Why does beer foam over the top of the bottle, when hit on the top by another bottle?

Question

What causes beer to foam up when you hit the top of that bottle with the bottom of another?

Answer 1

The beer has carbon dioxide dissolved in it and is in equilibrium. Some of the carbon dioxide are gaseous and other part is dissolved in the beer. You can see it in a glass of beer where bubbles clinging to the sides.

When you bonk the beer, you impart a little energy into the beer. The bubbles are knocked off the bottle/glass into the rest of the beer, the equlibrium is shifted towards the gassy side which causes more carbon dioxide to come out of solution, thus foaming over.

Answer 2

The abrupt impact creates pressure on the liquid. That pressure turns into gas. The gas bubbles up and creates foam. Because of the small hole, the pressure and foam (for lack of a better word) bottlenecks and erupts like a volcano.

Happy chugging.

Answer 3

The hopps gives it the head(foam)

Answer 4

hmmm dunno