How long does a bottle of wine last after it is opened?
The short answer is: as long as it still tastes good to you. Wine doesn’t really ever go bad, it just starts to taste nasty to most of us after a while, and eventually becomes vinegar.
But that's not very helpful. Let's dive in.
Before it has been opened, wine exists in its bottle with almost no air contact. The bottling process usually involves displacing all the remaining air after filling a wine bottle with an inert gas such as nitrogen or argon before the cork goes in.
We care about how much air gets in because wine, when exposed to air, starts to oxidize and begins its journey towards salad dressing.
There are two things you can do to make your wine last longer once you’ve started to drink it. One is to keep it exposed to as little oxygen as possible (bacteria need air in order to metabolize the alcohol), and the other is to slow down the metabolism of the bacteria (so the conversion to vinegar takes longer) by keeping temperatures low.
In short: put the cork back in the bottle, and put it in the fridge. Most white wines will last up to a week or more in the fridge. Red wines with higher acidity will last 4 to 7 days before they start to taste funky to me, and sparkling wines closed with a proper sparkling wine stopper will last a week or more depending on how much wine is left in the bottle.