Duvel, Belgium’s iconic and elegant golden strong ale, is pale, dry, highly carbonated, and it boasts a distinctive fermentation profile. What are the stories, ingredients, and processes behind the archetype?

Breandán Kearney Apr 11, 2022 - 15 min read

Photo: Matt Graves/mgravesphoto.com

Belgian golden strong ale is a style of simple construction that requires exacting execution. Its most famous commercial example—Duvel, from the Duvel Moortgat brewery south of Antwerp—is a mainstay on the beer menus of Belgian cafés, its branding instantly recognizable: the red gothic calligraphy on white background with large letter “D.” Its voluptuous ballon glass was one of the first tulips to appear in Belgium, sharing functional and aesthetic elements with the Burgundy sampler. The beer marries the fermentation flavors and malt character of a Belgian tripel with the clean, dry drinkability of a German pilsner. Before Duvel, there was no such thing as Belgian golden strong ale.

Brouwerij Moortgat originally launched Duvel in 1923 under the name Victory Ale. Some stories suggest that its name derived from the initials of the brothers who ran the brewery: “V” for Victor and “A” for Albert. In reality, its name was most likely influenced by the end of the First World War, much like other “Liberation Ales.” According to Duvel Moortgat, the beer took its current name during a tasting at the brewery years later. That’s when a local shoemaker named Van De Wouwer exclaimed that the beer was “nen echten Duvel”—in the region’s dialect, “a real Devil.”

Duvel’s ingredients are fairly simple. Its fermentables are straightforward: they come from just one malt—pilsner—and the addition of highly fermentable liquid dextrose, reaching a famously sneaky 8.5 percent ABV. Likewise, its hops are straightforward: It’s hopped with two varieties—herbal, spicy Czech Saaz and earthy, peppery Styrian Goldings from Slovenia. The brewers deploy these varieties at various stages of the boil, targeting 32 IBUs. It is Duvel’s yeast that seems to be the element surrounded with the most mystery.

The origin story of Duvel’s yeast is represented in Duvel Moortgat’s marketing literature as an odyssey, unique and epic. Unlike other family breweries that may have secured strains from yeast banks at Belgian universities, Duvel Moortgat says that Albert Moortgat traveled to Scotland to source a special yeast for his Victory Ale. A comic strip published by Duvel Moortgat purports to tell the story of that journey. In the comic, Albert is seen traveling with an aluminum milk can, which he supposedly used to transport yeast from William McEwan’s Fountain Brewery in Edinburgh.

There are conflicting opinions about the veracity of this story, with La Chouffe co-creator Chris Bauweraerts believing that the yeast came from William Younger’s beers rather than those of William McEwan (the importer John Martin was bringing Younger’s beers into Belgium at the time). Belgian journalist Katrien Bruyland has suggested that there was no journey at all, but that yeast was harvested from Scottish bottles with the help of a world-renowned yeast expert, Professor P. Biourge. Duvel Moortgat’s own quality director, Dimitri Staelens, suggests the original Victory Ale may have been closer at that time to a Belgian Scotch ale than to the pale, drier style that modern-day Duvel would come to define.

In the 1960s and early 1970s, Emile Moortgat, representing the third generation to run the brewery, formed a strong allegiance with Professor Jean De Clerck, one of the brewing world’s most influential scientists and scholars. Brussels-born De Clerck founded the European Brewing Convention, wrote the canonical two- volume Textbook for Brewing, and helped the monks at the Abbey of Notre Dame de Scourmont create the famous dark, strong Trappist ale Chimay Blue. De Clerck was the best in his field. In the 1960s, he worked to isolate strains from Duvel’s original Scottish yeast to deliver a cleaner, purer, paler beer.

While the production of Duvel involves a whole range of complex processes, there are three aspects of its construction that have most contributed to its iconic status. The first is the fact that it is extremely pale. The second is its fermentation profile, both in performance and in flavor. The third is its very high carbonation. All three elements are integral to the creation of a golden strong ale in the authentic Belgian fashion.

