Lambic is a sour wheat beer style brewed in and around Brussels. By world standards, lambic brewing is rare and the volume brewed is small. At their best, lambic beers are among the most interesting, complex drinks ever created. The fermentation technique reflects medieval and even ancient times, well before the second half of the 19th century, when Louis Pasteur developed new microbiological understandings and Emil Christian Hansen developed a way to breed pure yeast strains. At one time, all beers were made without knowledge of bacteria and pure yeast cultures, and a certain sourness in taste would have been thought of as typical rather than unusual. With the advances of the 20th century, however, brewing equipment improved and brewing techniques became more sophisticated, especially through revolutions in chemistry and microbiology. Brewing became a more controlled process and beer became a more consistent product that did not sour or spoil as easily. It could be brewed, transported, and stored more reliably, which was of significant commercial benefit to the entire beer trade from producer to retailer. Yet, despite this general trend toward controlled brewing practices, brewing lambic beer has remained an enduring and endearing specialty of Brussels and a few villages in the surrounding region of Payottenland.
Empty champagne bottles in the cellars of the Boon Brewery in Lembeek, Brussels, waiting to be washed. The bottles are filled with lambic, corked, and secured with wire cages to hold the pressure that builds up during the beer’s final fermentation in the bottle. Such bottle conditioning gives the finished beer a crisp, champagne-like effervescence. photograph by denton tillman
At the very heart of lambic is a complex fermentation based on locally and naturally occurring wild yeasts and bacteria. In this, they are analogous to the so-called natural wines that are now reascendant among wine enthusiasts. There are two principal fermentation stages in the lambic process, both involving “wild” or native microorganisms. The first stage produces mostly ethanol and lasts about 3 to 6 months. The second stage produced mostly acids and lasts an average of 12 to 24 months. The nature of all lambic fermentations, often described as spontaneous, is largely determined by the local organisms that inhabit the brewery and its environs. The organisms that find a home in brewery barrels and on timbers and walls over time lend a degree of stability to a particular mix of microbes and thus contribute to the unique character of each brewery’s lambic. Today the lambic style includes beers that are tart and dry, aged and complex, as well as sugar or syrup sweetened and fruity. In an ironic bow to modernity, some are even sweetened with aspartame or saccharin, a practice viewed as distasteful by enthusiasts.
Lambic brewing reflects a synergy with nature and ancient learnings passed on over generations of brewers. Traditionally, lambics are brewed only between October and April, when the prevailing ambient temperature tends to be below 15°C (roughly 60°F). Importantly, the temperature increase over succeeding spring and summer months stimulates fermentation just as yeast and bacterial activities naturally slow down because of the depletion of fermentable sugars.
Lambics have a number of distinctive features when compared with more common beer styles. Whereas malted barley is part of the mash, so is a high proportion of unmalted wheat, sometimes as much as 30%–40%. This mash composition requires an elaborate temperature regimen to gelatinize and convert most of the grain starches into fermentable sugars.
In the brew house, lambics can be mashed by decoction or temperature-programmed infusion.
Lambic fermentations have been an object of intense scientific study, which has resulted in the identification of the many organisms involved. A typical lambic fermentation progresses as a relay of competing organisms that, each in their turn, metabolize the wort’s nutrients and simultaneously change the wort’s chemistry by adding their metabolic byproducts. In this process, as one group of organisms declines, another will start to prosper, grow, and take its turn in changing the ferment. This continues until the last set of microbes has consumed its specific nutrients and made its specific contributions to the beer’s flavor. The final result is the typical lambic taste profile (sour, complex) combined with the specific taste profile from the brewery environment in which it was created.
There are essentially two types of fermentation that turn wort into lambic: an alcohol-producing fermentation and an acid-producing fermentation. The fermentation sequence is divided into four chronologically distinct phases. The first phase occurs at temperatures of 18°C to 20°C (64°F to 68°F) and is driven by such enteric bacteria as Enterobacter cloacae, Enterobacter aerogenes, and Klebsiella aerogenes and such wild yeast strains as Kloeckera apiculata and Saccharomyces globosus. Over the course of a month or so, these microbes cause a mixed-acid fermentation that generates both alcohol and carbon dioxide, as well as acetic, lactic, succinic, and formic acids. This mixture of metabolic products eventually alters the chemistry of the ferment to a point at which the activity of these organisms subsides. As the acidity increases, various Saccharomyces species—such as Saccharomyces cerevisiae, Saccharomyces bayanus, Saccharomyces uvarum, and Saccharomyces inusitatus—begin to prosper and ferment most of the wort’s sugars into ethanol, as well as some higher fusel alcohols, ethyl acetate, and ethyl lactate.
The next fermentation phase involves Pediococcus damnosus, a bacterium that does well at temperatures above 20°C (68°F) and produces lactic acid and diacetyl. This phase may last for 3 to 4 months.
