Oud Bruin (Old Brown) also known as Flanders Brown, is a beer style that originates from the East Flanders province, within the Flemish region of northern Belgium.
A lightly soured style, Oud Bruin is considered a close relative of the Flanders Red style, as they have many similarities. Names can be deceiving though, as color largely overlaps with Oud Bruin's, reaching only slightly further into the darker spectrum, and Flanders Red into the lighter. Oftentimes beer will be labeled using both color descriptors, such as Flemish red/brown ale, making clear categorization a bit more difficult. The most noticeable differences between the two are that Oud Bruins are brewed with more dark malt, resulting in more malty, caramel-like, and dark fruit flavors, and are generally aged in stainless steel rather than wood barrels, which produces a softer acidity.
Using multiple yeast or bacteria strains, known as mixed fermentation, produces a beer of great complexity. Ale yeast in addition to multiple souring bacteria's, most often added intentionally, but sometimes spontaneously by letting the wild yeast in the atmosphere takeover, will produce the soft sour character typical of the style. After fermentation, they are generally aged for several months or years, and then blended with young (freshly brewed) beer, to tone the acidity down, add some sweetness for balance, and provide some new sugars for conditioning in bottled versions.
While freshly brewed examples are quite good, this style only benefits from extended aging, which produces a more pronounced sour character and sherry-like qualities from gentle oxidation, among other benefits. Cellaring these beers for 10 years or more is common. Even with age though, these beers should never be overpoweringly sour or vinegar-like.
The best examples can exhibit flavors and aromas of raisins, figs, cherries, chocolate, caramel, and nuts. Bitterness is very low, and hop flavors are generally unnoticeable. Brewers often use these advantageous flavors when blending the base beer with fruit to produce variations. Try the Liefman's Cuvee-Brut or Kriek Brut blends. They're among my favorite fruited beers.
Liefman's brewery, with roots as far back as the 1600's, exemplifies the Oud Bruin style admirably. They produce several variations, with Goudenband being a higher ABV blend of more mature (older) beers. This is a perfect mid-level sour enthusiasts choice. If you're is looking for an approachable sour without the extreme lip puckering quality often associated with sour beers, you have found a perfect match.
Adam Roberts is a Certified Cicerone.