It’s often said that people drink with their eyes, and a very light, pale blonde color has long attracted beer drinkers. Belgian tripels and blonde ales generally start on the color range at about 4 SRM (8 EBC). American IPAs, for comparison, typically begin at about 5 or 6 SRM (11 EBC). Pale lager is the most consumed beer style in the world. Part of what differentiates a Belgian golden strong ale is that it has the enticing appearance of a pale lager. Duvel clocks in at a very pale 3 SRM (6 EBC) on beer’s color scale—or “sometimes lower,” according to Staelens at Duvel.

Duvel’s sole malt, pilsner, contributes the light biscuity notes and pale blonde color; the sugar addition boosts the ABV while keeping the body thin. While brewers at Duvel Moortgat do not reveal the exact ratio of sugar to malt, Staelens says that it can be easily discovered by anyone with good density-measurement equipment. “In order to make a heavy bill, it’s not a small portion” of sugar, he says.

One of the most important ways the brewers at Duvel ensure that the color is very pale is by minimizing what is called “thermal load.” Heat darkens beer. Keeping your wort at high temperatures for a second longer than required will result in a darker beer than you might otherwise obtain.

There are several examples of Duvel’s obsession with minimizing thermal load. Their mash tuns have been manufactured with Steinecker’s ShakesBeer technology, with “pillow plates” and “vibration units.” These help to distribute steam-powered heat to wort much faster, reducing the time it takes to reach target temperatures. They also facilitate more homogenous mixing during the mash, preventing caramelization or other Maillard reactions that would darken the wort. The brewery uses no mixing arm in their mash tuns because it would introduce dissolved oxygen, and that can also darken the wort.

The Duvel brewing process also uses multiple centrifuges, which separate solids from liquid by centrifugal force. Duvel Moortgat doesn’t use a whirlpool, a common vessel used to spin the wort and separate hop matter from the liquid. Instead, they pull wort through two centrifuges—“the biggest wort centrifuges in the world,” according to Staelens—dramatically shortening the cooling time of the wort. This greatly cuts the time it sits at higher temperatures, further reducing the thermal load.

There are, of course, other techniques to ensure a very pale beer. Staelens says that one of his most important regular quality meetings is with the three or four companies who supply pilsner malt to Duvel’s tight specifications. In addition, the brewers don’t add sugar to the boil, a process which would also darken beer, but rather add liquid sugar inline post-boil.

Outside of a few higher-gravity gueuzes and saisons, Duvel is one of the driest beers in its alcohol range in Belgium. The original gravity target is around 1.069 (16.9°P) and generally finishes around 1.005 (1.3°P). The yeast eats deep. This dryness is a major part of what makes Belgian golden strong ale so drinkable, despite its strength.

The flavors created by this deep fermentation are perhaps not as pronounced as you might expect from a Belgian ale, often known for a marked fruitiness and spiciness. In his time as sommelier at Duvel Moortgat, Nicolas Soenen would often describe Duvel’s yeast profile as “neutral” or “pure.” In his recent discussions with Doug Piper on a Gourmet Brewing webinar, Duvel Moortgat brewing engineer Sven De Kleermaeker also described it as “pure.” Sam De Belder, site manager for Duvel Moortgat in Breendonk, uses the word “clean.” Staelens, the quality manager, describes it as “simple but complex.”

The brewery keeps yeast flavors in check through a rigorous set of fermentation specifications. They pitch the Duvel yeast into wort of 68°F (20°C), allowing it to rise 79°F (26°C) during a four-day primary fermentation. It’s at this temperature that the brewers have found what they consider to be the optimal ester- and phenol-compound production. Unlike other breweries that maintain fermentation temperatures by cooling their tanks with glycol or 32°F (0°C) ice water, Duvel Moortgat employs a “Delta T” approach—the coolant is never more than 18°F (10°C) different from the fermentation temperature. “We control stress level on the yeast and do not let it ferment in too rapid a time because it will give a different flavor and aroma profile,” says De Belder.

