The Fascinating Science Behind Beer Foam

RenderSeven writes "Science has so far been at a loss to explain why tapping a beer bottle with another causes it to explosively foam over. Thanks to a grant from the Spanish Ministry of Economy and Competitiveness, a research team at the University of Madrid studying fluid mechanics has found the answer with some fascinating slow-motion video. Their soon-to-be-published paper found that tapping the bottle (or shooting it with a laser) causes a series of compression and expansion waves, that generate unstable buoyant plumes, quickly turning most of the liquid into foam. PhysicsBuzz notes that the process is very rapid and nearly unstoppable once started."

I make beer...

[dargaud]

...and foam is a mix of two things: a gas (here CO2) and a liquid that can hold the gas, meaning something a lot more complex than water. Usually it's a mix of proteins, in a way similar to the way gluten holds the bubbles inside the bread to let it rise. I have some bottles that, if opened brutally, will turn entirely to foam. Others will have the wanted 'normal' foam: a few inches which lasts for a long time. Others have lots of gas but no foam. Soda makers in recent years have actually started adding anti foaming additives to their drinks; have you noticed that you can't shake a friend's coke and have it explode in his face anymore ?

Re:I make beer...

[gstoddart]

Ah... that explains it. I had become somewhat nervous about the beverages handed to me by my grade school son ever since he learned about that prank. Nothing ever happened

I learned a long time ago how to open a can without too much fear of this.

Tap the top of the can a couple of times, and crack it open just enough to let a small amount of pressure escape, and wait a little while. It might foam a little, but you can actually 'burp' off most of the pressure if you're careful.

Even back in the 80s I could open a can which had been shaken without much incidence of spraying. And I've always opened cans that way since because, well, my friends weren't good, thoughtful kids when it came to that. ;-)

Re:I make beer...

[OglinTatas]

You'll see that on plastic soda bottles (pop bottles, depending on your origin) the threads are broken by gaps. This is to allow you to do just that-- crack the top and let the pressure release. You may have to crack/seal it a few times to safely remove the top.
If the gaps were not there, you would have to unscrew the top much further to vent, and you would risk blowing the cap off and an ensuing fountain of foam.