Why does beer bubble up and “explode” when you tap the top of it?

Question

Why does beer bubble up and “explode” when you tap the top of it?

In: Chemistry

Answer 1

I’m assuming you’re referring to the effect when someone taps the top of a beer bottle with another beer bottle and the beer erupts and overflows. Basically, when you hit the top of the bottle, the bottle moves downward, but the beer inside it doesn’t. This creates an area in the bottle where there isn’t beer, and there isn’t air. It’s called a “cavitation” and when the cavitation collapses, it can release an intense shockwave. This shockwave will knock the dissolved carbon dioxide out of the beer which leads to the foaming.