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Flanders red and Oud Bruin - the Belgian art of sour beer

Belgium is not only lambic. In the region of Flanders two other, unique styles of sour beer were born: Flanders red and Oud Bruin (Flemish brown). They are beers of a surprising, winey acidity, far from sweetish industrial beers. Flanders red, famous thanks to the Rodenbach brewery, matures in large oak barrels and has a fruity-acetic, almost winey character. Oud Bruin, associated with Liefmans, matures in steel and is more gently sour, more malty and soothing. Both are joined by the art of blending - mixing young and old beer. They are two faces of Belgian sour craft. Here is a guide to Flanders red and Oud Bruin: where their acidity comes from, how they differ and why blending is key here.

Two styles from Flanders

To understand both beers, you have to know their origin. Both were born in Flanders, but in different parts of it. Flanders red comes from West Flanders and is famous thanks to the Rodenbach brewery from the town of Roeselare, operating since 1821. Oud Bruin, that is Flemish brown, comes from East Flanders and has a centuries-old tradition - the Liefmans brewery has been making some form of this style since the 17th century. They are two related but distinct styles of sour beer, each with its own tradition and method. A curiosity: before the famous beer writer Michael Jackson wrote about these beers, Belgian brewers did not make such a sharp distinction between red and brown - it was largely he who framed these styles. Understanding that they are two Flemish styles of a shared, sour lineage is the starting point for the rest. We cover sour beers more in sour beers.

Where the acidity comes from

The key feature of both beers is their acidity, far from ordinary, clean beers. It comes from fermentation with the participation of wild yeasts and bacteria, not only ordinary brewer’s yeast. Flanders red begins with fermentation by Saccharomyces yeast (like any beer), but then maturation in the barrel adds a whole range of bacteria and wild yeasts. In play are Lactobacillus (lactic acidity), Brettanomyces (wild notes, funk) and Acetobacter, giving acetic acidity. This interplay of many microorganisms builds the complex, sour depth of these beers. The result is a winey acidity, fruity-acetic, sometimes almost like balsamic vinegar, far from sweetness. This is why Flanders red is sometimes called the most winey of beers. Understanding that the acidity comes from wild fermentation explains the character of both styles. We cover these bacteria more in bacteria in beer.

Flanders red: oak and fruit

Flanders red is a style of a beautiful, red-brown colour and an expressive, fruity-acetic character. Its secret lies in the maturation: the beer rests in large oak barrels called foeders, sometimes even up to two years. It is precisely the oak and the long maturation with wild microbes that build its character. Flanders red is less malty-rich than Oud Bruin, but more fruity-tart and acetic. It is described as startling, quenching and fruity, distinctly sour with a capital S. In the flavour you sense red fruit (cherry, plum), a note of vinegar, oak and a winey depth. It is a beer that many compare to a light, sour red wine. The most famous representative is Rodenbach, maturing in hundreds of oak foeders. Flanders red is the fruity, acetic, winey face of Flemish sour beer. It is a style for lovers of expressive acidity.

Oud Bruin: steel and malt

Oud Bruin, that is Flemish brown, is the counterweight to the sharp red. The key technical difference: Oud Bruin usually matures in steel tanks, not in oak barrels. This makes it less acetic - without contact with wood and oxygen it develops differently. Oud Bruin has a lower, gentler acidity, mainly lactic, plus a richer, malty character. In the flavour notes of coffee, raisin, caramel and chocolate dominate, with a subtle, soothing sourness in the background. It is described as rich, bready and soothing, in contrast to the startling, quenching red. It is a gentler, sweeter and fuller beer, where the acidity is a discreet addition rather than the main theme. Oud Bruin is the malty, gentle, soothing face of Flemish sour beer. The most famous representative is Liefmans. It is a good choice for someone who wants to get to know sour beer, but in a gentler, more malty form.

A table: red versus Oud Bruin

Let us gather the two styles in one place:

The table shows the heart of the difference: red is oak, fruit and a sharp acetic acidity, Oud Bruin is steel, malt and a gentler, lactic sourness. They are two faces of Flemish sour beer.

The art of blending

The shared and key element of both styles is blending, that is mixing beer of different ages. It is the art of the master of the blend. Flanders red matures up to two years in oak foeders, and then different barrels are mixed, to create the final product of a desired balance. Bottled versions are often a blend of old and young beer: the old brings depth and acidity, the young freshness and a lively character. The brewery must skilfully choose the proportions, to get a harmonious whole - too much old gives too sour a beer, too much young too flat. It is a craft close to winemaking, where the blender composes the flavour from different vintages and barrels. Blending allows a consistent, balanced profile to be achieved despite the unpredictability of wild fermentation. This is why Flemish sour beers are not single batches but compositions. The art of mixing is as important here as the fermentation. We cover the blending of sour beers more in lambic and gueuze.

Why it matters for flavour

Understanding these two styles opens the door to the world of Belgian sour beer beyond lambic. Flanders red shows how a beer can be almost a wine - fruity, acetic, quenchingly sour, maturing in oak like a good drink. Oud Bruin shows the gentler, malty side of acidity, soothing and rich. Together they broaden the understanding of how diverse sourness in beer can be and how much depends on the maturation (oak versus steel) and the blending. They are beers for someone who wants to go beyond the sweet, clean styles and get to know the complexity of wild fermentation. They are also great company for food: the acidity of the red beautifully cuts through fatty dishes, and the malty Oud Bruin suits game or cheeses. For an enthusiast it is a fascinating journey into the depth of the Belgian tradition. It is worth trying both, to feel the two poles of Flemish acidity. It is a discovery that broadens beer horizons.

How to sense it in the glass

Both styles are easy to tell apart once you know what to look for. Flanders red: red-brown colour, clear, acetic-fruity acidity, notes of cherry, plum, vinegar and oak, a quenching, almost winey character - sour with a capital S. Oud Bruin: darker, brown colour, a gentler, lactic sourness in the background, rich notes of coffee, raisin, caramel and chocolate, a soothing, malty character. If a beer is clearly acetic, fruity and quenchingly sour, it is a clue for red; if malty, soothing and only subtly sour, Oud Bruin. It is worth trying Rodenbach and Liefmans side by side, to feel the contrast of oak and steel. Serve them lightly chilled, best with food. Over time you will start to recognise both styles by their acidity and character. It is a higher level of appreciating Belgian beer.

The essentials in brief

Let us gather it up. Flanders red and Oud Bruin are two sour styles of beer from Flanders. Flanders red from West Flanders (the famous Rodenbach) matures in large oak barrels (foeders), has a higher, acetic-fruity acidity and a quenching, almost winey character. Oud Bruin from East Flanders (Liefmans) matures in steel, is less acetic, of a gentler, lactic sourness and a richer, malty profile with notes of coffee and raisin. The acidity of both comes from wild fermentation (Lactobacillus, Brettanomyces, Acetobacter). The shared key is blending - mixing old and young beer for balance. Now you know where this acidity comes from, how the two styles differ and why blending is an art here.

Note every beer in GustoNote - including the style and the acidity you sense. Over time you will start to recognise the oaky, acetic red and the malty, gentle Oud Bruin.