Ever had your beer bottle "tapped," only to have it foam and overflow? European researchers finally let us on on the science behind the party gag.

It’s everyone’s most or least favorite party gag, depending on who’s on the receiving end: Someone takes their beer bottle, and when the opportunity presents itself, gently “taps” its bottom on the open mouth of their victim’s bottle. The result is a foaming, overflowing beverage, a ruined beer and a harshed buzz. Most people are too preoccupied with the ensuing mess to give much thought to the physics at work in the background. Fortunately, researchers from Carlos III University in Madrid, Spain and Universite Pierre et Marie Curie, Institut Jean le Rond d’Alembert, France are not most people. They looked into the phenomenon, and presented their explanation at the annual meeting of the American Physical Society (APS) Division of Fluid Dynamics on Sunday

It turns out that Cavitation, a phenomenon relevant to such common engineering concerns 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 adds that this is because fast-moving bubbles entrain more carbonic gas.

The team’s work is believed to be the first quantitative analysis of the beer bottle foamover. “We wanted to explain the extremely high efficiency of the degasification process that occurs in a beer bottle within the first few seconds after the impact,” Rodriguez said.

No word on what the researchers will tackle next, but here’s hoping that the “beer before liquor, never been sicker” axiom gets some long-overdue attention.