Wine is made through the fermentation of grape juice. When yeast and sugar are added to crushed grapes, a chemical reaction takes place in which the sugars in the grapes are added to the mixture are converted into alcohol. During this fermentation process, certain acids and bacteria work to change the taste of the grape juice into a more rich, slightly bitter and complex liquid, resulting in wine. While the alcohol helps to preserve the wine and extend its shelf life, sometimes the acids and bacteria that help with the fermentation process can eventually end up spoiling the wine, destroying its flavor and rendering it undrinkable.

Not all wines are created equal, and while some of them can last for up to 100 years if unopened, others may only last for a few years. Generally, red wine lasts longer than white wine because of the tannins contained in the skins of the crushed grapes and the wood of the wine barrels used to make it. Tannins act as a natural preservative. Grape skins aren't used to make white wine so it contains less tannins and lasts anywhere between one and two years. Red wines can last from two to three years. Fine wines and dessert wines can last much longer, usually for over 10 years.

To maximize your wine's shelf life, store bottled wine on its side to keep the bottle's cork moist and air-tight. The ideal temperature for wine storage is 55 degrees Fahrenheit, but you can generally store your wine between 45 and 65 F, recommends Wine Spectator Magazine Online. Keep the humidity level in the dark room in which you store your wine at around 70 percent. A wine cellar, spare closet or specialty wine cooler make ideal spots to store your wine. Once opened, though, you'll need to refrigerate your wine and drink it within three days to two weeks.

The reason that wine eventually spoils is that oxygen allows certain bacteria in it to flourish and form unpleasantly-flavored acetic acid within the liquid, essentially turning it into a form of vinegar. These acids and bacteria give the wine a sour, sharp and unpleasant taste. Vinegar can last indefinitely, which is why some believe that wine can't spoil because it transforms into vinegar, although it isn't vinegar that tastes very good. Sometimes, if the wine maker hasn't properly sterilized his equipment during the production of his wine, harmful bacteria can contaminate the wine, even when it's stored properly. If your wine smells and tastes moldy, stale or overly acidic, it's time to discard it.