In Flanders Fields, the Beer Flows

Brew beer like a Belgian by learning about the quirky sour ales that originated there.

| Spring 2020


Throughout most of the 20th century, a few regional styles of sour beers existed around the world, mostly as throwbacks to a different time. In the late 1990s, sour beers were almost unheard of in North America, except to a small number of brewers and craft beer aficionados. The Great American Beer Festival (GABF), renowned for having a category “for everything,” didn’t add a category for sour beers until 2002. Now, sour beers — both fresh takes on old styles and entirely new ones — are everywhere.

Sour beer production methods deviate from those of “regular” beers in a variety of ways. Obviously, specific steps are required to sour the beer. For a variety of reasons, however, the classic Belgian sour beers — the most famous being the lambics of the Senne River Valley and the sour beers of Flanders — have other production steps that aren’t found in other beers.

What Makes a Beer Sour?

Sour-tasting beers are made by allowing microorganisms to produce tart acids and sour the beer. The organisms most often involved with souring beer are bacteria in the genera Lactobacillus and Pediococcus. Bacteria in both of these genera can break down residual carbohydrates in beer that brewer’s yeast (Saccharomyces cerevisiae) can’t. These bacteria ferment the carbohydrates and release lactic acid, which has a distinctly tart flavor. These microorganisms can also operate in low-pH (less than 4.5), high-alcohol (over 0.5 percent ethanol) conditions. These conditions would inhibit most other microorganisms. Beer can be soured in the mash or the kettle, and some modern U.S. beers are made this way, but classic Belgian sour beers are soured after primary fermentation.

Basic Belgian Sour Beer Production

Brewers of Belgian sour beers produce their wort and ferment in a similar way to other beers. At one or more points in the process, however, the beer is inoculated with bacteria that’ll sour it. In most cases, the not-yet-soured beer is pumped to wooden barrels that’ve been previously used for conditioning sour beers. This inoculates the beer with the appropriate microorganisms. Brewers of sour beers are careful to assess the beer that comes from each barrel. Barrels that produced high-quality beer are used again. If the beer coming from a particular barrel is “off,” that barrel isn’t reused.

Photo by Bernt Rostad.
A guesze is a blended lambic that's made by combining lambics aged in barrels for a number of years.



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