Soda Fizz & Beer Foam

[jester21]

Probably a simple Question, but one that eludes me....

Why does soda fizz and Beer foam both disapate faster when you touch it, as opposed to just letting it disapate on it's own?


also, is beer foam created from the same carbonation as soda? Or is it something special in the beer brewing process?

That reminds me... I need beer. brb.

[Electronerd]

You can think of the foam as a bunch of tiny bubbles packed closely together. When you disrupt the bubbles, the carbonation is released and the small amount of liquid either remains on your finger, falls back into the beverage, or probably a mixture of both.

[antechinus]

The gas in the bubbles of beer and lollie-water is both carbon dioxide.

This gas is artificially dissolved in the lollie-water, whereas it is a product of fermentation in beer.

Bear foam is held together by waxes and proteins, which give the bubbles strength, thus slowing down their collapse. Lollie-water bubles colapse as soon as they hit the surface since there is no surface active agent to slow down bubble collapse.

Poking bubles with your finger disrupts the thin film of the bubble wall, thus promoting bubble collapse.

[TheLoadedDog]

Originally Posted by antechinus

This gas is artificially dissolved in the lollie-water, whereas it is a product of fermentation in beer.

Minor nitpick: most commercial beer has its gas artificially injected into it before bottling or kegging, just the same as for soft drink (but at a lower pressure). This is due to cost, the fact that most consumers don't like the sediment that comes with naturally conditioned beers, and also the pasteurisation process killing the yeast. For traditionally brewed beers though, you are quite right. Home brews and some boutique beers are naturally conditioned with extra fermentable sugars (and sometimes extra yeast) added at bottling, to provide natural carbonation.

[Kegg]

If your finger was wet, would it change things?
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[Squink]

Beer foam is more resilient than than pop fizz because beer has more proteins in it.

[flurb]

The oils from your skin do a wonderful job of breaking down the cohesion of beer foam. For a truly disgusting experiment, try running a finger along your nose, forehead or other oily area and then lightly touching a head of beer.

[Sigene]

Originally Posted by flurb

The oils from your skin do a wonderful job of breaking down the cohesion of beer foam. For a truly disgusting experiment, try running a finger along your nose, forehead or other oily area and then lightly touching a head of beer.

I've heard this explanation many times, but have not really been able to replicate the results. Sometimes my hands and fingers are clean and it happens; sometime I ensure I have body oils on my finger..and it doesn't happen. This is a science fair project dying to be performed. Right now I'm leaning to the oily finger hypothesis as being mythical.

[flurb]

Originally Posted by Sigene

I've heard this explanation many times, but have not really been able to replicate the results. Sometimes my hands and fingers are clean and it happens; sometime I ensure I have body oils on my finger..and it doesn't happen. This is a science fair project dying to be performed. Right now I'm leaning to the oily finger hypothesis as being mythical.

I'm afraid I can only cite anecdotal evidence. But logically, I'd think that the introduction of any fats or oils into the foam would disrupt the surface tension of the bubbles.

[antechinus]

Originally Posted by TheLoadedDog

Minor nitpick: most commercial beer has its gas artificially injected into it before bottling or kegging, just the same as for soft drink (but at a lower pressure). This is due to cost, the fact that most consumers don't like the sediment that comes with naturally conditioned beers, and also the pasteurisation process killing the yeast. For traditionally brewed beers though, you are quite right. Home brews and some boutique beers are naturally conditioned with extra fermentable sugars (and sometimes extra yeast) added at bottling, to provide natural carbonation.

True, but minor nitpick: these commmercial beers are not actually beer, as defined by the oldest food law, the Bavarian Beer Purity law of 1514.

Speaking of beer additives, cobalt has been added to beer to improve foaming. Not sure if it is still used anywhere.