At the final fermentation phase, two Brettanomyces yeasts, Brettanomyces bruxellensis and Brettanomyces lambicus, begin to work. These reside in the ferment at very low concentrations and give some lambics their characteristic “Brett” taste and aroma, which has been memorably described as “horse blanket.” Historically, B bruxellensis was first identified in lambic and appears to be more prevalent in the environs of Brussels, while B lambicus is more prevalent in nearby rural communities. The unique mix of organisms in different locations, therefore, adds to a form of “terroir” and the individual character of different lambic brews. Brettanomyces yeasts ferment any residual extract such as maltotriose and maltotetraose very slowly into small amounts of ethanol and acetic acid. They also synthesize ethyl acetate, ethyl lactate, and tetrahydropyridines—associated with a “mousy” aroma—as well as volatile phenolics—associated with medicinal or barnyard-like aromas—and caprylic and capric acids and esters—associated with “goaty” flavors. Brettanomyces often produce a pellicle, or film, on the surface of the beer in the cask. This reduces the oxidation potential of the cask’s content and thus the risk of acetomonas, which are vinegar bacteria, which would make the beer excessively acetic and vinegarlike.
Typical lambic flavors can be challenging on the palate and, if present in excess or out of balance, can cause flavors undesirable even to the most adventurous drinker. Thus, the lambic brewer walks a fine line between creating sensory delight and sensory offense. Although a touch of lactic tartness, for instance, may create an alluring tangy taste just as it does in good Champagne, an intense sourness may make the beer undrinkable. Likewise, a hint of “goatiness” may add an intriguing complexity to the beer, but too much of it may make the beer taste rancid. This is one reason why many finished lambics are often a blend of several batches, sometimes of several years. Nonetheless, sometimes a lambic batch may actually spoil and has to be discarded because the brew may have been exposed to air postfermentation, perhaps from a damaged cask, stimulating acetomonas bacteria and the overproduction of acetic acid.
Lambic beers have evolved over time into several variations on the same basic theme, and modern brewers are still adapting lambics in different geographies and for different export markets. Next to traditional lambics, which are universally very dry, there are now lambic versions on the market that are sweetened to mask some of the brew’s “wild” character. This development has been the catalyst for a debate in Belgium and even for the formation of a consumer group, which enthusiastically champions the traditional artisanal style.
Unblended lambic is uncarbonated, devoid of foam, sour, and available on tap only at a few locations around Brussels and in the producing villages. It often has a cider-like aroma and taste and is generally poured out of an earthenware pitcher and served in short tumblers. It is a highly complex drink and is not exported. If you look at old Flemish paintings such as Pieter Bruegel’s “Peasant Dance,” the jugs on the tables are typically used for lambic beer.
Bière de mars is a partigyle brew made from the second runnings of a regular lambic mash. It is a “small” lambic of indeterminate kettle gravity.
This version of lambic is relatively low in alcohol and is sweetened with caramelized brown candi sugar. It is often made from a half-and-half blend of regular lambic and bière de mars. Originally faro was a cheaper “working class” version of lambic, but it is now difficult to find.
The most common of the traditional unfruited lambic styles, gueuze (sometimes pronounced “goose,” but more often pronounced “gur-zah”) is a bottle-conditioned blend of young and old lambic—perhaps at a ratio of one-third to two-thirds— usually sold in a corked and wire-caged bottle.
Several popular styles of lambic incorporate whole fruit, fruit pulp, or juice. These are usually young lambics with the fruit sugars creating a secondary fermentation in the cask. Fruit lambics may have a sour and complex character balanced by the fruitiness. Some fruit lambics are a blend of small amounts of traditional lambic and sweetened and pasteurized fruit syrup. Such fruit lambics taste intensely fruity and clean and may be more akin to fruit-flavored beers than complex lambics.
Kriek is a cherry lambic. It is the original and most popular of the fruit lambics. Its color is reddish with hints of amber, and its foam is pink. Traditionally, the cherries for this brew were an extremely sour variety called schaarbeek that were indigenous to only a very limited area around the village of Schaarbeek outside Brussels. Nowadays the sour cherries are also grown in a few other parts of Europe, especially in Poland, as well as in other parts of Belgium, northern France, and Germany. For traditional kriek, the whole cherry fruit is used, fresh after the harvest, when summer temperatures are still high. After the addition of crushed fruit to the beer in the cask, a secondary fermentation starts within a few days. It can be quite vigorous and the cask often overflows with foam. The cask’s bung hole, therefore, may be loosely filled with twigs to prevent cherry pits from floating on the surface and blocking the hole. Interestingly, the twigs are often covered with spider webs, but brewers tend to look kindly upon the spiders because they ensure that no fly or other insect will share in the lambic. Kriek can be matured in the cask for several months as the yeasts consume the cherries. It is traditionally then refermented in the bottle, emerging very dry and fantastically complex.
“Framboise,” which is French for “raspberry,” as well as black currant and peach, are also frequent lambic fruits. But nontraditional fruit, such as cranberries and strawberries, have been pressed into fruit lambic service by modern experimental brewers. Such innovation, although considered rather controversial by many traditionalists, has arguably helped the idiosyncratic lambic family of beers to maintain some level of popularity and the lambic beer style to survive. Sweetened fruit lambics tend to be more drinkable to a larger spectrum of palates and may have eased many consumers into tasting the more demanding, traditional versions.
Shanta Kumara, H. M. C., and H. Verachtert. Identification of lambic superattenuating micro-organisms by the use of selective antibiotics. Journal of the Institute of Brewing 97 (1991): 181–5.