If you're drinking a good bottle of wine, there shouldn't be any left over, but if you're drinking a lot or hosting a party, you may need a way to keep half-poured bottle fresh overnight or for a few days. You could re-cork it, but air is an open wine's worst enemy. Wired tested some alternatives that make the grade.
It's remarkable how much of a cottage industry there is around wine preservers that will either pump the air out of a bottle of wine, leaving a vacuum in its place or inject a kind of inert gas into the bottle to replace the air. Granted, air has its purpose, but too much or prolonged exposure will spoil a wine pretty quickly. Wired explains:
Let me step back a second. Air serves a very important purpose when you're drinking wine. Most importantly, it "opens up" a wine and helps to bring out its character. When you slosh wine from a bottle into a glass, a lot of air gets mixed in. This causes those aromatic compounds to fill the glass and makes the experience of drinking a good wine all that much better. There are decanters and aerating gadgets to speed up this process, too, if swirling's not your thing.
But once air gets to the wine, the cat is out of the bag. While it will taste fantastic for a few hours, it will then slowly lose its fruitiness, its aroma, its body, and just about everything else. Eventually the wine will oxidize due to exposure to O2 in the air, which starts a chain reaction in the wine, forming hydrogen peroxide, then acetaldehyde, neither of which you want to be drinking a lot of. Once a wine is uncorked (or once the cork starts to fail), this process begins in earnest.
So to combat that longer-term exposure, the kind that doesn't happen in your glass, they tested an array of wine preservation gadgets, from simple hand-operated pumps that seal the bottle and pump out the air to needle-injected gas canisters that you mount on the bottle before you even uncork it. They run the gamut from cheap (~$10) to super-expensive (~$350), and everywhere in between.
Bottom line, Wired discovered the most effective methods were the ones that replace the air in the bottle with some kind of inert gas that won't oxidize your wine. The most effective tool they tested was a simple $9 canister of inert gases that looks like a can of compressed air. It's tricky to use (you essentially spray the gas into the bottle and then put a stopper in it as fast as you can) but it was even more effective than the fancy $350 argon injector.
Check out the full reviews at the link below—it's good to know that if you ever do have leftover wine, you don't need to spend a fortune on gimmicks to keep it tasting fresh the next day.