In my latest article for The Bulletin this week, I embrace the St. Patrick’s Day theme and talk about nitro beers—or, more accurately, about nitrogenation as opposed to carbonation and how it works in beer.

For many, the defining characteristic of Guinness is its creamy, silky texture and dense, thick head of foam, intimately familiar to anyone who has witnessed the ritual of a draft pour of the stout.

As the beer is poured into the glass, the foam piles up immediately, seeming to dominate the pour.

The brown-black liquid swirls and undulates as it gradually separates from the cream-colored head, similar to an ice cream float, and tiny bubbles appear to cascade down, not up, the inside of the glass. This process can take a minute or more.

Beer might range in carbonation levels from flat to fizzy, but most beers don’t approach this level of creaminess. So what gives Guinness its luscious look and feel? The answer is nitrogenation.

I go into more details and the science of nitrogenated beer, and offer up some local suggestions for nitro beers that are pouring now (or, were when I turned in the article last weekend). So if you’re looking for a nitro-alternative to Guinness for St. Paddy’s, you might find some ideas here.