It’s Not Magic, it’s Science: debunking the mystery of sour beer

Sorry beer snobs, sour is not the newest trend in brewing – it’s actually the oldest.

But thanks to its recent rising popularity and an influx of microbiologists into the brewing industry, sour beer has been elevated from a historical product of chance to a contemporary creation of choice. Previously the result of unintended bacterial contamination, the production of sour beer is now a controlled and artful science. And in a modern era when sanitation rules, sours remind us that sometimes it’s good to get a little dirty.

Although certain elements of brewing beer might have seemed magical in centuries past, it was understood well enough even by ancient cultures to become a reproducible process. These societies knew exactly what they were doing with brewing, minus the microbiology, argues anthropologist Travis Rupp, research and development manager at Avery Brewing. They just lacked the modern technology to control certain variables.

That lack of control meant that ancient beer was probably flat, low in alcohol – and sour, Rupp says.

And though it is safe to drink, sour beer is tart and tangy as a result of bacterial contamination. It starts out like any other beer: mashed and boiled grain, a sugary liquid called wort, is fermented by Saccharomyces cerevisiae – good old fashioned brewer’s yeast. This initial fermentation is then followed by the addition of bacteria, which eat the leftover sugars the brewer’s yeast could not. During this special secondary form of fermentation, the bacteria feast and produce lactic and acetic acids. The resulting flavors from these acids can make a beer funky, sour, tart or terrible.

Knowing how to control and monitor this process means the difference between a creating a delicious or a dull beverage.

Ancient brewers had no way to prevent bacteria like Lactobacillus and Pediococcus in the air around them from getting into their beer and causing what’s called “spontaneous fermentation.” These wild beers were open to all kinds of yeast and bacteria, creating one-of-a-kind, locally-influenced brews. But they weren’t always sour, or satisfying. So these days, more and more brewers are adding Lactobacillus and Pediococcus to their beer with a plan.

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Caleb Levar of Oakhold Farmhouse Brewery and Fair State Brewing Cooperative holds open a plate of culture mixed to select for growing hardy strains of yeast and bacteria that will most benefit the souring process.

Microbiologist Caleb Levar used to buy the myth that making sours was simply a mysterious process. But after tasting a homebrewed sour by Levi Loesch in 2010, he realized there was zero magic involved. As he would say, “it’s just science.”

Levar and Loesch are now the primary consultants for Fair State Brewing Cooperative’s sour program and the founders of Oakhold Farmhouse Brewery in Minnesota, which will open its doors in 2017. One of few breweries in the U.S. started with sours specifically in mind, Oakhold is a great example of the challenges and rewards of doing business with bacteria.

Oakhold joins craft industry giants like New Belgium as part of a quickly growing trend in sour beer production. And while sours have been no secret in Europe for the past century, their interest in the U.S. has only flourished since craft beer came back in the 1980s. Today, there are more than 6,000 breweries across the country – far more than the 49 operating in 1983. With this explosion of diversity has come a desire to try new things, to push boundaries and learn as much as possible about the craft.

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A collaboration sour beer made by Fair State Brewing Cooperative and Oakhold Farmhouse Brewery.

At the intersection of scientific experimentation and collaboration, sours are the perfect fit for both curious brewers and drinkers. The evidence is on empty shelves in stores, where bottles that used to sit gathering dust can now barely be kept in stock.

Ten years ago, most beer festival attendees “wouldn’t have any idea what I was pouring,” says Kevin Roberts, sales manager of Abu Nawas Beverage Company, “and I would be frequently asked if it was sour on purpose.”

Today, Roberts is routinely asked if he has anything sour when pouring a set of beers at events.

But despite their newfound popularity, sour beer is difficult to do right. Dan Driscoll at Avery Brewing is in charge of quality control, and knows the difficulties in the process from start to finish.

“Doing any beer really, correctly and properly, is a challenge,” Driscoll said, “but it’s really easy to screw up a [sour] beer.”

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Dan Driscoll at Avery Brewing speaks about their lab and microbiology research as part of the brewing business. Photo by Harrison Dreves.

There are several ways to brew a sour, but wood barrel aging is preferred by many breweries for the complexity of flavors it can create. The beer is transferred into oak barrels before the bacteria is added and the souring begins. This method is known for creating Belgian style sours like Lambics and Gueuzes.

The trick with using wood is that a brewer likely never knows where their barrels are coming from – or what bacterial cultures are already present in them. Like many breweries, Oakhold buys wine and whiskey barrels blindly from wholesalers. So unless a brewery works with a specific vineyard or distillery, they will never know the origin of their not-so blank slate.

