Posted on 28-12-2003

Hard-to-swallow tale of beer antibubbles

Belgian scientists have put a different kind of fizz into physics. They have studied that fleeting mystery of the foaming tankard - the antibubble.
Antibubbles can move down the glass. If a bubble in air is a thin film of liquid that encloses a pocket of air, an antibubble is a thin film of air made inside a liquid, enclosing a pocket of liquid.

Stephane Dorbolo and colleagues at the University of Liège and the Collège de France report online today in the New Journal of Physics that they had found out how to create antibubbles in a variety of liquids, including water dosed with washing up liquid.

They repeated the phenomenon in a glass of Belgian beer, thus confirming, according to the Institute of Physics in London, joint publisher of the journal, "what British real ale drinkers have claimed for a long time: that Belgian beer actually is a lot like dishwater".

The research is yet another demonstration of very domestic science: in the past few years physicists have examined why biscuits crumble; which biscuits are best for dunking; how to make a perfect cup of tea (yes, put the milk in first); why a film forms on a cooling cuppa; how to improve a golf swing and, only last week, the equation for a perfect roast turkey.

Antibubbles can be made by pouring a liquid containing a surfactant (think of soapy water) into yet more liquid containing a surfactant. The rate at which the liquid is poured is critical. At the right speed, antibubbles form because a thin film of air is sometimes pulled down with the liquid.

Antibubbles cannot be made in pure water, pure alcohol or pure oil. But they can be made in beer, which contains a protein that acts as a surfactant.

"We tried to create them in beer for fun, and didn't think it would be possible, but were amazed when we managed to create giant antibubbles which lasted for almost two minutes and that moved around a glass of beer before bursting," Dr Dorbolo said.