Barrel-aged sour beers are a rather new phenomenon in the United States — most are less than a decade old — although they’ve been made for centuries in Europe and elsewhere. It’s a traditional practice that began before other, more modern fermentation vessels and carefully created yeasts were developed. Today, many U.S. beer producers are aging some of their most exotic brews in casks with the aim of producing a beverage as nuanced as barrel-aged wine can be.

In the modern era, many people credit Vinnie Cilurzo of Russian River Brewing in Santa Rosa, Calif., with being one of the first in the United States to seriously investigate and popularize this brew category. It’s a style that’s definitely not for everyone, though it does offer a creative (if challenging) alternative to even the most esoteric of beers and ales. It’s also among the most unusual forms of microbrew experimentation.


The Rare Barrel’s Alex Wallash says sour beer is “more like wine, cider, [sparkling wine], or even lemonade.”

An Acquired Taste

Traditional American lagers, typically refreshing and delicate, can be seen as a completely different product when compared with microbrews such as IPAs. Barrel-aged beers and ales are even more esoteric and odd. Alex Wallash of The Rare Barrel in Berkeley, Calif., whose entire production is dedicated to barrel-aged sour beers, explains the product: “If you’re new to sour beer, forget what you think beer is,” he says. “It’s more like wine, cider, [sparkling wine] or even lemonade. It’s very different from any other beer style.

“Here at Rare Barrel, we talk about the three-sip rule. The first sip is shocking because the beer is so tart and acidic. With the second sip, you start getting used to it — but you know this isn’t like anything you’ve tasted before. By the third sip, you’re cruisin’.”

Most whom avidly support sour beer say they’re not to be quaffed quickly but rather sipped slowly. Almost always, they’re consumed from a glass — never from a can or bottle — to appreciate the aroma and open the flavors. Wallash cautions that, for many newcomers to sour beer, it’s an acquired taste. “For example, stout has familiar flavors that are like coffee or a chocolate bar,” he says, “but sour beer has flavors that are hard to find in other foods.”

He adds, “The category is taking off because of brewers like Vinnie [Cilurzo], who are pioneering the idea. But its growth is slower than a traditional IPA, because it takes a lot of work and time, so production of these beers is usually limited.”

Rare Barrel’s best seller, Ensorcelled, is aged in-barrel for a full year (first fermentation with Brettanomyces yeast (commonly referred to as Brett) and Lactobacillus bacteria; second with 40 pounds of raspberries) added, but, says Wallash, “you can make an IPA in a few days.” The company is currently sold out of Ensorcelled and is months away from the next release.


Complicated Production

Brewers say aging beer in a barrel must be undertaken with extreme care, partially because of the expense involved, but also because the end product could turn out to be so rarefied that the potential clientele is pretty much unknown. On the flip side, since brewers who produce sour beers with aplomb can usually charge more for them, many craft breweries are delving into this relatively new category.

So far, the sour beer phenomenon is considered a niche product, and very few larger brewing companies have gotten into the game because the potential market is seen as small (basically limited to beer enthusiasts willing to pay more for a beer that some view as odd).

Russian River Brewing’s Vinnie Cilurzo is considered by many to be at the front of a sour beer revival in the United States.

Cilurzo says the growing sour beer phenomenon is mostly driven by dedicated beer enthusiasts. He explains that these beers can be a little challenging to beer newcomers, since they can be so different not only from traditional beer, but also batch-to-batch. In a sense, they’re a bit like the different vintages of wine. Such variations are well understood by wine lovers, who accept vintage variations as normal. Likewise, variations in sour beers don’t seem to puzzle beer aficionados.

Such variations are commonplace when wild and erratic yeast strains such as Brett or Lactobacillus bacteria are employed to generate the required flavor characteristics. One agent, Pediococcus, is considered so pernicious in the wine business that any wine with even a trace of it is considered infected and the wine is scrapped. In contrast, Pediococcus is consciously employed by some beer makers for an added note of complexity (it doesn’t produce the same elements as in wine).


Worth the Trouble

Alec Klassen, a sales associate at The Beverage People, a home fermentation supplies purveyor in Santa Rosa, Calif., says sour beer aged in barrels “is the premium end of the market right now for beer.

“It’s a more difficult process to make sour beer and it entails much more risk, because you never have full control over the fermentation,” adds Klassen, a brewer who has a degree in food science from Oregon State University. “Producing well-made sour beers can build notoriety or ‘street cred’ among a discerning consumer base, which can translate to higher sales of a brewer’s conventional products.”

According to Klassen, it takes an educated brewer to understand what’s going on during the fermentation process, and making sour beers at a small or underfunded craft brewing company can be extremely tricky. “A lot of new craft breweries are started by less experienced brewers, and many of them want a sure-fire way to make beer that will sell. That’s not easy with sour beer. You’re using multiple strains of yeasts and bacteria, all of which grow in different ways and can create pretty complicated fermentations.”

