Why does the foam on a glass of beer last so much longer than the foam on a glass of soda?!
Answers: And the reason I propose is that since beer is brewed from barley, there is a protein structure which exists in the beer. This gives support to holding the foam, properly called a head.
???
Natural vs compresed gas???
I am not sure, but I would venture to guess it is what the beverage is made of. Beer is the fermentation of grains and malts, which is thick, and soda is just flavored sugar water. Mmmmm....beer...... :)
its not always called foam, on stout;its a head.... and there is 4 reasons
1) beer is naturally more carbonated and thus would keep its head anyway(some stouts have a head that is completely separate from the stout itself and is ''off the top'' ie pulled differently and just sits on top for a different taste eg. an old man i serve gets a Guinness with a smitwicks head)
2) pint glasses are designed to keep a head longer hence the curve in the pint glass, or bumps in some...this is really just to make it look better...
3)pints are pulled from kegs through specialized taps(stouts can have 2 taps one for the stout and one ''off the top'')
4)in cans there's a widget; a specialized little ball that keeps the head in a flat can, if you shake anything that has a good head eg a stout or smithwics you'll hear a rattling even if its empty
but not all beers have a head some just have foam, as you said, and this is caused by carbonation, like in soda, but beer is just more carbonized, and has less water due to alcohol so stays as such for longer...
Nothing to propose, Joe is right. It's the protein in the beer that causes the thick head. Soda is actually more carbonated than beer. (A dirty or soapy glass will kill the head.)