soda fizz

[sisuboy]

Bet-settling time --

What is the best way to maintain the fizz/carbonation of a 20-oz. screw-top soda bottle that is to be drunk over 20 minutes or so: (1) replace the cap tightly after each drink, (2) replace the cap loosely after each drink (allowing some air to enter/exit the bottle), or (3) leave the cap off altogether?

Any thoughts appreciated.

[Chronos]

Replace it tightly each time. You want the internal pressure to stay as high as possible, and because of CO2 coming out of solution, it will naturally tend to be at a higher pressure than the outside. If the cap is loose enough to allow gas exchange, or off entirely, the internal pressure will stay the same as ambient air pressure.

[Demo]

Crap, this reminds me of this moron in high school...well, actually a whole family of morons. Somehow, they had come to the agreement that squishing a 2 litre bottle so all the air was out would keep the carbonation in the soda longer. I kept telling them that they were just creating an environment where the CO2 could leech out even easier than leaving the lid off. Did they listen to me? Nooooo! Dumb bastards!

Oh well, to address the OP, what Chronos said.