“The risk [with many yeasts] is there, and the best bet is to quarantine the equipment.” He continues, “Brett is a slow but very durable grower, and it takes a lot to knock it back. It doesn’t produce that much acid, but it does create a rustic, barnyard character” that characterizes many premium sour beers. Though it can be very tricky to deal with in a winery, it’s seen as a positive element in creating sour beers.

The risk of cross-contamination is high, says Cilurzo. “When brewing sour or funky barrel-aged beer using Brett, Lactobacillus and Pediococcus, there’s a high risk of cross contamination with the clean, non-funky beers in our portfolio,” he explains. “These wild yeasts and bacteria can easily take hold, so extreme care must be taken to ensure they don’t get in the regular beer.

“To that end, we have all separate equipment when making the funky beer. That means we have at least two of everything — a clean set for our non-funky beer and a second set that we only use for our funky beer.”

He’s about to go one step further: “Soon we will be breaking ground on a new brewing facility, where we’ll isolate the sour/funky beer production to a specific part of the building, so there will be no comingling of our non-funky and funky beer.”

Firestone Walker Master Blender Jim Crooks says, “We’re fortunate to use freshly emptied barrels from renowned wine producers.”

California’s Firestone Walker has already built a separate facility in which to make its sour brews. Says Master Blender Jim Crooks, “By design, our Barrelworks was created in Buellton, while the main production facility sits in Paso Robles. The threat of cross contamination between facilities is minimized by this distance. We never send anything back to the Paso Robles facility that contains active cultures that could have any potential to be mistakenly introduced into that facility. We only send finished and packaged Barrelworks beer back to Paso.”

Like RRB, Firestone Walker relies on relationships with local wineries to source 90% of the barrels it uses. “We’re fortunate to use freshly emptied barrels from renowned wine producers like Booker Vineyard & Winery, Saxum Vineyards and Wild Horse Vineyards,” says Crooks.


Minimizing Cross-contamination

According to Klassen, “Unless a brewer has an education in fermentation science and understands the way these wild yeasts and bacteria operate, “the beer could be radically different from batch to batch — or turn out to be unsalable.

“Improper pairing of bacteria and yeast strains can lead to fermentation problems,” he explains. “For example, a Pediococcus fermentation produces desirable lactic acid but can produce slimy polysaccharides, which ruin mouthfeel. Brett can break down these polysaccharides and so is introduced after a Pediococcus fermentation to restore a pleasant texture to the beer.”

One solution to the problem is to have different vessels for each fermentation, since once a barrel is used with Brettanomyces yeast, it can’t be used for any other kind of beer.

FW’s Crooks says, “We’re constantly striving to understand the biochemistry behind the flavors being produced by our myriad bacteria and wild yeast. Explaining how to control or promote some of the flavors we’re getting from the Lactobacillus bacteria would just be us guessing.

“For now, we have a method and we try to be consistent — or relatively consistent — with our approach. Sometimes, what you think is a minor change in a recipe or treatment liberates a wildly unexpected result. It’s these results that send us back to the books or beer blogs looking for scientific explanation for the unexpected flavors or aromas. It’s a continual learning process.”


Leading the Way

Cilurzo points out that the slight variations in sour beers from one batch to another actually intrigues most beer lovers. (By contrast, in the early 1980s, Budweiser staged a major national promotional campaign to emphasize the absolute consistency of its beers from its various breweries around the United States.)

Russian River Brewing Co. makes several beers that are aged in barrel, including Temptation, Supplication and Consecration, which use barrels that are three to five years old. “The idea isn’t to get a lot of oak flavor,” says Cilurzo. “Supplication is built around cherries,” for example, and for Consecration (aged in used Cabernet Sauvignon barrels), “we’re looking for more Cabernet flavor, but not the tannin.”

These beers are also not a product of assertive hops or malt. Rather, it’s the aging process and contact with wild yeasts and bacteria that give these brews their unique characteristics. Cilurzo has 600 barrels in use at his Santa Rosa brewery and will have 1,500 in his new production facility in nearby Windsor (opening in 2018).

It’s easy to understand why new, aged-in-barrel beers aren’t developed very quickly. Much experimentation is needed to determine precisely which yeasts, barrels and fruits are compatible, which all takes not only a lot of time but also a lot of expense. When such a project is undertaken, the result could well turn out to be a failure, leaving the brewer with a product that had zero profit potential.

Many craft breweries around the United States have experimented with barrels, and some of the results have developed strong regional or local followings. Many, however, seem willing to hang back and let their more adventurous colleagues take the lead.

(If you’re intrigued by the beers mentioned in this story, here are more to seek out.)