by James Hunt
From Coca-Cola to carbonated water, there isn't a fizzy drink around that tastes better once it has gone flat. As soon as you break the seal on the bottle, it's a race against time to finish off your soft drink before the precious bubbles that make the drink taste better are depleted. The last thing you want to do is speed up that process.
That's why we had to know: Does laying a bottle on its side make a soft drink go flat more quickly? Or is it nothing more than a consequence-free way to cram more and more of them in the fridge?
To figure out the answer, you first have to understand why fizzy drinks go flat at all. The carbonation in soft drinks is a result of additional carbon dioxide being dissolved into the liquid, which is then sealed under pressure. When the container is opened, the difference in pressure allows the carbon dioxide to form into bubbles, which then rush to the surface and escape back into the air. As each bubble bursts, the drink becomes a little less fizzy.
This process can theoretically continue until the drink contains the same amount of carbon dioxide as the atmosphere around it—though the drink will seem flat long before that point.
So does it matter if the container is on its side?
The answer: Not really. While it's true that a bottle that is lying down will have a greater area of contact between the liquid and the air inside the bottle, that's a small enough factor that any effect on the speed of carbon dioxide dissolution will be negligible. Since carbon dioxide bubbles form, or "nucleate," on the side of the bottle, increasing the surface area between the drink and the air might actually make it go flat slightly slower if the bottle is on its side—but again, this effect isn't pronounced enough to make much of a difference over anything other than very short time scales.
What really matters when it comes to keeping a drink fizzy is the pressure inside a sealed container. As the carbon dioxide escapes, it builds up the pressure in the air within the bottle, until it's high enough to prevent bubbles forming, which keeps the liquid fizzy. The pressure inside an opened bottle of soda that has been resealed is virtually the same, whether or not it's standing up or on its side.
Things that do help keep drinks fizzy include chilling (carbon dioxide dissolves into air more readily at higher temperatures) and screwing the cap on tightly to help keep the pressure within the bottle high.
Squeezing the bottle doesn't help, unless you keep it squeezed until the next time it's opened—otherwise, the carbon dioxide will just escape the liquid and deform the bottle back to its original shape. Indeed, the fact that there's no air inside the bottle will effectively suck extra carbon dioxide out of the drink in an attempt to equalize pressure inside the container, so squeezing the bottle actually makes the drink go flat more quickly than the alternative.
And finally, those repressurizing pumps? They'll only work if you pump in something that contains more carbon dioxide than the drink. Air doesn't, so the extra air you pump in creates a high-pressure mix of mostly oxygen and nitrogen, which—if anything—helps forcibly displace the carbon dioxide in the drink by encouraging oxygen and nitrogen to dissolve.
Whew. Knowing all that, the main tip for keeping your drink from going flat before you finish it? Keep it cold until you're ready to drink it, then chug it down. Your dentists and doctors might not thank us, but your taste buds will.
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