Why Does Bonking Beer Bottles Create Foam? – Instant Egghead #66


[Scientific American] [Instant Egghead] [Clink] That is a terrible thing to do to a beer. All that delicious, malty goodness
gone to waste. But, why should a tap on top
trigger a foam explosion, while a clink on the side signals
the start of a drink with friends? It has to do with
the shape of a beer bottle. When you “bonk” a beer bottle on top, the hit creates pressure waves
that travel down through the liquid. These waves bounce off the bottom
of the bottle, head back up to the top, and then bounce back down again. The changing pressure in the beer rapidly
expands and contracts any small bubbles. At a certain point, these bubbles
burst under the pressure, creating thousands of tiny new bubbles. Here’s where the chain reaction starts. Each one of these tiny bubbles has
a lot of surface area for its volume, so it’s easy for the carbon dioxide
dissolved in the beer to get into the bubble. The bubbles get bigger,
getting lighter as they go, which makes them rise towards the top. As they rise, they pass through
new parts of the liquid, with lots of spare carbon dioxide. A feedback loop starts: the bigger the bubbles get,
the faster they rise, the more CO2 they absorb,
which makes them get even bigger. The process is not unlike
the mushroom cloud of the nuclear bomb- the violent result of
an uncontrolled chain reaction, and, depending on one’s mood,
only slightly less tragic. For Scientific American’s Instant Egghead,
I’m Michael Moyer. [Music] [English subtitles by
moomoo & NagySandor.EU]