1. Decanting a young wine allows it to "open up" and mellow out some of the harsher tannins, making them softer and the wine easier to drink.
2. Decanting an old wine allows the sediment--which has dropped out of the wine over time and ended up at the bottom of the bottle--to remain in the decanter when the wine is served (instead of on your teeth...). **Note: When serving an old wine, be sure to drink it soon after the bottle is opened and decanted. Oxidation can wreak havoc with old bottles in a very short amount of time. The wine can taste totally different at the end of the meal than it did at the beginning.
