The idea of letting the wine breathe comes from the fact that before a newly bottled wine is corked and sealed, the air has to escape. When the air is removed from the bottle, no contaminants can enter it (in much the same way that air is removed from the jars of home grown vegetables that we can,) and no air can get into the bottle.
What is aeration?
Aeration is the term that wine experts use to indicate the practice of allowing the wine to breathe. All wines are supposed to be allowed to breathe before they are consumed. When the air is allowed to interact with the wine, then the aromas are released from the bottle. Part of the wine tasting experience involves being able to smell the aroma.
Aerating in the bottle –
White wines are generally allowed to breathe in the bottle. Once the wine is uncorked, it can be allowed to sit out before it is consumed. Many people think that roughly 30 minutes is a good amount of time to allow the wine to sit. Since white wines are served cold, one can always put the bottle in a bucket full of ice, just as one would do with a bottle champagne.
Decanting wine for aeration –
Red wines can be allowed to breathe in more ways than in the bottle. One way is to decant the wine. When the wine is poured into a decanter, the theory is that the body of the decanter is wider than the body of the wine bottle and therefore, there is more room for air to enter the decanter. Because the decanter isn’t sealed with a cork or cork like device from which air can be removed, the wine is essentially exposed to some air at all times.
Aerating in the glass –
Sometimes when many people are drinking wine, the easiest way to ensure that everyone’s wine gets aerated is to pour it into the glass. The reason the mouths of wine glasses are as wide as they are is to allow the wine to breathe, and to make it easier for the wine drinker to take in the aroma of the wine as they drink it.
Allowing wine to aerate or breathe in the glass is more acceptable for red wines than it is for white wine, especially if the desire in serving white wine is to ensure that it is cold when everyone is ready to drink it.
Using a carafe –
With especially large bottles of wine, the easiest way to allow the wines to breathe properly is to pour them into wine carafes. A carafe of wine can be large enough to serve three or four people, or carafes can be small enough to serve one or two people. At restaurants, banquets and other places where many people are dining together, sometimes it seems more polite or aesthetically appropriate to pour wine into a carafe rather than to allow the bottle to be seen.
Because red wines are much more aromatic than white wines, the desire (or perhaps need,) to allow the wine to breathe is stronger with red wines. As the wine breathes and imparts its aroma into the air, the flavor will be fully discernible, and for wine tasters, connoisseurs and those who drink wine for the health benefits, the flavor is every bit as important as the aroma.