Making a monster sour

River City's TW Frankensour (right), and the now 19-year-old beer that inspired it.

Barrel-aged sours typically take a year or more to mature, but the new one from River City has been in the works for close to 20.

The downtown brewery on Friday unveils its TW Frankensour, assembled Frankenstein-style from the remnants of four different beers – one dating back to 1996, from River City’s predecessor, Coeur d’Alene Brewing.

(Some background: Before Coeur d’Alene Brewing was bought in 1999 by the family that later launched River City, it operated under the T.W. Fisher’s brand name, after its founder. It closed in 2010, but River City continues to make one of its more popular products, a huckleberry ale.)

The Frankensour story starts in August 2013, when the Inland Brewers Unite homebrew club held a gathering at Twilight Cider Works on Green Bluff. Twilight owner Will Jordan’s father-in-law formerly ran a beverage distributorship out of the building, and as the evening went on Jordan pulled out some old beer kegs for the group to sample.

Homebrewer Harry Lawrence, a friend of River City brewer Moose Sanders, took one taste of 1996-vintage T.W. Fisher’s huckleberry – which had soured naturally in the keg – and bought it on the spot.

“I handed him $50, told him to take it off the tap and took it home,” Lawrence says.

Lawrence didn’t tap the keg again until last August, to celebrate earning his physician’s assistant degree. He took a growler in for the River City crew to try.

“It’s not that often you come across a beer that’s 18 years old, and if you do, to have it taste that awesome,” Sanders says.

Sanders, meanwhile, had recently finished aging some of River City’s huckleberry ale in a Barrister Winery cabernet franc barrel. After kegging that beer, he filled the empty – and increasingly funky – barrel with some leftovers of an experimental India pale lager (actually brewed with both ale and lager yeasts).

Then, in a true mad scientist move, he tossed in the dregs of Lawrence’s growler to kickstart the souring. Nine months later, the barrel beer was mellowed by blending with River City’s Girlfriend Golden, and TW Frankensour was born.

“It will never be replicated, I’m telling you that,” Sanders says.

He and Lawrence were kind enough to share an advance sample of the finished Frankensour, along with some of the final remains from that 1996 keg. Each was a delight, in different ways.

The older beer was surprisingly crisp, its bright, berry-tinged tartness accented with mineral-like notes. Its offspring was richer and fuller, with a funky, earthy character balanced by an underlying sweetness.

You can taste the Frankensour for yourself when River City opens tomorrow at 3. Only one keg has been set aside for the taproom, so it will be served in 8-ounce pours at regular pint prices.

Another keg is reserved for the Inland Northwest Craft Beer Festival at Avista Stadium on Oct. 2-3. The rest is being sold to outside accounts, including Manito Tap House and The Blackbird.

And some of another version of the blend is tucked away in River City’s cellar, awaiting whatever fevered inspiration might strike in the future. Bride of Frankensour, anyone?