To work around this issue of variability, Oakhold both extracts its own bacteria from other beers and splits barrels of previously brewed batches to make more of what they like. Many sours’ unique microflora are linked back to an original liquid from an early batch, like a sourdough starter. But the fact that each barrel must be carefully cultivated means it can take a lot of time to build a bigger series of beers that are consistent enough for distribution. Even Avery, who have been making sours since 2009, finally felt confident in their production consistency as of 2015.

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Caleb Levar stands in front of a set of oak barrels in the basement of Fair State Brewing Cooperative used to make beer for Oakhold Farmhouse Brewery.

But what does consistency for a sour mean?

First and foremost a sour is called a sour because well, it tastes sour. And that funky flavor is present because sour beer contains lactic and acetic acid. Sometimes yeasts are also added during souring, such as Brettanomyces, to enhance different flavor profiles. But strains of Brett. on its own produce very little lactic acid and do not make for a tart drink.

On the other hand, too much of the wrong acid can sour an experience.

“I like a glass of lemonade, not a glass of vinegar,” explains Chris Coyne, co-founder and chief of brewing operations at Sanitas Brewing Co. in Boulder, Colorado.

While the two beverages have the same pH, they are made up of different acids. Acetic acid is one of two ingredients in vinegar, the other being water. So clearly, too much of that would ruin the brew. It can be overproduced if there is too much oxygen available for the bacteria. So while lactic acid is joined by acetic acid in most sours, it does best in small amounts – assuming you want to be able to drink a whole pint.

Acids stop being produced when bacteria run out of sugars to eat or the alcohol content rises to an intolerable level. When this happens, the beer can continue to age and pick up flavors of the barrel without becoming overly acidic. But along the way, brewers taste test to check how their beer is doing. Sometimes fresh or dried fruits or spices are added straight into the barrel. As Coyne says, a brewer can pick the direction a sour takes, but not how far it goes.

And since it’s home to living organisms, he also has to ask, “what does the beer want?”

If a beer tastes like movie popcorn butter or smells like baby vomit, it’s either not ready to drink yet – a normal sign of incomplete fermentation – or it’s been on the shelf too long and got contaminated after production. A byproduct of fermentation, the buttery compound diacetyl is reabsorbed by yeast before the cycle is complete. So while its sickly sweet flavor was once prized as an artificial butter flavor additive and in some brews or wines is tolerated or even encouraged, usually this compound is avoided by American brewers because of its association with underdevelopment and spoilage.

Besides being difficult to produce on a large scale, the extra time the souring process takes, and the inevitable loss of liquid from dumping sours that aren’t good enough for distribution, producing sours requires an enormous investment of equipment and energy.

Sours are very risky because they involve a selective, purposeful contamination that does not play nice with all the other non-sour beers a brewery makes. Often, a full set of separate equipment is required to process and package sours, and any shared equipment requires a great deal of sterilization through heat or chemicals.

After Sanitas’ second annual all-sour day this October, in which everything on tap was a sour, they closed for an entire day and replaced all soft parts in their brewing equipment and every single piece of metal that could not be replaced was cleaned and sanitized thoroughly. This kind of meticulous effort allows Coyne to sleep at night.

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The tap list at the taproom in Boulder for Sanitas’ second annual sour day on Nov. 12, 2016.

At Avery, the same concern persists. If souring organisms got into their packaging equipment and they couldn’t clean it effectively, then they would be making sour everything from that day forward.

“That would be a huge problem and I would lose my job,” Driscoll said.

Avery even de-barrels their sours in a special negative pressure room underneath the bar, so that no bacteria escape into the air in the rest of the facility.

But despite the complexity involved in brewing sours, the opportunity to push and grow the boundaries of brewing beer is ever tempting for home brewers and national producers alike. Events and festivals focused on sour and wild beer can be found across the country, like those hosted by Where The Wild Beers Are, bringing seasoned brewers and amateurs together to taste and swap product. That’s how Oakhold got their very first culture in 2011.

As a recent academic, Levar embraces sharing knowledge so that a community can grow and learn. And as a go-between for microbes and people, he hopes that sours entice an increase in science literacy and accessibility – and bring more curious drinkers to the table.

So while sours are technically nothing new, Levar’s business partner Loesch sees a real opportunity with their scientific expertise, to “add something special to people’s understanding of the broad spectrum of what beer can be.”

But the science of sours isn’t complete without your taste buds. Time to take a risk and experiment.

As Loesch said: “You might be happily surprised.”

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Customers are served at the bar at Avery Brewing’s taproom in Boulder, Colorado.
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