So what happens if you do not finish a bottle of wine? How long is that bottle of wine good for after it has been opened? The answer is, not very long, unfortunately. Once you start getting oxygen into the bottle your wine is making the slow and steady march towards becoming vinegar.
What you want to do is slow down that progress. There are a few different tools out there that you can use to sort of stop the oxidation. For example, you can inject them with a little bit of argon gas which can work for a little while. My best recommendation is to put a cork in the bottle and put it in the refrigerator. Even if it is a red wine. That will actually slow down that aging process. It will still only last for a few days, but it will certainly last longer than if you leave it on the counter.
Learn Wine featuring Master Sommelier Emily Wines