There are many stuffy rules about wine, from the type of container it should come in to how expensive it should be. One common myth is that a bottle of wine should be fully consumed the same day it's opened. While it's true that vino does start to oxidize the moment the cork comes out, that's no reason to guzzle a liter of it all by yourself, or pour your leftover liquid down the drain. According to Bon Appétit, an open bottle of wine is still good for several days—as long as you know how to store it properly.
If you pop open a new bottle of cabernet just to have a glass or two, hold onto the cork. Corks have been an important part of the wine-making process for centuries. The material is dense enough to keep liquids fresh without sealing off air altogether. A minimal amount of oxygen allows the flavors of the wine to continue to develop, while too much oxygen creates an acrid, unpleasant taste.
Once you've finished pouring your wine, squeeze the cork back into the bottle to prevent any more oxygen from reaching the drink. If you've damaged or accidentally tossed out your cork, a bit of plastic wrap with a rubber band, aluminum foil, or a reusable wine bottle stopper will work, too.
Storing your opened wine in the fridge limits its exposure to other damaging elements like heat and light. Once it's refrigerated, most red and white wines will last two to five days before their flavors take a turn for the worse. Sparkling wines, however, have about one to three days before they're no longer drinkable, and some natural wines can go bad in a day. The highly tannic red wines available at the supermarket generally last the longest after being opened, with a lifespan of up to seven days.
Because expiration dates vary so greatly between wine varieties, the best way to judge the freshness of what's in your bottle is to give it a taste. Overly oxidized wine doesn't taste great, but drinking a test sip of it won't make you sick. If you'd rather avoid drinking potentially spoiled wine, you can also judge its quality by sight and smell. Wine that's developed a brown tint and/or a vinegary smell has oxidized, meaning it's time to toss it and open a fresh bottle.