Learn in Beer, Bubbles and Cellulose

As St. Patrick's Day draws near, many of you may be anticipating a nice chilled glass of Guinness, complete with a creamy foam head. But if you're not propping up a bar in Ireland, and are instead pouring your beer out of a can at home, that long-lasting head can only be produced with the help of a plastic widget.

Simply pouring a carbonated beer, such as a lager, from the can into a glass is enough to generate a head. But this is not the case for stouts, which are infused with nitrogen bubbles, rather than carbon dioxide, in order to create their uniquely smooth texture. The small plastic widgets in each can of stout contain pressurized nitrogen, which is released once the can is opened, triggering some of the dissolved nitrogen in the beer to bubble up into a head.

Using applied mathematics, including the ideal gas equation and a fourth-order Runge-Kutta scheme with a timestep of 10-3, however, a team from the University of Limerick in Ireland recently discovered that microscopic plant fibers made of cellulose, such as cotton, can also froth up a stout.

In a paper publishing their findings earlier this month, the Limerick mathematicians conclude:

A typical pouring time for a stout beer is 30 seconds. In this time about 108 postcritical nuclei must be released. A single fibre produces one bubble every 1.28 seconds. Therefore about 4.3 × 106 fibres are needed. If each fibre occupies a surface of area λ2 then the total area that must be occupied by fibres is 8.3 × 10-4 m2.

Or, in plain English, embedding a 1 inch square of food-safe biodegradable cellulose fibers in a Guinness can would produce a perfect creamy head, doing away with the need for plastic widgets altogether. And although the technology is a long away from the shelves yet, removing plastic from our food chain is certainly something to drink to.

Images: Thumbnail (cc) by Flickr user raygunb (1) Courtesy of Michael Devereux/Mathematics Applications Consortium for Science and Industry, via Wired, still showing how pockets of air trapped in tiny cellulose fibers, each between 10 and 50 microns wide, help nitrogen and carbon dioxide bubble out; (2) the Guinness widget (cc) by Flickr user slworking2, via Wired.

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