Allowing red wines to breathe for a short time allows the wine to oxidize, soften the flavors and release aromas. doing this is a proper wine glass is best.
Allowing wine to breathe has the following information on this subject:
Allowing a wine to “breathe” is simply a process of exposing it to air for a period of time before serving. Exposing wine to air for a short time, or allowing it to oxidize, can help soften flavors and release aromas in a way similar to swirling the wine in your glass. Young red wines, especially those that are high in tannin, such as Cabernet Sauvignon, most Red Zinfandel, Bordeaux and many wines from the Rhône Valley, actually taste better with aeration because their tannins soften and the wine becomes less harsh. Another method of aerating a young, tannic red wine is to roughly decant it into another container, which exposes more of the wine's surface to air than simply removing the cork from the bottle. Uncorking a bottle and letting it sit undisturbed for period of time actually does very little to let the wine breathe as only a small percentage of the wine is in contact with air. A much better suggestion is aerating the wine in your glass or in a wine decanter. A decanter is defined as any vessel other than the original bottle that will hold the contents of the wine and allow for air to mix with the wine within. Usually, these are broad-bottomed glass or crystal containers.
Wine and air may have a negative effect on each other. To simplify, let us consider the following:
• Wine poured from a bottle into a glass and swirled is positive since the air mixture allows aromas to be displayed
• Wine that has had a brief exposure to air is positive since it allows wine to breathe similar to stretching its legs after being cooped up in the bottle for so many years. This exposure has a positive effect on the wine after 25 to 30 minutes. Intensely tannic or younger reds may need up to a few hours. In general, most red and white wines will improve within the first half hour of opening the bottle.
• Extended exposure to air has a negative effect on the wine. After a day, the wine may obtain a vinegary smell or taste. Red wines and sweet white wines may last a little longer due to the natural preservatives of tannins and sugar. Refrigeration may be used to extend the life of white wine.