Beer Tapping Physics Explained
November 25, 2013

Science Of Blasting Beer Finally Explained

Alan McStravick for - Your Universe Online

My first experience with the behavior of forcefully tapping the bottom of a beer bottle to the top of another, creating a foamy overflow, was in the rowdy crew bar of the Queen Elizabeth 2 on which I served in the entertainment department in my much younger days. And more than one bottled brew was significantly emptied onto the bare floors of one frat house party or another during numerous college weekends. Now, thanks to a group of researchers in Europe, we have a clearer scientific understanding of how this hilarious phenomenon occurs.

Cavitation, an engineering term most commonly associated with maritime issues like the erosion of ship or submarine propellers, is also a concept pertinent in the production of bubbles in a bottle of beer after a sudden impact. This was driven home in a presentation by researchers from Carlos III University in Spain and Universite Pierre et Marie Curie, Institut Jean le Rond d’Alembert in France, made Sunday at the annual meeting of the American Physical Society Division of Fluid Dynamics.

The team, led by Javier Rodriguez-Rodriguez, explained how a sudden and forceful impact against the mouth of a bottle will cause the bottle to have a back and forth movement of both compression and expansion waves that will, in turn, cause bubbles to appear before quickly collapsing. The cavitation-induced break-up of the larger ‘mother’ bubbles, says the team, creates overwhelming clouds of much smaller carbonic gas ‘daughter bubbles’. It is the smaller bubbles, which are able to grow and expand at a much faster rate than the larger bubbles from which they split, that are responsible for the volcano-like over-topping of the struck bottle.

Speaking with former redOrbit writer and now-Head Brewer for Wahoo Brewing Company, Michael Harper, his take on the phenomenon explored both the practical and the punitive.

“Outside of the classic frat house prank,” says Harper, “brewers have known about cavitation for years and have even used it to their advantage.” He then detailed a particular instance when, on a malfunctioning bottling line, a master brewer advised his staff to use a screwdriver to tap the tops of the bottles, using cavitation to drive out “beer-ruining oxygen.”

With the daughter bubbles achieving buoyancy in the liquid-filled bottle, “[this] leads to the formation of plumes full of bubbles, whose shape resembles very much the mushrooms seen after powerful explosions,” explained Rodriguez-Rodriguez. “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.”  This, he claims, is because faster moving bubbles entrain more carbonic gas.

While many of us have either experienced this phenomenon firsthand or shared this experience with an unsuspecting friend, this current study 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-Rodriguez concluded.

The team’s presentation, entitled “Why does a beer bottle foam up after a sudden impact on its mouth?” was presented on Sunday and provides findings which will have wider application beyond the bar room. Certain to benefit will be other engineering systems. It will also increase our understanding of serious natural phenomena such as the sudden release of dissolved carbon dioxide in the Lake Nyos disaster.

In what could only be deemed an expression of the passion he feels for the world of lagers and ales, Harper concluded with a warning to any who might mistreat a malty beverage. “It is my opinion that anyone who wastes a beer should be hanged by their toes.”

Image 2 (below): A chain of physical phenomena occurring after your bottle is hit leads to a well-known consequence: your beer quickly turns into foam. Credit: Javier Rodriguez-Rodriguez / Carlos III University of Madrid, SPAIN Almudena Casado-Chacon / Carlos III University of Madrid, SPAIN Daniel Fuster / CNRS (UMR 7190), Université Pierre et Marie Curie, Institut Jean le Rond d'Alembert, FRANCE