweries qualify, and the mark is awarded per product rather than to a monastery as a whole.

A broad catch-all for amber to brown Belgian ales of moderate strength, malty and lightly spicy without the weight of a dubbel or the sweetness of an abbey ale. More a family than a strict style.

Fruit beer built on a normal ale base rather than on lambic, which is the crucial difference. Usually sweeter, rounder and less acidic than a kriek or framboise, and far more common in export markets.

A modern hybrid, taking the hop load of an American IPA and fermenting it with expressive Belgian yeast, so the citrus and pine sit alongside pepper and fruit esters. A recent arrival, not a traditional style.

The pattern of foam that clings to the inside of the glass as you drink, a sign of good head retention and a clean glass.

A copper-coloured, everyday ale of around 5 percent, balancing biscuit malt with gentle hop bitterness. Belgium's answer to the English bitter, brewed for drinking rather than contemplating.

A pale, potent, effervescent ale of around 8 to 9 percent, fruity and dangerously drinkable. Duvel set the template.

The art of marrying lambics or batches of different ages to build a balanced beer, the heart of gueuze making and the craft of the geuzesteker (blender).

A second fermentation that happens inside the sealed bottle, with added yeast and sugar producing natural carbonation and allowing the beer to mature and age.

A wild yeast (often shortened to Brett) that gives lambic, Orval and many sours their earthy, funky, hay-like and tart character, developing over months in the bottle.

Belgian rock or syrup sugar added to the boil to lift alcohol without adding body, and, in dark forms, to deepen color and add notes of caramel and dark fruit.

Aging strong, bottle-conditioned Belgian beers over months or years, softening their edges and developing deeper, sherry-like and dried-fruit notes.

A wide, heavy, stemmed goblet used for Trappist and abbey ales, opening up aroma and supporting a thick head. Many abbeys etch the glass bottom to spark carbonation.

A wide, shallow open vessel (koelschip in Flemish) where hot wort is left to cool overnight, exposing it to the wild airborne yeasts that start spontaneous fermentation.

A fermentation by-product tasting of butter or butterscotch, with a slick mouthfeel. Usually a sign of rushed or unhealthy fermentation, and out of place in Belgian styles.

A clean, crisp end with little residual sweetness, characteristic of well-attenuated Belgian ales like saison and tripel.

A dark, malty abbey ale of about 6 to 8 percent, rich with notes of dried fruit, caramel and spice.

Flemish for single, a modest table beer brewed for the monks' own daily use, lighter than the dubbel and tripel sold to the public. Also called a patersbier.

The traditional Belgian café: small, wood-panelled, unhurried, and built around conversation rather than volume. The word carries a whole drinking culture, and the best beer bars still aspire to it.

Fruity aroma compounds produced by warm ale fermentation, giving Belgian beers notes of banana, pear, apple and stone fruit.

A broad family of rustic, often dry rural ales, including saison, brewed historically on farms with whatever was at hand.

A traditional low-strength lambic sweetened with candi sugar, historically the everyday table beer of Brussels.

A tart, fruity, wine-like ale from West Flanders, aged for up to two years in large oak foeders. Rodenbach is the benchmark.

A tall, narrow glass that shows off the sparkle and fine bead of gueuze and other effervescent lambics.

A large upright oak vat, sometimes holding tens of thousands of liters, used to age and sour beers like Flanders red over months or years.

A lambic refermented with raspberries, the fruit sugars feeding a second fermentation. Bone dry in the traditional versions and sweetened in the commercial ones, which is why two bottles labelled framboise can taste nothing alike.

A lambic refermented with fruit, such as cherries (kriek) or raspberries (framboise), the fruit feeding a second fermentation.

The earthy, barnyard, leathery aroma imparted by Brettanomyces and wild fermentation, prized in lambic and aged sours.

A house that buys lambic wort or young lambic from brewers, ages it in its own casks and blends the result, without brewing at all. Hanssens is the classic surviving example. The Dutch term is geuzestekerij.

A blendery that buys lambic from breweries and ages and blends it into gueuze, rather than brewing its own wort. 3 Fonteinen and Tilquin began this way.

Borrowed from wine, and not a protected term in beer. On a Belgian label it usually signals a brewery's stronger, longer-aged or more heavily blended version of a beer, as with Rodenbach Grand Cru. Treat it as a claim of ambition rather than a guarantee.

The lighter, wheat-leaning cousin of saison, historically brewed for Hainaut miners rather than farm workers. Low in strength, dry and refreshing. Nearly extinct for decades and now quietly reviving.

