Sour Union | Craft Beer & Brewing

Sour Union

Wanting an approachable sour beer to offer in the tasting room while longer-term brews matured, brewers at Los Angeles Ale Works developed the Blüme Union fermentation system to ferment a wheat-heavy wort into a briskly tart Berliner weisse in short order.

John M. Verive 1 year, 2 months ago


“Barrels are tough. They’re overly time- and labor-intensive,” says Los Angeles Ale Works (LAAW) Cofounder Kristofor Barnes as he walks among a dozen used wine barrels that fill the empty floor space of his new brewery in Hawthorne, California. Half will be filled with beer for the first time later in the afternoon; the other six have just been emptied and now await the fresh wort that’s finishing a spin in the brewhouse whirlpool. These barrels—four chardonnay barrels, a syrah barrel, and a pinot noir barrel—are part of an interconnected system inspired by the Burton union fermentation system (a fermentation system of interconnected wood barrels that was used predominately by the brewers in and around Burton-on-Trent, England, in the mid-to-late nineteenth century).

Developed to jump-start the brewery’s sour-beer program, the LAAW Blüme Union (named for the Berliner weisse they produce from it) uses a series of manifolds and vinyl hoses to connect each barrel in the three-level tower to a sealed blow-off collection vessel. The barrels are inoculated with a strain of Lactobacillus along with German ale yeast, and the system can ferment the wheat-heavy wort into a briskly tart Berliner weisse in short order.

“The wort goes in the barrel on Saturday, and the beer will be sour by Wednesday,” says LAAW Barrel Director Brian Holter. He says Blüme takes about a month of residency in the union to hit flavor maturity, so while it’s a slower process than the “short cut” of kettle souring, it’s quick for an all oak–fermented beer.


Holter and Barnes hatched the idea for a “Berliner union” while visiting Firestone Walker’s Paso Robles brewery in 2013. “We loved the idea of a union fermentation system, and I told Brian [Holter] to figure out the design,” says Barnes.

Firestone Walker is the only major U.S. brewery operating a union for primary fermentation, but their “Firestone Union” serves a different purpose than the traditional British Burton union fermentation technique popular in the nineteenth century. The Burton-on-Trent brewers prized their system for its efficiency. In the Burton union, froth from beer at high krausen flows from the set of barrels into a trough where yeast at the height of vitality can be captured to re-pitch in the next batch, and the residual beer can recycle back into the barrels.

At Firestone Walker, the beer undergoes a vigorous fermentation for a short time in the barrels before being pushed into stainless-steel tanks. The prize is not just the softer fruity fermentation profile—it’s the spice and vanilla flavors provided by the lightly toasted oak barrels.

“I balked at the idea at first,” says Jeffers Richardson, Firestone Walker’s first brewmaster, “but I have to give David [Walker] and Adam [Firestone] credit for pushing the idea.” Firestone Walker launched brewing operations among the vineyards of the Santa Ynez valley in the mid-nineties, and the founders’ ties to the winemaking industry afforded them a source for new oak barrels.


Walker wanted to tie the new operation to the brewing traditions of his native England, and he took Richardson on a research trip back to the United Kingdom where they visited Marston’s Brewery. “It was a spectacular sight and sound,” says Richardson of the three massive halls containing huge union sets all bubbling vigorously. He returned from the trip excited to make the union work on a smaller scale, and Firestone Walker has used their proprietary set-up for twenty years, primarily when brewing their flagship Double Barrel Ale. Richardson says that the union setup “defies all orthodox brewery systems, and there are all manner of challenges, but we got comfortable with [the union] and now it’s non-negotiable.” The system is ingrained into Firestone Walker’s company culture as an important point of distinction in both flavor and identity.

The Blüme Union

Barnes hopes that the Blüme Union will have a similar effect for Los Angeles Ale Works. “Blüme is a quick way to showcase our barrel and wild side of the brewery,” he says. The brewery opened in February 2017, and while lambic-inspired beers and spirit barrel–aging are on the roadmap, Barnes wanted an approachable sour beer to offer in the tasting room while the long-term brews matured. The light and tart Berliner weisse fit the bill for a few reasons beyond being a perfect style for L.A.’s sunny summers (especially for sipping on the brewery’s patio).

LAAW is the first craft brewery in the city of Hawthorne (a couple of miles inland from the coast and about 12 miles southwest of downtown L.A.), and many visitors to the tasting room are new to craft beer. Blüme offers an accessible yet adventurous flavor for drinkers most familiar with American light lagers.

Blüme is also a blank canvas for further brewer experimentation. LAAW offers a selection of house-made syrups that customers can sweeten their glass with, as is traditional along the banks of the River Spree in Berlin. (Besides the typical raspberry and herbaceous woodruff syrups, LAAW makes everything from peach- to pineapple- to Thai tea–flavored syrups.) There’s also a funky version of Blüme dosed with Brettanomyces, and Barnes enjoys preparing one-off cask-conditioned offerings that showcase locally sourced fruit.

A Lot of Swearing

Putting the union together is simple, but that isn’t to say it’s easy. “The first couple of times, there was a lot of swearing,” says Barnes. After racking finished beer from the union set of barrels into a blending tank, they transfer fresh Blüme wort in on top of the sediment from the previous batch. This robust colony of Lactobacillus and a strain of Kölsch yeast chosen for its acid tolerance kick off fermentation in a matter of hours. With a deft touch on the forklift, Barnes stacks the filled barrels, and Holter begins assembling “the apparatus”—the series of manifolds and hoses that connect the barrels together. This is where most of the swearing happens as the brewers wrestle to get the connections in place before they connect the output of the union to the stainless-steel 10-gallon cylindroconical fermentor that will capture the blowoff. Holter will harvest yeast from this vessel to re-pitch into the next batch of Blüme, and the closed-loop system protects against acetobacter contamination.

The Blüme recipe is traditional except for the notable addition of spelt malt to a grist of malted wheat and Pils malt. The spelt is there to bolster the malt flavor and aid in head retention, and just enough hops are added to the whirlpool to increase complexity without impeding the Lactobacillus with too many IBUs. The wort is brewed to about 9° Plato, and it finishes well below 2° Plato at about 3.5 percent alcohol.

While there’s some oak character in the final product, the barrels’ true impact is in the way the beer ferments. As with the Firestone Walker Union, the geometry of the barrels and the slight pressure that the system is under help the yeast (and here, bacteria) to thrive, affecting the fermentation in subtle ways. The beer is brightly acidic, but not sharp; complementary esters round off the edges; and a mild hops character helps balance the tartness.


Engaging Customers

“There’s a romance to using oak,” says Barnes, “and Blüme is a great way to engage with customers.” Cofounder Andrew Fowler adds, “One of the unexpected returns of our union system is all the questions customers ask about it!” Every customer interaction is an opportunity for the LAAW team to share their passion for beer, and the tower of barrels bubbling beer through the connected hoses is a striking sight in the tasting room. It’s a favorite stop on ad-hoc brewery tours. “Questions lead to discussions, and discussions lead to education,” Fowler says.

The barrel union system, like the brewery itself, is young and constantly developing. Holter and Barnes aren’t sure how many uses they’ll get from the original six barrels or how the Lactobacillus culture will evolve with each turn. Will this autumn’s Blüme taste notably different from the initial spring batches?

The LAAW team is driven to experiment, and they credit their homebrewing experience for their approach to brewing at scale. “We are all homebrewers,” Barnes says proudly. Holter adds, “it feels like there’s a stigma around homebrewers turning pro, but we reject that. We celebrate our homebrew roots.” There’s no fear of failure in the bunch, just a fear of getting too comfortable.