The Science Behind Nitro Beer

“Nitrogen is very insoluble in liquid,†Cain states. “To get it to dissolve, you need to pressurize it, and you need to keep it cold.â€

So, to serve nitro beer on draft, you need pressure. Nitro beers are nitrogenated either before packaging in pressure-sealed kegs or in-line on the way to a draft system. Dedicated nitro drafts feature a restrictor plate, forcing the beer through tiny holes and allowing the dissolved N2 gas in the beer to escape quickly. This creates a stunning cascade effect that forms immediately in the glass.

If you’ve ordered a nitro beer, you’ll likely recall that whirlpool effect—tiny bubbles dancing in a typhoon of a creamy dark stout. Because the glass is not pressurized or cold enough, nitrogen is trying to escape. And, the fastest way out is down. So, nitrogen rushes down, fluffy, fragrant foam forms up top, and then nitrogen escapes up and out the sides of your glass. It’s a stunning visual effect that leaves you with a glass of frothy beer.

To recreate that experience in a packaged product, Guinness placed a widget in its bottles and cans. When Guinness infused liquid nitrogen into its stout while packaging, nitrogen rushed into the widget and stayed relatively well-pressurized. But, when you open that can of Guinness, pressure drops, and the nitrogen escapes from the widget. (You’ll likely hear a pop when you open a nitro beer.) And, with a hard pour, you can create that swirling nitro beer effect as the nitrogen dances down and out of your glass.

Over the years, liquid nitrogen dosing has improved, so the widget isn’t necessary for packaged beers. In fact, folks like James Cain at Chart Industries helped to develop dosing techniques that create a more precise packaged product. Brewers can simply dose their beer on the packaging line without needing a widget. Consumers pop open the beer, “hard pour†their beer, and, voila, lush nitro beer in a glass.