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.
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