I’ve run across this question/assumption quite a bit lately and decided to tackle it for this edition of Q & Ale. Are all sour beers spontaneously fermented?

I can understand where this assumption comes from and why it’s so prevalent. The popularity of sour beers or “wild” beers is a relatively new phenomenon. While these beers have been around since the invention of beer, they were a small and dying niche until the craft beer resurgence began. Now they are a hot, but still misunderstood, commodity. Additionally, spontaneous fermentation is a relatively easy and romantic thing to understand.

To answer the question: No, most sour/wild beers are NOT spontaneously fermented.

Throughout history, most beers would have been spontaneously fermented in some part. People didn’t know about microbiology or the yeast that caused fermentation. The wort was allowed to sit in the open air until it started fermenting on its own. Yeast and bacteria that were present in the air would have settled in to start the process. Brewers then could scoop some of the froth off and start another batch of beer.

Today’s spontaneous fermentation operates in a very similar fashion. The wort is placed in a large, shallow vessel called a “coolship” where it can cool overnight while being exposed to the ambient air. The beer is then transferred into barrels where it continues to ferment. Additionally, these barrels become home to a wide variety of yeast, wild yeast, and bacteria that will continue to ferment the beer while adding a huge depth of character. This process take a long time to complete. While spontaneous fermentation was the original method of beer making, today it’s confined to the beers of Lembeek region of Belgium, known as “lambics” and “geuzes,” and to a few adventurous American breweries.

Russian River Brewing, of California, produces one spontaneously fermented beer called Beatification. Allagash Brewing, from Maine, has an entire line of spontaneously fermented beer called “Coolship.” Yet, these are a small percentage of the sour beers produced by each brewery and a incredibly small portion of the beers produced overall. As far as I know, there is only one US brewery making all their beers via spontaneous fermentation: De Garde Brewing. De Garde opened earlier this year in Tillamook, Oregon. I’ve had a few of their beers and so far, they’re fantastic.

The major problem with spontaneous fermentaion, besides having less ability to control the process, is that you have a limited window to brew beer. Lambic breweries only brew from fall through spring. Most lambic breweries stop brewing by early April. Once the air warms up enough in mid-spring, more varieties bacteria, particularly spoilage varieties, become active. That’s why the Rheinheitsgebot forbid brewing during the summer. Yeast and wild yeast are much more active than bacteria during the cool and cold months. This allows spontaneous fermentation breweries to get the right mix of microbes in their beer.

The vast majority of sour beers are produced in a much more controlled manner. New Belgium La Folie (their Flemish-style red) undergoes a standard yeast fermentation (no wild yeast or bacteria) and is then placed into a foeder where wild yeast, brettanomyces, and various bacteria live. That’s where the beer is soured. Rodenbach goes through a mixed fermentation. They pitch a mix of 80% standard yeast and 20% a house cocktail of bacteria and wild yeast. The beer then goes into the foeders to continue developing.

Brett beers, using the brettanomyces yeast strain, are another variety of popular “wild” beers. Usually, the beer undergoes standard fermentation but then undergoes a secondary fermentation in the bottle using brett as the finishing yeast. If consumed fresh, the beer would taste relatively normal, but give it time, and it will turn very funky. Orval is the most famous beer using a variation of this method. There are a whole host of American brewers using this method.

There are many ways to sour a beer; spontaneous fermentation is only one method. Whether soured in barrel, via mixed fermentation, or finished with brett, the result is a tasty concoction that hearkens back to days before yeast was understood and controlled. They’re truly wild beers.

Additional Reading:

If you’d like to read about New Belgium’s sour program, you can read my review of their Sour Symposium.

Take a tour of a spontaneous fermenting Lambic brewery by reading about my tour of Brouwerij Boon.

Learn how Rodenbach makes their beers and view my pictures of their facility.

Want to know more about the microbes involved in sour and wild beers? Read my article “The Yeasties, The Yeasties: The WILD Beasties in my Beer.”

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