Oud Bruin, or (east) Flanders Brown, refers to a blended sour dark ale style that was common in the province of Limburg in the Netherlands and is still popular in the East Flanders city of Oudenaarde in Belgium. The name “oud” (old) refers to the lagering or aging process that can take over a year to complete. If performed in traditional oak vessels, bacteria and wild yeasts residing within the wood will change the beer until it develops a variety of cherry, plum, and raisin-like aromas and fruity flavors, with a slightly acidic and astringent finish. Many of these characteristics are more readily associated with wine than beer. Traditionally it is then blended with younger and sweeter beer to reduce the acidity and introduce the sweetish caramel malt notes that make it more complex and palatable. There are also versions that are neither fermented in wood nor blended and that are drier, hoppier, and more metallic in character. A distant relative of the Flanders red ale, the two styles are often confused and some consider them to be one and the same. Stylistically speaking, however, Flemish brown does not show the “barnyard” Brettanomyces character often present in Flemish red, whereas Flemish red misses the deeper color and caramel nuttiness common in “Vlaams Bruin.”
Oudenaarde is considered to be the capital of the style, but to make matters confusing, the geographical location of the brewery used to define which variation of the style was brewed. The city, which is split by the Schelde River, was also split by the Treaty of Verdun from 843 ce. The kingdom of France and its brewers were located on the northwest bank and brewed sweet–sour versions, using gruit as their flavoring preservative, while their German counterparts on the southeast brewed a hopped version with a light roast character.
Oud was a refreshing blended beer popular in the Netherlands until World War I, before the introduction of refrigeration and lager beer. It was born out of necessity, similar to other blended beers of the same era such as porter.
The Dutch still produce an artificially sweetened and colored lager version of this style popular with the elderly, nursing mothers and athletes looking for a sweet pick-me-up without the caffeine in cola. Confusingly called “Oud Bruin,” it varies from 2%–3.5% ABV and typically has a low bitterness of about 12 IBU.
The Gulpener brewery in the Dutch Limburg village of Gulpen, nestled between Belgium and Germany, reintroduced Mestreechs Aajt in 1984. The base beer for this blend is spontaneously fermented for 11 to 13 months in wooden barrels at De Zwarte Ruiter pub close to the brewery. About 25% of this beer is blended with two other commercial beers, an Oud Bruin at 3.5% ABV and their Dort at 6.5% ABV. The “wild” spontaneously fermented beer, referred to as “oerbier” in the brewery, is quite sour and the Oud Bruin tastes artificially sweet (from saccharine) and is mouth-coating. The final product, Mestreechs Aajt, has a sweet-and-sour character that is totally unique and unlike other Flemish brown ales. Former brewery director Paul Rutten once said, “The taste is so strange that there is very little market for it in Holland” and that it is only brewed to maintain and promote the blended beer tradition. Gulpener stopped producing Meestrechs Aajt in 2005 due to hygiene law issues with the local food and health authorities and has only recently announced plans to reintroduce it. In March of 2009 De Molen brewery from Bodegraven in the province of South-Holland, in collaboration with the Amager Brewery from Denmark, released a 5.7% ABV version of the Flemish brown style called “Vlaams & Hollands” (Flemish & Dutch). It is fermented using a lactic culture and lagered for 4 months in Bordeaux wine and Dutch whiskey barrels. Traditional Belgian examples of sour Flemish brown ales are Cnudde Oudenaards Bruin (4.7% ABV; only available on draught in the direct vicinity of the brewery), Verhaeghe Vichtenaar (5.1% ABV), and, for stronger versions, Liefmans Goudenband (8% ABV) and De Dolle Brouwers Oerbier Special Reserva (12%–13% ABV). Fine non-soured examples are Roman Adriaen Brouwer (5% ABV) and a stronger version called Adriaen Brouwer Finest Dark (8.5% ABV).