What is a Sour Beer?

Sour beers, also labeled “wild,” are made by intentionally inoculating the wort (sugary liquid that turns into beer) with wild yeast strains. These beers can be anywhere from slightly tart to massively sour.

Any beer can be made “sour” and there are various ways to accomplish the task. One way, often utilized by Belgian brewers is to “open ferment” in coolships, or large shallow vessels used to cool the wort with nothing but open night air. This technique allows wild organisms (bacteria and yeast) to settle on the wort and feast on the sugars. Other brewers will choose ahead of time what types of wild yeast they want to add to their beers and will simply add a culture of that bacteria or yeast to the fermentation vessel. Barrel aging can also add a sour characteristic to beer, as wood is the perfect breeding ground for wild organisms.

Different beer styles have varying degrees of tartness, and those that don’t fit within traditional style guidelines, are a mix bag. According to the Beer Judge Certification Program (BJCP) guidelines there are six recognized styles of sour beer: Berliner Weisse, Flander’s Red, Flander’s Brown (or Oud Bruin), Lambic, and Geuze (also spelled Gueuze), plus “Fruit Lambic”. Farmhouse saisons, depending on the yeast(s) used to ferment, may also offer a low to moderate tartness, but isn’t considered one of the classic “sour” styles.

Berliner Weisse’ heritage lies in Berlin, Germany as you might guess. Classically, it is a pale in color, low ABV beer made mostly of wheat that is tart and refreshing. It’s brewed with traditional ale yeast and lactobacillus, one of our “wild” friends responsible for the pucker. Very few German breweries produce the classic style anymore, but some American craft breweries have adopted it with their own interpretations. On a sour scale of 0 (not sour) to 10 (the most sour thing ever consumed) I’d rank Berliner Weisse a 2 – 3.

Flander’s Red Ale is a very complex, oak aged beer, historically produced in West Flanders. It is typically a deep red or reddish brown color with flavors and aromas of dried fruits, cherries, and a pleasant sweet-tart balance. ABV is usually in the 5-7% range. The so called “Burgundy of Belgium,” this beer is the most wine-like of all beers. It would be a good introductory beer for the wine lover in your life. In terms of tartness, I’d rank Flander’s Red as a 4 – 6 on the sour scale.

Flander’s Brown Ale, or Oud Bruin (indigenous to East Flanders) differs from Flander’s Red in that it is typically less sour, less fruit forward and not usually oak aged. The malt flavor comes through more in these more mellow beers. Flander’s Browns have a wider range of ABV’s and are usually darker in color than Flander’s Red. Flander’s Brown ales offer a more elegant and refined sour flavor perfect for the adventurous craft beer lover who wants to start off with a more demure sour flavor, a 3 – 4 on the sour scale.

Lambic is a wild, spontaneously fermented beer made only in the Senne Valley of Brussels, out of unmalted wheat, Pilsner malt and aged hops (the aged hops offer no flavor but are used for their preservative powers). They are golden in color and extremely complex. Lambics are typically uncarbonated, single year versions, where Geuze, is a blend of three different years of Lambic that is highly carbonated. They are both refreshingly tart with aromas of hay, horseblanket, and flavors of tart pear. Lambic and geuze can offer substantial sour flavors, usually a 5-7 on the sour scale.

Fruited Lambics may be sweet and not very sour at all. The most common versions are kriek, or cherry lambic, and framboise, or raspberry lambic.

American Craft Breweries have started to create their own versions of sour styles which are typically referred to as “wild ales”, or even labeled using names of the organisms they use. They range in their level of sourness from just barely tart from a touch of Brettanomyces to bracingly sour, just loaded with wild microrganisms like pediococcus and lactobacillus.

A well done sour beer is absolutely delicious. It can take years for the flavors to come together the way the brewers want, and can even require blending of different beers/years. A labor of love indeed.