Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Steven Wasmer on 02/11/2011 15:30:03

Title: Why does beer foam overflow from the bottle?
Post by: Steven Wasmer on 02/11/2011 15:30:03

Steven Wasmer  asked the Naked Scientists:
   
Hello Scientists!

Excellent programme. (http://www.thenakedscientists.com/HTML/podcasts/)

I was wondering why when you strike a full beer bottle on the top with the base of another beer bottle the beer will very quickly expand and squirt out the top?  I've done some research and found references to vibrations of the bottle, and cavitation.  Is this correct?  Does the shape of the bottle have anything to do with it.  Obviously the narrow neck increases the foams velocity but as far as I know you can't get any foam at all when doing the same thing with cans.   On a related note I was wondering if, since CO2 bubbles need a point for nucleation, can C02 themselves serve as a nucleation point?  If so why doesn't the C02 come out of solution exponentially?

Keep up the good work. (http://www.thenakedscientists.com/HTML/podcasts/)

Steve Philadelphia  PA

What do you think?

Title: Why does beer foam overflow from the bottle?
Post by: Soul Surfer on 03/11/2011 20:57:42

Striking the bottle with a hard object in particular on the base of the full bottle creates rapid ultrasonic vibrations which cavitate (that is the negative pressure at the negative peak of the sound waves is great enough to open a cavity in the liquid filled with water vapour in the liquid at the bottom of the bottle).  All fizzy drinks are supersaturated with carbon dioxide and this rapidly comes out of solution to fill the cavities and expand the bubbles and these then rise rapidly to the surface to create the fountain.  It is as you suggest a nucleation process  you can have a similar effect by adding a range of finely divided or soluble substances to the beer.

Title: Why does beer foam overflow from the bottle?
Post by: JP on 04/11/2011 01:19:56

Good explaination, SS.  I always thought it was because it was trying to get out of the bottle and into my belly as fast as possible!

Title: Why does beer foam overflow from the bottle?
Post by: Geezer on 04/11/2011 06:14:36

Ah, right! Good one SS. What happens when you merely shake a can of your favorite carbonated beverage (adult or otherwise). That seems to "arm" the CO2 in some way so that a lot of the contents are ejected when the seal is broken. 

Title: Why does beer foam overflow from the bottle?
Post by: Bored chemist on 04/11/2011 07:28:44

" but as far as I know you can't get any foam at all when doing the same thing with cans.  "
Yes you can.