Wine is alive; between bottling and drinking we can visual it as being in a sort of hibernation, during which it spends several years shut in a bottle and stored in the dark. Once uncorked it is easy to understand that it needs some time and, above all, some air in order to awaken its finest bouquet.
This is why old wine has to be decanted, a fascinating operation which, according to the rules, ought to be done with a transparent carafe (the decanter) and a candle. After the bottle has been left in a vertical position it is important to be careful, pouring the wine slowly, controlling its flow by the light of the candle. As soon as there is any sign of the deposit moving, pouring stops. In the wide-bodied carafe the wine has a chance to breathe for twenty or thirty minutes.
For wines which are very old (twenty years or more) things are done differently as such rapid oxygenation could be too much of a shock for the wine and immediately destroy its character. In this case it is better to wake it up slowly, by pouring it directly into wide-bodied glasses (known as balloons).