The Physics of Stout Foam

Did you know that the foam on a can of Guinness comes from a widget? It's a ball of nitrogen that is released into the stout when the can is opened. Now that you know, widgets may be on the way out.

Nitrogen-infused stouts are known for their long-lasting and creamy heads, a feature that carbonated beers can’t emulate. But nitrogen doesn’t froth up on its own, so to get foam on a canned stout, brewers insert a widget — a small plastic ball with a hole in it. When a can is opened, the widget releases pressurized nitrogen into the beer, which then triggers more dissolved nitrogen in the beer to bubble out.

But a graduate student supervised by applied mathematician William Lee at the University of Limerick in Ireland discovered that microscopic plant fibers made of cellulose, such as cotton, can also froth up a stout.

“What happens around these fibers is really complex, so it’s a ripe area for research,” said Lee, who posted his team’s research March 2 on arXiv.org. “This is also a matter of national pride. Stout beers are as culturally important to Ireland as champagne is to France.”

The equivalent of a postage-stamp piece of a coffee filter attached to the inside of the can would do the trick, making canned stout both cheaper and more environmentally-friendly. Link -via Discoblog