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Soda Popinski
December 10, 2009 4:31 AM   Subscribe

When you pour soda into a glass, is the head / froth / bubbly stuff at the top actual soda that is being turned into froth and then wasted?

I have a debate with my girlfriend. I say that when she pours soda into a glass without tipping it, the head / froth / bubbly stuff that fills half the glass and then disappears downward is actual soda that is somehow combining with air and being wasted when it disappears.

She says that it's not soda, it's just something that comes out of the soda when you pour it that way.

Who's right?
posted by meadowlark lime to Science & Nature (12 answers total) 3 users marked this as a favorite
 
It's bubbles from the carbon-dioxide used to 'carbonate' the drink (nice how that works out, right?)

Yes, a tiny amount of liquid MAY atomize and disperse with the gas, but the amounts we're talking about are hard to measure without serious gear. Not enough that I would even consider it 'waste', especially since most will settle back into the glass.
posted by pupdog at 4:36 AM on December 10, 2009


The bubbles contain carbon dioxide gas that was dissolved in the soda under pressure, and the outside "skin" of the bubbles is made of (flat) soda. When the bubbles burst, the gas goes off into the air and the liquid remains in the glass. This is why a freshly-poured glass of soda is more effervescent than one that has sat around for a while. So it's not quite "soda" that's being wasted when the froth goes down, it's the gas in the soda. If you like to belch loudly, make sure you drink your soda immediately.
posted by letourneau at 4:39 AM on December 10, 2009


Pour a glass so that the head rises to just below the rim. Cover the rim with your hand until the head goes down. Is your hand wet? That wetness is the liquid that could have left the glass.

It looks like vigorously shaking and de-foaming a 450 milliliter bottle of Pepsi, fifteen times, removes a couple of grams of carbon dioxide. That's about 0.5% of the mass of the liquid in the bottle. If your vigorous pour were like the first bottle-shake in that experiment, then the "head" is associated with about 0.3 grams of carbon dioxide leaving the solution; 90% of the carbon dioxide stays in solution. That 0.3 grams of carbon dioxide has a volume of 150 milliliters, which is one-third of the volume of the bottle.

So if you pour a glass of soda three-quarters full and the head immediately rises to the top of the glass, then about 90% of the carbon dioxide is still dissolved in the liquid.
posted by fantabulous timewaster at 5:12 AM on December 10, 2009


Don't just take our words for it. Do an experiment. Take two identical carbonated drinks, and two identical glasses. Pour one drink into a glass carefully, pouring it down the side with the glass starting at an angle to minimise the foaming. Pour the other one into the other glass rapidly and straight into the middle to maximise foaming. (In each case let it settle occasionally to prevent it foaming over the edge of the glass). Once you've emptied the cans into the glasses, compare the levels of the two. This will show you how much (or little) has been lost.
posted by Electric Dragon at 5:22 AM on December 10, 2009 [6 favorites]


Concurring with the opinions above. You lose more liquid from the slight fizz of popping bubbles--pour a glass of soda quickly then hold your hand over it; it'll get wet--than you do from the foam itself. It's just dissolved gas escaping.
posted by valkyryn at 5:34 AM on December 10, 2009


I agree with Electric Dragon. Science fun is much better than arguing with a loved one over something trivial.
posted by GenjiandProust at 5:50 AM on December 10, 2009


Since carbon dioxide is just a colourless gas, the manifestation of the bubbles represents the liquid material of the drink forming a thin film being stretched into the bubble shape as the gas moves out of solution and escapes into the air. The actual surface of the bubble or bubbles is soda (though it will still have some dissolved CO2 still in it), while the CO2 is keeping them in the bibble shape. As the film bubble fails the CO2 escapes and the film soda falls back into the glass.
posted by biffa at 6:03 AM on December 10, 2009


Pour a glass so that the head rises to just below the rim. Cover the rim with your hand until the head goes down. Is your hand wet?

Just because your hand is wet doesn't mean that the wetness on your hand is soda that would have been lost. If your hand wasn't there, most of that liquid would fall back into the glass.
posted by missmagenta at 6:21 AM on December 10, 2009 [2 favorites]


It's not the liquid you're worried about losing; it's the carbonation.

If you like your drink really fizzy, tip the glass. If you think soda is too fizzy, then pour it with a head, this allows some carbonation to escape.
posted by surenoproblem at 7:39 AM on December 10, 2009


Seems I was definitely in the wrong here! I'll direct my better half to this thread.
posted by meadowlark lime at 8:14 AM on December 10, 2009


If you run the experiment, pay attention to the line dividing liquid soda and froth. I'll bet you see it rising slightly as some of the soda that was in the froth rejoins the liquid soda.
posted by soelo at 1:47 PM on December 10, 2009


The "froth" is the liquid of the soda and carbon dioxide. If you consider the carbon dioxide gas bubbles as part of the soda, then you're losing a small portion of the complete package. If she's implying that the liquid in the foam is different from what is in the rest of the glass, then she's wrong. It's just a frothy mixture of liquid, CO2, and other air that's mixed in during the pouring process.
posted by mikeh at 8:13 AM on December 11, 2009


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