London: Scientists have explained why tapping a newly-opened beer bottle quickly turns booze into foam.
Researchers from Carlos III University in Madrid, Spain and Universite Pierre et Marie Curie, Institut Jean le Rond d`Alembert, France, have shed new insight into the science behind foaming beer bottles by exploring the phenomenon of cavitation.
Cavitation, a phenomenon relevant to common engineering concerns such as erosion of ship propellers, is the mechanism by which bubbles appear in a liquid such as beer after an impact, said Javier Rodriguez-Rodriguez, the lead researcher from Carlos III University.
After a sudden impact against a bottle`s mouth, back and forth movement of compression and expansion waves will cause bubbles to appear and quickly collapse.
The team`s investigation of beer bottle-fluid interactions demonstrated that the cavitation-induced break-up of larger "mother" bubbles creates clouds of very small carbonic gas "daughter bubbles," which grow and expand much faster than the larger mother-bubbles from which they split.
The rapid expansion of these daughter bubbles gives the foam buoyancy.
"Buoyancy leads to the formation of plumes full of bubbles, whose shape resembles very much the mushrooms seen after powerful explosions," Rodriguez-Rodriguez explained.
"And here is what really makes the formation of foam so explosive: the larger the bubbles get, the faster they rise, and the other way around," he said.
He added that this is because fast-moving bubbles entrain more carbonic gas.
The study is believed to be the first quantitative analysis of the beer bottle foam-over.
The findings will be presented to a meeting of the American Physical Society (APS) Division of Fluid Dynamics in Pittsburgh.