The In-Depth Science of Why a Beer Bottle Erupts When You Whack It

“Beer tapping” is the kind of jerky thing that jerks do at bars. They walk up to you—you with your nice, cold bottle of beer, the one you’ve been looking forward to all day while you were working at your hard, stressful job—and they thump their bottle down on yours. Your beer erupts in a foamy mess. You can try to catch some of that quickly disappearing beer, if you want. But, really, it’s gone.

But then, when you’re done being annoyed, you think: Why did my beer do that?

The answer, it turns out, is super complicated, and has to do with the physics of small bubbles and the power of a reflecting pressure front.

Why does a beer bottle foam up after a sudden impact on its mouth?

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According to Physics Central, it is possible to stem the eruption.

ou can keep the bubbles from growing and creating plumes by quickly plugging the bottle with your thumb until the carbon dioxide has a chance to dissolve back into the liquid – much like re-capping a soda bottle if it starts to spew everywhere upon opening.

But, they say, it wouldn’t be easy: “From the time of the tap to the first implosion of a single bubble, about one millisecond passes – too short for human reaction to kick in.”

More from Smithsonian.com:

Beer Behemoths, Part One
Science in the Public Interest: The Beer Koozie Test
From Elephant Poop Coffee Comes Elephant Poop Coffee Beer

Colin Schultz | | READ MORE

Colin Schultz is a freelance science writer and editor based in Toronto, Canada. He blogs for Smart News and contributes to the American Geophysical Union. He has a B.Sc. in physical science and philosophy, and a M.A. in journalism.