Beer Fact Friday: Nitro Beer

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The head that seems soft as a down comforter; the bubbles that appear to cascade down the side of the glass, the smooth, creamy body: A well-poured pint of nitrogenated beer is both a feast for the eyes and a treat for the mouth. But what sets nitro beer apart from other pints?

To understand nitro beer, it helps to know a bit about cask-conditioned beer—what British beer-drinkers call “real ale.” Cask-conditioned beer differs from beer served in kegs in that all of its carbonation is a result of fermentation by yeast, which are still alive and active inside the cask when it’s shipped to bars. This natural carbonation results in low CO2 levels and a soft, silky texture. 

It was this texture that St. James’ Gate Brewery, makers of Guinness, set out to recreate. The Irish brewery began developing the technology to mimic the appearance and mouthfeel of cask-conditioned beer using kegs and modern draft systems in 1959. It had perfected the process by the mid-’60s and has been associated with nitro beer ever since. 

Nitrogenated beer differs from standard kegged beer in a few ways. First, nitro beer contains higher nitrogen levels (and lower CO2 levels) than most kegged beers. This changes the requirements for pouring the beer on draft. While most draft systems push beer to the tap using either pure CO2 or a 70/30 blend of CO2 and nitrogen, nitro beers are pushed with a gas blend that favors nitrogen; the blend is usually 70% nitrogen and 30% CO2, and is often called “Guinness Gas.” 

The second piece of technology that sets nitro beer apart is a special faucet that contains a tiny restrictor plate perforated with small holes. As the beer is forced through these holes, the sudden pressure drop from one side of the plate to the other encourages the formation of extremely small nitrogen bubbles. These little guys rise to the top of the glass much more slowly than CO2 bubbles and tend to form a dense, pillowy head of foam that seems as if it could last for hours—and probably could. This longevity is partially the result of our own atmosphere, which is around 80 percent nitrogen. 

Perhaps the most visually stimulating aspect of a nitro beer is the way the bubbles seem to “cascade” toward the bottom of the glass. Friction is the cause of this phenomenon: While bubbles on the sides of the glass have to fight against the resistance of the glass’ surface, the ones in the center rise without any struggle. This creates a small amount of suction, and the bubbles on the side of the glass flow downward to fill the space left by their quickly rising brethren.

Want to try nitro beer for yourself? Our Oatmeal Stout is always on draft at 8th Street and always served via nitrogen. 

Beer Fact Friday is our weekly exploration of the topics that make beer the world’s most interesting beverage. Check back here next week—or follow us on FacebookInstagram, or Twitter—for more fascinating beer trivia. 

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