Science Of Beer Tapping: Why A Bottle Foams Over When You Hit Its Top [VIDEO]
If you've ever had a beer, you've probably at some point taken a beer bottle and lightly tapped it on top of a friend's bottle, bringing about a rapid, sudsy explosion and perhaps several curse words. Scientists in France and Spain have now figured out why this happens (why the beer foams like that, not why you would do such a thing). It turns out that beer tapping leads to a foamy overflow because of something called cavitation.
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Cavitation is the formation of vapor cavities--more commonly known as bubbles--in liquid. With beer, when you tap one beer bottle to another, it sets off compression and expansion waves. These waves break up the beer's "mother" carbon dioxide bubbles, which give birth to clouds of tiny "daughter" bubbles. The daughter bubbles grow in size very quickly, causing foam to form and spill out of the bottle like a baking soda volcano. The whole process takes only a second or so, but the laughs last long beyond that.
"Buoyancy leads to the formation of plumes full of bubbles, whose shape resembles very much the mushrooms seen after powerful explosions," said lead researcher Javier Rodriguez-Rodriguez of Madrid's Carlos III University. "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."
The beer tapping research isn't as frivolous as it might seem. Cavitation is a cause of the erosion of ship propellers, to give an example, and the researchers cited the Lake Nyos disaster as a case in which cavitation research could be helpful. In 1986, Lake Nyos suddenly released between 100,000 to 300,000 tons of carbon dioxide, creating a gas cloud that suffocated about 1,700 people and killed 3,500 livestock.
The beer tapping research was presented yesterday at a meeting of the American Physical Society Division of Fluid Dynamics. Those guys throw some wild parties, so it's probably safe to assume a whole lot of beer tapping was going on. Especially if any of those folks are from North Dakota or New Hampshire.
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