That is, keeping the CO2 in solution in a sealed half empty bottle of (say) Cola. I have seen two methods claimed keep the drink fizzy. The first is one which I think is worse than nothing, which is to squeeze the air out of the bottle before screwing the top on. I would think that this just induces a negative pressure which helps remove the gas from solution. The other method is to use a little pump in place of the cap to increase the pressure in the bottle by pumping in air. Not sure what effect that might have, but it does seem plausible.
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1Snarky answer: don't open it in the first place? – Kyle Kanos Mar 29 '16 at 10:25
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2This might also be a good question for lifehacks.stackexchange. – Martin Mar 29 '16 at 14:20
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The amount of gas that can be dissolved in water before it wants to come out (thermodynamic equilibrium between dissolved gas and atmospheric gas) is proportional to the pressure. Makes sense, putting more gas above the liquid will force more molecules into the water (this is put very crudely - to do it properly, you have to look at the chemical potential balance).
So, increasing the pressure will keep the gas in. That's what holds it in before you open the bottle, and when you hear the pffft, the pressure in the bottle drops and the dissolved gas starts esacaping.
Solubility drops if you increase the temperature, so keeping the drink cool will preserve the fizz. Roughly speaking, the concentration of dissolved gas goes like this $$c\propto p/T $$ where the proportionality constant depends on the gas. Read up on Henry's law to know more.
orion
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