The first rule of preserving your wine is to replace the cork correctly. While the “clean” side may seem easier to fit in the bottle, resist. The stained side has already been exposed to the wine, and it tasted fine. That “clean” side may not be so clean, and it can taint what you’re planning to drink in a day or two.
Air flattens your wine, lessening flavors and aromas. To minimize air exposure, use a funnel to pour the remaining vino into a screw-cap half bottle. Even if there’s a little air at the top, it’s far less than in a regular bottle.
It’s amazing how often people will keep leftover wine on the counter after they’ve recorked it. You wouldn’t do that with food, so don’t with wine. The cool temp can’t stop exposed wine from breaking down, but it can slow the process significantly.
If popping high-end bottles is what you call Wednesday (or you’re itching to taste those gems in your cellar), it may be time for a Coravin. This device, which looks much like a Rabbit opener, pierces the cork with a needle and tops the bottle with argon gas. Pour what you want, remove the needle and the cork will seal naturally. Many restaurants use it to sell top-shelf wines by the glass. There are other wine preservation options, as well.