The process of “breathing” in wine terms, is a process whereby we allow the wine to be exposed to air. We do this to allow the process of Oxidation.
Although oxidation normally has a negative effect in wine on a long term basis, exposing some wines to oxidation has its benefits in the short term. This oxidation changes the wine as it can help soften flavours 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.
The best way to Air a wine is to use a decanter - A 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. Just opening a bottle of wine and leave it there might not be enough to effectively air the wine as the amount of wine exposed to oxygen is minimal.