Irish mathematicians have discovered tiny plant fibers can make nitrogen bubbles out of stout beer and form a creamy head of foam. The find could mean an end to more expensive and less-eco-friendly technology currently used to create fizz.

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.”

Carbon dioxide dissolves into beer during the brewing process, and the gas quickly nucleates to form bubbles in the liquid with the help of special surfaces. Microscopic plant fibers that hide in drinking glasses are especially good at bubbling up carbon dioxide because they trap small air bubbles that make for excellent nucleation sites. But carbonated brews form large, fragile bubbles and heads that quickly fizzle out.

To create longer-lasting and creamier heads in stouts, brewers pump the beer full of nitrogen because the gas forms smaller, more stable bubbles without affecting taste. A tiny opening in the nitro bartaps forces nitrogen into stouts as the beer is poured, but canned stouts are trickier because plant fibers don’t help nitrogen bubble out. Or, so beer experts thought.

Lee and his team recorded stouts under a microscope (video above) to watch bubbles form inside cellulose fibers. They discovered the bubbling rate was up to 20 times slower than in carbonated brews, which is probably why no one had noticed it before.

“If you line a can with enough of them, you can get a creamy head in less than 30 seconds,” Lee said, roughly the time it takes to open and pour a stout.

It takes roughly 4.3 million microscopic fibers to accomplish the feat, which translates to a postage-stamp-sized pad of fibers. Food-safe cellulose should be cheaper than widgets to put into cans, Lee said, especially since the latter require a de-oxygenation process to prevent spoiling the beer.

Lee and his team hopes their discovery will make stouts slightly cheaper (on the order of a few cents per can), in addition to creating new research leads in fluid mechanics.

Video: Pockets of air trapped in tiny cellulose fibers, each between 10 and 50 microns wide, help nitrogen and carbon dioxide bubble out. Courtesy of Michael Devereux/Mathematics Applications Consortium for Science and Industry

Image: A plastic widget found in a can of Guinness stout beer. slworking2/Flickr

Via Technology Review



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