On September 29th Republic at Seven Corners is playing host to an event called Where the Wild Beers Are. They are calling it a “collaborative” festival for wild beer enthusiasts—think of it as a sort of potluck for wild beer. The cost to attend the event is $10 plus your beer contribution. For every 750 ml of sour beer you will receive 10 tickets for beer samples, assuring that everyone gets an equal amount to try. This is the 5th year that this event has taken place in the Twin Cities; bringing together fans of “wild or sour” beers—a style that originated in Belgium where wild yeast is introduced to the wort via open fermentation. Jeff Halvorson and Tim Stendahl are the men behind this event, as well as the one held in Brooklyn, New York.
The process of creating a sour or wild beer can be rather lengthy; often taking years for the beer to properly mature. Debuting at this year’s event will be Mark 1 and Mark 2, which are two special sour beers created by some of the previous year’s attendees from the bacteria and yeast left behind in the bottles at last year’s event. The ten-month old Mark 1 was made with white wine-soaked oak staves, while Mark 2 will feature cherries.
So, you may be asking yourself: Just what is a sour beer and what is the difference between regular and open fermentation?
According to University of Minnesota Associate Professor of Microbiology Jeff Gralnick, the difference between open fermentation and normal fermentation is all about how you “inoculate” the fermentation. “The open fermentation style in many cases is literally a fermentation vessel that you leave open to the air. Microbes floating around in the air (typically this can be around 100,00 per square meter) have a chance of landing into the vessel. The majority of things that land probably don't know how to live in this environment, but some of them do.”
One might wonder where an ideal place to execute an open style fermentation would be. “Sometimes these open fermentations are done in orchards, where the number of microbes who really like to ferment sugars can be higher in the air (think about rotting fruits, for example),” Jeff said. It may also be as simple as reusing your fermentation vessel, “In the next batch, the microbes can come from the nooks and crannies in the wooden vessel when it is reused.”
And just what, exactly, creates those unique, sour flavors? According to Jeff, “Often these wild microbes (both yeast and bacteria) make sour and funky tasting compounds in addition to ethanol, which an organism like Saccharomyces (the yeast species typically used in making beer) typically don't make.”