Belgian Red Ale is a specialty of the northwestern province of Belgium, West Flanders. The beer is characterized by a red to brown hue and a balanced but assertive acidity. The fermentation process is typically done through a mixed fermentation of yeast and lactobacilli, followed by a long aging on oak barrels. This brewing and fermentation process is closely related to that of the Belgian sour brown ales, and although English speakers now differentiate the two styles, the Belgians do not; they use the term “sour brown beer” for both.

Belgian red ales are regional session beers with alcohol contents hovering around 5% alcohol by volume and show a mild refreshing tartness. The Rodenbach Brewery of Roeselare has long been the anchor of this category of beer. See rodenbach. In the early 1870s Eugene Rodenbach did an apprenticeship in a brewery in England and came back with a process that was very close to what Obadiah Poundage described as the origin of porter beer. Fresh beer was blended in the pub—and later in the brewery—with beer that had been aged for 2 years on oak barrels and acquired a distinctive sour complexity. See porter.

The Rodenbach Brewery makes two different brews. Both brews are made from a base Munich malt of around 9 European Brewery Convention (4.5 standard reference method), some caramel malts, corn grits, and spices. They are lightly hopped for a bitterness of around 12–20 international bittering units in the beginning of the boil. The heavier beer, with an original gravity of around 13° Plato, goes through a week-long mixed lactobacilli–yeast fermentation. The settled yeast is removed and the beer goes through a primary aging of 6 to 8 weeks in horizontal tanks at around 15°C (59°F) to settle the remaining yeast and develop the lactic acid anaerobically. The secondary aging follows with 18 to 24 months in vertical oak vats, each holding between 100 and 660 hl (85 to 560 bbls). The beer microbiology develops mainly lactic acid, acetic acid, and the ethanol esters of those acids, ethyl lactate and ethyl acetate. The wood is porous and cannot be sterilized, so the microbiology is different from barrel to barrel, containing Saccharomyces and Brettanomyces yeast and lactic and acetic acid bacteria. A sturdy pellicle (skin) forms on top of the beer, bound by filamentous yeasts. After the secondary aging in oak, the beer used to be bottled straight as Rodenbach Grand Cru. Today, the assertive sourness of the Grand Cru has been cut down by dilution with a lighter blending beer. The lighter blend beer is brewed at 11.5° Plato with the same weeklong mixed fermentation, followed by an aging for 4 to 6 weeks in stainless steel metal tanks to further develop some lactic sourness. The lighter brew blended at higher proportions to the wood-aged beer leads to a very drinkable, thirst-quenching red-brown ale, simply called Rodenbach.

At one time, the Rodenbach Brewery used to sell its yeast to breweries within a 50-km (30-mile) radius of Roeselare, and these breweries made their own Belgian red, sour brown, or other beers with it. Sharing yeast has been very common in breweries in Europe. The mixed yeast slurry was used for mixed fermentation in Ichtegems from the Strubbe Brewery, Liefmans and Goudenband from the Liefmans Brewery, Oerbier from the Dolle Brouwers, Vichtenaar and Duchesse the Bourgogne from Verhaeghe Brewery, Felix from Brouwerij Clarysse, and Damy Brewery in Olsene. Some breweries used this yeast also for bottle conditioning or even to ferment a Tripel with it, as in the Guldenbergs Brewery. Regional and family politics led to some breweries maintaining their own processes, such as the Bockor, Bavik, and Van Honsenbrouck breweries focusing on a regular main fermentation with a long aging on wood afterward leading to beers like Bellegems Bruin, Petrus, and Bacchus.

Rodenbach stopped distributing their yeast in 1999, leading to no small resentment and resulting in new fermentation strategies at the surrounding breweries. Brewers had relied on long-established processes within their own breweries that were based upon symbiosis with Rodenbach, but now they faced a challenge as their yeast supply vanished. Breweries like Liefmans started to maintain their own mixed fermentations. Strubbe Brewery changed to wood aging to make the Ichtegemse Grand Cru. The Dolle Brouwers puts part of the beer through a souring fermentation in a separate tank.

When traditionally brewed, the sour red beer style is complex, balancing a backbone of lactic acidity with sherry-like fruit notes. The best of them can be very elegant and wonderful with food. Rodenbach and other sour beer brewers have struggled to transition from being strong local brands to players on a larger stage. The segment has always been a minor but relevant part of the Belgian beer scene. See belgium. Red ales are exported worldwide as unique specialties but have gained a foothold in the United States with the growth of the craft brewing industry.

It now seems that Belgian red ales will develop niche markets where creative brewers are active. Sour beers are late to arrive in a developing craft beer market as we see in the United States, Italy, and, to a lesser degree, France, Canada, Japan, and a few other countries. In the United States in particular, they have helped, along with lambics, to spark an entire new category of sour beers. The endeavor to work with microorganisms other than yeast is always a risky step for a brewery; it involves intentionally culturing microbes that most breweries do their best to eradicate. However, the production of such beers is a creative outlet for brewers who have explored the classic sour styles and wish to attempt new and interesting iterations within the genre.