It seems like just about every brewery today has made at least a minor effort towards aging beers in some type of whiskey barrel. The process, made popular by Goose Island after it released its Bourbon County Brand stout over 20 years ago, has been creeping into brewery offerings with greater frequency ever since, and is finally able to begin to match the consumer demand for these rare and specialty styles.

“It’s about flavor experimentation,” Untappd co-founder Greg Avola says. “People want more and breweries are trying to reach them through these new vessels.”

That sentiment is one San Francisco brewers are finding they agree with.

Tim Sciascia, head brewer at the city’s Cellarmaker Brewing Co., concocted a special make of one of their flagship beers: a Breckenridge Distillery bourbon barrel aged sampling of their popular porter, Coffee and Cigarettes.

“Since [the Bourbon County beer], most brewers have made some type of whiskey, barrel-aged something. We just think it’s a cool thing,” he says. “To come into a brewery and always have that option, people are stoked.”

Another Bay Area brewery, Speakeasy Ales & Lagers, has also been crafting its own line of barrel-aged beers, led by Director of Brewing Kushal Hall. For the last few years, the brewery has selected several of their darker, richer styles, and aged them separately in barrels obtained through a broker, before blending them all in a large Brite tank and bottling as part of their Syndicate series. Their most recent, Syndicate No. 03, is largely comprised of their Scarface Imperial Stout, an espresso and chocolate-forward beer that has become one of their best-loved styles.

“We wanted something really rich, that was distinct enough from our Scarface. Although it’s five stouts, an old ale, and an imperial porter, there’s so much variance, it starts to become something beyond the stout, [and more like] an old ale in flavor,” Hall says. “That’s our goal, to make something unique and unrepeatable.”

However, while the payoff is (literally) very sweet, the process is not without it’s challenges. American whiskey barrels are sparse and are sometimes in bad shape upon receipt, so they can be quite expensive and tedious to use.

“They’re built to only be used once, so they’re not as nicely built as wine barrels,” Hall notes. “There’s a lot more inconsistency in volume, and the staves are a lot rougher, and the oak or char you pick up from one to the next varies a lot as well.”

It’s a challenge most other breweries face as well. While noting his brewery is lucky enough to work directly with a Colorado distillery, Cellarmaker’s Sciascia knows the hustle other brewers have to endure to work with a healthy vessel. “You have to clean the heck out of those barrels,” he says. “If you get a really old barrel, what have you lost? What has it gained in a bad way? Are those positives or negatives?”

Ultimately, though, it seems the final product is well worth the effort. Beers aged in the process gain a new, smoother texture and a slightly oilier mouthfeel, as well as delicate vanillin, subtle oak wood and coconut, and burnt marshmallow notes — depending on what types of whiskey barrels are used.

“There’s impressions you get from the barrel that you can’t taste, [like] that texture, that silkiness,” Sciascia says. “You’re [also] getting a lot of micro-oxygenation over time. You’re changing esters and alcohols into new components so things are combining and mingling and changing over those eight or nine weeks, or months, or years [in the barrel]. That’s just a process of slow aging you can’t get in a fermenter or a keg.”