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Chris Drosner writes the Beer Baron column for the Wisconsin State Journal.

O'so Infectious Groove, Liquid Soul

O’so Brewing of Plover last month debuted two new beers: Infectious Groove, a Berliner weisse, left, and Liquid Soul imperial stout.

To kick off 2016, O’so Brewing has released two new beers on absolute opposite ends of the spectrum: dark, forbidding and mysterious; and light, crisp and tart.

Both the year-round Berliner weisse Infectious Groove and winter seasonal imperial stout Liquid Soul come from style families the Plover brewery has excelled at, and the terrific tandem is a welcome return to form after a turbulent year.

As did most craft breweries, O’so grew last year, boosting production 18 percent to about 6,000 barrels. But the company had to rename its signature dark beer, Night Train, under trademark duress. After fielding hundreds of suggestions from fans for a new name, the simple and clever “Night Rain” won out.

Far more damaging, though, was a series of quality problems besetting the big and barrel-aged beers that were the stars of O’so’s seventh anniversary party in November 2014. On tap, the beers sold at the party were outstanding, but the beer inside the bottles sold that night was woefully undercarbonated — a problem O’so founder Marc Buttera ascribed to yeast that just couldn’t produce any more bubbles at the 13 percent-plus ABV liquid it was being asked to ferment in.

I eventually found that a 12-ounce bottle of Night Train provided enough carbonation to salvage a 750-milliliter bottle of its bourbon barrel-aged big brother, but at $20 a bottle that’s mixology that shouldn’t need to happen.

Worse, some of the barrel-aged beers from the seventh anniversary bottle release and other barrel-aged releases earlier last year were loaded with off flavors. Buttera said that problem may have been caused by a faulty piece of equipment that was retaining liquid and causing infection.

The problems turned off some of the beer geek crowd — the discerning audience O’so’s entire barrel and sour program is made for — and caused a lot of soul-searching and refinement of processes at the brewery.

“It humbles you,” Buttera said. “People expect you to be great, they want you to be great. They want another great Wisconsin brewery, and they want it to be you.”

The good news is O’so is unquestionably back on track. I rang in the new year with Arbre Qui Donne, a peach sour that unquestionably would have been one of my beers of the year if I’d popped the cork early enough.

The winning streak continues with the two new, far more plentiful beers.

“It’s getting to the point where our brewery — it’ll be 8 now — it gets tougher and tougher to really knock people out with something,” Buttera said. “It’s a fight to try to stay relevant even though you’re making great stuff. You really gotta crank one out of the park to get noticed, and hopefully that’s what we’re doing with this stuff.”

Infectious Groove

Buttera and his team have already left their mark on the Wisconsin sour beer landscape with previous releases, but Infectious Groove represents a huge leap: it’s the first year-round six-pack sour beer.

To make that possible, O’so used a relatively new technique called kettle souring, a far faster and cheaper way of making sour beer.

Most traditional sours pick up the bacteria and wild yeasts that give them their trademark acidic tartness or funk through aging in wooden barrels. These are the lambics, gueuzes and Flanders reds you find hailing from Belgium, New Glarus and Madison’s own Funk Factory Geuzeria. When properly made, these beers host a party of microorganisms that give them world-renowned depth and complexity.

In addition to the time it takes, traditional sours are somewhat risky to standard breweries. If those bugs get into beer they’re not supposed to be in — and they’re shifty little critters — entire batches of pale ale, pilsner or stout can be lost. For that reason many breweries keep sour production completely separate.

Kettle souring involves briefly cooking a mash — a mixture of milled grain and water — before letting it cool and dosing it with lactobacillus bacteria. After usually a couple of days, the bacteria will have done its job of producing the acidic tartness and the brew kettle will be fired back up to finish cooking. Importantly, those high temperatures also kill the bacteria in the brew kettle, clearing the way for subsequent “clean” batches.

The sour effect produced by kettle souring is generally less intense and complex than traditional sours, but it works nicely for many beers, including the Berliner weisse wheat ale that Infectious Groove is based on. And it’s essential if you want to get thousands of bottles of a sour into the market.

“Our hope is this: That’s our refrigerator beer for the beer geek,” Buttera said.

Infectious Groove pours a gently fizzy pale yellow — far lighter carbonation than you’d get from a traditional Berliner — with a slightly musty, moderately sour aroma. That tartness, however, explodes on the palate with an intensity usually seen from barrel-born sours, albeit briefly before receding in a clean, refreshing finish.

Despite the December debut, this beer is going to be in my fridge a lot when the weather heats up.

The basics: Replaces Memory Lane pilsner as year-round offering, $8-$9 per six-pack, 4.8 percent ABV.

Bottom line: 4 stars (out of 5)

Liquid Soul

This brawny imperial stout traces some of its lineage up the road at another accomplished Central Wisconsin brewery that, like O’so, knows a thing or two about big black beers.

Brewer Mark Spilker joined O’so in fall 2014 after four years at Central Waters, and when the O’so team decided to go with an imperial stout for a new winter seasonal, Buttera tapped Spilker.

“’I don’t want a Central Waters beer, I want a Mark Spilker beer,’” Buttera said he told him. “He definitely put his touch on O’so there.”

Spilker’s creation replaced the seasonal Dank imperial red and was dubbed Liquid Soul, an also-ran name submitted during the Night Train renaming contest.

It pours a slightly darker black, with a nose of molasses, chocolatey malt and a prominent note of hot alcohol as well. Flavor follows, with the chocolate coming into the forefront along with a deeper coffee-like roasted character that runs the finish. Full, warming and complex, Liquid Soul is a showcase for what a great imperial stout can be.

I was barely halfway through my first glass before thinking how good Liquid Soul could be out of a bourbon barrel. Buttera had the same thought, and while it’s not aging yet pending the purchase of more barrels, he does intend to make barrel-aged Liquid Soul a thing.

The basics: About $10 per four-pack, 9.2 percent ABV.

Bottom line: 4 stars (out of 5)

Got a beer you’d like the Beer Baron to pop the cap on? Contact Chris Drosner at or follow him on Twitter @WSJbeerbaron.