When you've drank half of a big plastic bottle of a fizzy drink, what is the best way to keep it fizzy? My wife crumples it up to squeeze air out, whilst I leave it full of air to keep mor pressure in - who is right?
Paul Climie, Glasgow Scotland
- I'm not a chemist or a physicist, but I'll have a go at this one anyways. Carbonated drinks do not 'fizz' when the air pressure above the surface of the liquid is high. Before you twist open the cap on the 2 litre bottle, it's not fizzy -- but when you twist the cap and a lot of air **comes out** (ie the air pressure in the bottle is decreased), the liquid is exposed to the lower ambient air pressure and so then begins to expel the potential gas which is impregnated in it. It goes bubbly. Following the same logic, if one were to want to stop this fizzing process, one would need to **increase** the air pressure in the liquid's container (ie pump a lot of air into it so that the gas is retained within the liquid -- there's no atmospheric 'room' for it to expel into). I can only that squeezing the excess air out of the bottle probably serves to lower that ambient air pressure even futher and causes the bubbles to be expelled at a more rapid rate. Many people seem to think they're 'preserving' the drink by trying to create a vacuum in the bottle, but I don't think it's of any use. In other words, I believe your wife is flattening your pop.
Lisa Sergent, London UK
- Fizz-keepers are still available - I have three bought very recently and they work well and do not leak if properly screwed in to start with. The problem with them is proper cleaning after use.
Susan Deal, Sheffield UK
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