Definition - What does Aeration mean?
Aeration, also known as breathing, is the process of introducing oxygen to wine. This helps the scent of a wine become more noticeable. It also helps to round and soften the wine while opening up the wine to release its aromas. Since simply pulling off the cork is not enough for oxygen to be absorbed, decanting and swirling are some methods used to allow sufficient air contact.
WineFrog explains Aeration
The exposure to air can be beneficial to young red wines, as it helps the wines open up their flavors. The odors that can potentially develop as the wine sits in the bottle for long periods of time will also air out within a few minutes of aeration.
Although aeration has these advantages, it can often be detrimental to the quality of red wines that are older than fifteen years. They are more delicate and can easily lose their fruity taste. So, aeration is better suited for young wines while older wines are better consumed without aeration.
Aeration of a wine is possible through various methods; the easiest method is via the use of an aerator spout. This tool allows the wine being poured out of the bottle to mingle with oxygen as it manipulates the pour rate with the introduction of air. The classic method of aeration is done with the use of a decanter, usually a crystal vessel with a wide base that allows the wine greater contact with oxygen. If none of these tools is available, you can always swirl the wine in the glass to aerate it.
With older wines, it is best to stick with the air exposure it recieves after pouring it into a glass, as this provides sufficient contact with oxygen.