A sparkling, dry, tart beer made by blending young and old lambics, then refermenting in the bottle. Often called the Champagne of Belgium.

The High Council for Artisanal Lambic Beers, the association of oude geuze producers of the Pajottenland and Senne valley, formed to promote and protect traditional lambic. Organiser of the Toer de Geuze.

A lambic or sour ale macerated with whole cherries (kriek is Flemish for cherry), yielding a tart, fruity, often dry beer.

The soft, clean sourness of yoghurt or fresh cheese, produced by Lactobacillus and Pediococcus. The dominant acidity in a well-made gueuze, and the pleasant kind.

A souring bacterium that produces lactic acid, giving a clean, yoghurt-like tartness. One of the three organisms behind Belgian sour beer, alongside Brettanomyces and Pediococcus.

A wheat beer from the Senne valley around Brussels, fermented spontaneously by wild yeast and bacteria rather than pitched yeast. Aged in oak, it is the base for gueuze, kriek and faro.

Fermentation using a blend of yeast and souring bacteria such as Lactobacillus and Pediococcus, central to Flanders reds and oud bruins.

Traditional European aroma hops prized for subtlety. In lambic, hops are deliberately aged until stale, used for preservation rather than bitterness or aroma.

An East Flanders brown ale, sweet-and-sour and lightly tart, blended from young and aged batches. Liefmans is the classic example.

What air does to beer over time. In a delicate or hoppy beer it is a fault, flattening aroma and turning it papery or like wet cardboard. In a strong dark ale it is often desirable, producing the sherry, port and dried-fruit notes that reward cellaring.

The rural region southwest of Brussels, part of the Senne valley, whose terroir of wild airborne yeasts makes traditional lambic possible.

Literally fathers' beer: the low-strength ale a monastery brews for the monks' own table rather than for sale. Usually the lightest thing the abbey makes, and often only available at the gate.

A souring bacterium that produces lactic acid and, in its early stages, a slimy texture brewers call ropiness. Brettanomyces later cleans this up, which is one reason lambic needs years rather than months.

Spicy, clove-like aroma compounds from Belgian yeast, a signature of styles like witbier, saison and tripel.

A very strong, dark abbey ale of roughly 10 percent or more, layered with dark fruit, malt and warming alcohol. Also called a Belgian Dark Strong Ale.

A renewed fermentation triggered after the main one, whether in the bottle, keg or with added fruit, deepening flavor and carbonation.

A dry, spicy, highly carbonated farmhouse ale from Wallonia, originally brewed in winter to refresh seasonal farm workers (saisonniers) through summer.

The river valley around Brussels, the only place where the specific wild microflora needed for authentic lambic occur naturally.

A historic Belgian pale ale style created in the years around 1900 as a homegrown answer to imported pilsner and English ale. Amber, lightly sweet and modest in strength. The name survives on labels more often than the style is discussed.

Fermentation by wild yeast and bacteria carried on the air, rather than a pitched yeast strain. The defining method of lambic, possible only in and around the Senne valley.

Table beer of 1 to 3 percent, once served at Belgian family meals and even in school canteens. Brewed for refreshment and nutrition rather than effect, and largely displaced by soft drinks.

A biennial open day, run by HORAL since 1997, when the lambic breweries and blenderies of the Pajottenland open their doors together. The one weekend to see the whole tradition working at once.

Warm fermentation with ale yeast that rises to the surface, used for nearly all classic Belgian ales and producing fruity, spicy character.

Beer brewed within the monastery walls or in the immediate vicinity of the abbey, under the supervision of the community, with profits supporting it. A designation of origin, not a style.

A strong, golden, deceptively smooth ale of around 8 to 9.5 percent, defined by Westmalle in the 1930s. Spicy and bright, with a dry finish.

A stemmed glass that curves out then in, capturing aroma and holding a dense head. Favored for strong golden ales and many Belgian ales.

A complex traditional mashing method used for lambic, leaving unconverted starches that feed the wild microbes through a long fermentation.

A pale, cloudy wheat beer spiced with coriander and orange peel. The style nearly died out before Pierre Celis revived it in Hoegaarden in 1966.

The sweet, unfermented liquid drawn off the mash, before yeast turns it into beer. Traditional blenders such as Hanssens buy wort from lambic brewers rather than brewing any themselves.

Cantillon's annual one-off release, poured on a single coordinated day at selected bars worldwide. Zwanze is Brussels dialect for a joke or a bit of mischief, which is roughly the spirit of it.