Few things are worse for wine lovers than when a bottle of wine turns into vinegar. This happens when oxygen interacts with wine - the oxidation process begins the second a bottle of wine is opened. Generally, red wine will keep for about two to three days before the acids in the wine begin to develop. White wine stores for slightly longer in the refrigerator. In either case, wine should be properly sealed off from air soon after opening to preserve the fresh taste. Unfortunately, any opened and unused wine will start to turn to vinegar after about a week, no matter what you do.
Seal the wine off from the oxidation process. Use a wine vacuum kit to accomplish the sealing affect. Place the rubber vacuum stopper in the bottle. Place the hand-pump vacuum on top of the stopper and pump the air out. You will feel a resistance from the pump when the oxygen has been sufficiently sucked out. The rubber stopper is reusable as well.
Replace the oxygen in the bottle with prepared gasses that preserve the wine. These gasses consist of nitrogen, carbon dioxide, and argon and will replace the oxygen in the opened bottle. This mixture should be readily available at liquor stores. Spray the inside of the bottle with the mixture and seal off the bottle with the original cork.
Store the wine in the refrigerator. This will keep the wine fresh for slightly longer than leaving it out at room temperature. This can help keep the wine from turning into vinegar for about a day or so longer.