A sour beer aged in wood or in contact with wood, taking its acidity from bacteria living in the barrel or introduced during fermentation. The wood — often a used wine, sherry, rum, or whiskey barrel — adds tannin and complexity, while Lactobacillus and Pediococcus build a lactic, sometimes acetic, sourness over months or years of maturation. Base beer and strength vary widely; what defines the category is the marriage of wood character with bacterial acidity.
In the glass
Origin
Aging beer in wood predates stainless steel entirely, and in the Belgian sour tradition the practice never lapsed. Flanders red ales and oud bruins have been fermented and matured in large oak vessels for generations, where resident bacteria sour the beer slowly as it ages; Rodenbach’s foeder hall in West Flanders is the archetype. American craft brewers drew directly on that model as the sour and wild beer movement took shape, building their own foeder and barrel programs. New Belgium’s La Folie, a wood-aged sour brown developed by Peter Bouckaert after he came to Colorado from Rodenbach, matures for years in French oak foeders that hold one of the oldest continuously maintained souring cultures in American brewing. Brewers then pushed beyond imitation, aging sour beer in spent wine, bourbon, and whiskey barrels and blending across casks the way gueuze blenders do, to build complexity no single barrel could reach.
Notes
The distinction that matters here is what does the souring. A wood-aged sour beer in the strict sense takes its acidity from bacteria — Lactobacillus and Pediococcus — rather than from wild yeast; beers whose character is driven by Brettanomyces belong in the Brett or mixed-culture categories instead. The wood is not just a container: a neutral oak barrel contributes tannin and a little vanilla, while a barrel that held wine or spirits layers in those flavors on top of the acidity. Because each barrel or foeder matures on its own schedule, blending across vessels is central to the craft, and the same brewery’s release can taste meaningfully different from year to year. The range runs from bright, vinous Flanders-style reds to dark, fruit-laden sour browns.
Defining examples
New Belgium La Folie·Cascade Kriek·The Bruery Oude Tart·Rodenbach Grand Cru·Almanac Farmer’s Reserve