Barrel-aged cocktails are bringing complexity and nuance to US bar drinks.

When Chris Tucker looked around for ways to challenge himself, try new things and elevate his game as bar manager at Hook & Ladder in Sacramento, he decided to start making cocktails in wood barrels.

While a few people had experimented with the process elsewhere in the United States, it was still relatively uncharted territory.

Add the ingredients, stir them up, seal the lid and walk away – often for as long as eight weeks.

What happens to a martini sitting in the dark, kissing the dense oak of a Hudson Baby Bourbon barrel for that long? Or a Bijou (French for “jewel”) with Plymouth gin, green chartreuse, vermouth and orange bitters?

Tucker is finding that the ingredients meld and mingle and express themselves in bright yet subtle ways, with potential rough edges smoothed, the heat of the alcohol muted to the point that at first it drank as if it lacked heft.

And he’s serving these barrel-aged creations in an ongoing rotating series to rave reviews. We recently visited the midtown restaurant and bar for a taste of the Bijou and found the drink to possess a near magical melding of flavours, soft and soothing with plenty of depth.

Tucker, who began the series with a classic martini (gin, vermouth, orange bitters), has learnt plenty about what happens – and what doesn’t – through barrel ageing.

All of these drinks are served as draft cocktails, much the way draft beer is poured.

“By ageing, … the flavour is fantastic,” Tucker says. “You get this mellowing process. Something fun and magical happens.

“The ingredients get time to play and find a way to exist together. It takes on spice and flavour and a hint of bourbon quality.”

More and more, craft beer makers have been ageing some styles of their brews in barrels to impart additional flavour notes and complexity. It is one of the hottest boutique categories of the craft beer boom.

With cocktails, ageing has likely been going on for decades, if not centuries, in some fashion. In the United Kingdom, some bartenders age their cocktails in glass or steel containers, though the process tends to be longer and more subtle.

The American credited with leading the recent trend of using oak barrels is Jeffrey Morgenthaler, the bar manager (with a physics degree) at Clyde Common, a gastropub in Portland, Oregon.

Tucker has done plenty of research, including corresponding with a chemist and cocktail enthusiast in Toronto, Darcy O’Neil, author of the popular Art Of Drink blog.

O’Neil figures barrel-aged cocktails “are essentially oxidised cocktails”. He goes on to note that oxidation converts some of the alcohol to acetyl-aldehyde, which can suggest flavours like green apple, grass or nutty. The barrels can impart vanilla and oakey notes.

With all this and the smoothness that comes with ageing, barmen like Tucker are serving a nuanced cocktail that aficionados are raving about. Up next at Hook & Ladder is a barrel-aged Martinez, which many say is the precursor to the modern-day martini.

“The response has been amazing,” Tucker says.

But that kind of enthusiasm means there is pressure to keep up the supply. While it takes six to nine weeks to age a cocktail in the 19-litre gallon barrel, the drink lasts only two to three weeks in the draft system, meaning there were weeks when Tucker was unable to serve his new potions. The recent addition of two oak barrels should solve that.

With the maiden martini effort, Tucker first was taken aback – it tasted as if he had skimped on alcohol.

“We found that after six weeks, the cocktail was too smooth, too mellow. I had to adjust my portions, add more gin and let it age another two weeks before I could serve it,” he says.