What is the main reason for decanting a bottle of wine?

Decanting a bottle of wine primarily serves the purpose of aeration, which helps the wine to 'open up' and express its full range of aromas and flavors. When wine is poured into a decanter, it is exposed to air, which promotes oxidation. This process can soften tannins, especially in young red wines, and enhance the overall profile of the wine. Aeration allows volatile compounds to evaporate, allowing the more pleasant, aromatic components to rise to the surface, making the wine more expressive and enjoyable.

This contrasts with the other options. Increasing acidity is not typically a goal or a benefit of decanting; in fact, most wines have a balanced acidity that should be preserved. Reducing alcohol content is not achieved through decanting, as the process does not affect the alcohol level in the wine. While some sediment may be present in older wines, decanting is not primarily intended for freezing or removing sediment but rather separating it from the wine during pouring if necessary. Thus, the primary goal and benefit of decanting remain focused on the aeration of the wine.