Tuesday, March 8, 2011

The ugly truth, long known, is finally spoken.

bubble of beer on a bottleImage via Wikipedia
Many a beer drinker will have puzzled over the following: why, when a can of beer is opened, do carbon dioxide bubbles form so slowly. Why not all at once?

The study of bubble formation in carbonated drinks is a relatively new science. In fact, it is only ten years since scientists settled this matter. One group calculated from first principles the rate at which carbon dioxide leaks from solution into a bubble. The answer is slowly. What's more, it cannot start start without some sort of nucleation site.

Then, another group discovered that the primary sources of nucleation are pockets of gas trapped in cellulose fibres in the drink. The news was greeted by the sound of clinking glasses the world over. Problem solved, right?.

Not quite. While most beers and lagers are pressurised with carbon dioxide, some stouts, dark beers such as Guinness, are pressurised by a mixture of carbon dioxide and nitrogen.

They do this because nitrogen forms smaller bubbles giving the drink a smoother, creamier mouth feel. But it also changes the bubble dynamics significantly. The question is why.

Today, William Lee a mathematician at the University of Limerick in Ireland and a few pals extend the theory of bubble formation to include nitrogen in the mix. Sure enough, nitrogen leaks out of solution more slowly ensuring that its bubbles are smaller. No surprise there.

But Lee and co's formulation of the problem leads to an interesting idea--the possibility of an entirely new type of widget.

If you're not familiar with widgets, here's some background. One problem with nitrogen-pressurised stouts sold in cans is that opening the can, depressurising the beer and pouring it into a glass does not create enough bubbles to form a head. {Read on}