A stout on nitro / Jess Suworoff for DRAFT

As a 19-year-old spending a summer in London, far from parents’ eyes and restrictive laws, I pounded plenty of pints, none more so than Guinness. At my local pub, my bartender would glacially dispense the inky brew, wait for the bubbly waterfall to form a velvety crown and then—only then—top the elixir with one last dark splash. The stout tasted like creamy magic.

The secret, I later discovered, was nitrogen. Most beer is carbonated with carbon dioxide, which creates a sharp effervescence—perfect in a pilsner, not always ideal in a malt-forward beer. For a smoother, creamier, more rounded drinking experience, brewers carbonate beer with a mixture of nitrogen and carbon dioxide (typically at a 70/30 ratio). Typically, low CO2 levels create a beer as flat as hours-old seltzer; nitrogen is insoluble in liquid. The solution is pumping the pressurized brew through a hole-dotted restrictor plate, or sparkler, that both slows the flow of beer and agitates the nitrogen. The tiny bubbles cascade down a glass’s walls and rise through the center, creating a dense head as everlasting as Willy Wonka’s Gobstopper.

Nitrogenated stouts have long been the stock-in-trade of British and Irish pubs. But as the craft market matures, better bars and brewpubs have installed nitro taps and deviated from the Guinness script. Nitrogen turns Deschutes’ roasty, espresso-noted Obsidian Stout—served at the brewery’s Portland taphouse—into rich chocolate milk, while the gas lets Empire Brewing’s golden Cream Ale fulfill its namesake’s promise. (Give it a go at Brooklyn’s Glorietta Baldy.)

Starker yet is nitrogen’s impact on hop-forward ales. When California’s Venice Ale House serves Epic’s piney and pungent Hopulent IPA on nitro, the sharp bitterness is dialed down, creating a bittersweet grapefruit Creamsicle, while Victory’s HopDevil Ale Nitro is a smoother, mellower IPA experience at Chicago’s Fountainhead.

Did you notice the common thread uniting these craft nitros? Drinking them requires you to bend elbows at a bar. At least, that used to be the case. Following the path paved by Guinness, which stuck a nitrogen-filled widget into a can in 1989, aluminum proselytizers Oskar Blues recently released the first widget-fueled craft beer, Old Chub Nitro. Goosed up with nitrogen (and slightly lower in ABV than classic Old Chub), the Scotch ale’s malt profile becomes more multifaceted, allowing drinkers to dive deep into the toffee, smoke, caramel and chocolate from the comfort of their own armchairs.

While widgets are wonderful, Colorado’s Left Hand wanted nothing to do with the plastic tool. Or cans. Instead, the brewery spent two and a half years and hundreds of thousands of dollars dialing in the right gas mix for Milk Stout Nitro. (Naturally, the brewery prefers to keep the process secret; it’s also used for nitro versions of Sawtooth Ale and Wake Up Dead imperial stout.) Released in fall 2011, the milk stout’s pitch-black label bore a peculiar directive: Pour hard.

For me, the command refuted decades of beer drinking, years spent perfecting that 45-degree pour. Intrigued, I bought a six-pack and a roll of paper towels. I uncapped the bottle, turned it upside down and shook out the stout like it was Heinz 57 ketchup. The dark liquid filled the glass, the tiny bubbles forming a head as fat and velvety as anything I was served in London. The stout tasted like my past and the future, rolled into one everlastingly luscious sip.