Once fermentation is completed, usually after four days, they cool the beer to 28°F (-2°C) for 20 days of lagering. It then runs through a series of three centrifuges that remove particles and haze of various sizes. After priming, it referments in the bottle for two weeks in one of four large warm chambers, each 50 meters long, and then undergoes another six weeks cold-conditioning in the bottle before it goes out to market. The whole process from mash-in to sale takes about 90 days, a timeframe that very few top-fermented beers in Belgium enjoy. It would be possible to produce Duvel in a shorter timeframe—perhaps by shortening the cold-conditioning times in the lagering tank or after refermentation in the bottle—but such shortcuts could be detrimental to the beer’s quality as well as to its reputation.

The third major differentiator of the Belgian golden strong ale is its high carbonation. Duvel is saturated with 8.5 grams per liter of CO2, or 4.3 volumes. For comparison, most English ales are carbonated between 2.9 and 4.3 g/l (1.5 to 2.2 volumes), and American ales are usually between 4.3 and 5.7 g/l (2.2 to 3 volumes). Essentially, that half-glass of foam that appears in the large ballon is part of what they’re selling. Such a high carbonation level accentuates carbonic bite, and it ensures that the beer is champagne-esque in presentation and refreshing in consumption.

In recent years, less yeast has appeared in the bottom of bottles of Duvel than in years previously, with some consumers suggesting that the beer no longer undergoes refermentation in the bottle. However, this is not the case. There is yeast there, just less than before. After all, there are disadvantages to having too much yeast in your bottle. It can contribute negatively to foam formation. Over time, there may be autolysis (a process whereby the yeast eats itself and produces off-flavors that may be broth-like, meaty, or sulfuric.)

It’s likely that changes in hot-side production over the years have minimized colloidal instability in Duvel, thus reducing protein and hop trub sedimentation downstream, including in the bottle. However, more significantly, the Duvel brewers have honed their yeast-dosing rates for bottle conditioning in precise ways.

Before refermenting in the bottle, the brewers force-carbonate Duvel to about 5 g/l of CO2 (2.55 volumes) before they add fresh yeast and sugar to hit their saturation target.

That base level of carbonation is a kind of safety blanket. It eliminates issues relating to the stratification of CO2 in large tanks, and it assists when capping bottles—the foam helps to ensure that no oxygen is in the bottle headspace when the bottles are filled. They dose only as much yeast as they need. They also have worked to ensure that their bottle-conditioning yeast strain is extremely flocculent, eventually dropping out and sticking to the bottom of the bottle. Thus, there is no exaggerated sedimentation—and no yeast autolysis. The beer is as bright as a new pin.

The high level of carbonation does present challenges for packaging Duvel in formats other than their steinie bottle. Most draft systems can’t deal with the pressures required to maintain and serve beer at such a high carbonation level. However, Duvel Moortgat has developed a special draft system with specific diameters and lengths for the tubing between the keg and the tap and with specific temperature requirements. The brewery finally released Duvel on draft in 2018.

Meanwhile, cans are less pressure-resistant than glass, so they’ve also released a canned Duvel Single that does not undergo a secondary refermentation.

There are other golden strong ales in Belgium that have been around for decades: Delirium Tremens from Brouwerij Huyghe (1988), Sloeber from Brouwerij Roman (1983), Satan Gold from Brouwerij De Block (1986), and Hapkin, originally brewed by Brouwerij Louwaege, but produced by Alken-Maes since 2002. More recent competitors include Omer Traditional Blond from Brouwerij Omer Vander Ghinste (2008), Keizer Karel Ommegang from Brouwerij Haacht (2012), and Filou from Brouwerij Van Honsebrouck (2015).

In 2020, AB InBev released a golden strong ale called Victoria. The ABV is 8.5 percent, same as Duvel, and the name recalls Duvel’s original incarnation, Victory Ale. The label of AB InBev’s Victoria shows an angel holding the devil to the ground; the visual lacks subtlety, while AB InBev says it comes from the story of the archangel St. Michael’s triumph over the devil.

Those that try to chip away at Duvel’s place as the most successful Belgian golden strong ale on the market are sometimes called “Duvel killers” by Belgian beer enthusiasts. Many have tried. None have yet succeeded.

Known for their high-gravity beers and irreverent attitude, the Struise Brouwers have injected fresh energy into Belgian beer over the past two decades. Yet the systems they’ve built to brew these big beers are as creative as the beers themselves.

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