Decanting vs. aerating are two words that people often use interchangeably when it comes to wine. While you can aerate a wine using a decanter, the two verbs are actually opposite actions.
When one decants a wine, the goal is to pour it as carefully as possible in order to minimize the amount of air that mixes with the wine. The purpose of decanting is to remove the sediment of the wine. As wine ages, the fruit aromas soften, the tannins link up and fall out of the wine (that’s the sediment) and the wine becomes more integrated, developing tertiary aromas such as earth, potpourri, or cedar. Older wines evolve very quickly when air hits them. The goal is to enjoy each phase of the wine as it is evolving, and in order to do that, one must minimize the amount of air that mixes with the wine. Never aerate an older wine. Never open it up and let it breathe. Decant out the sediment, then sip it, without swirling, and enjoy it as it evolves in your glass.
When one aerates a wine, the goal is to pour it energetically into the decanter and swirl it, in order to mix the wine with as much air as possible. The purpose is to soften the tannins and let the wine ‘open up’. It should only be done with very young, tannic wines such as a three year old Bordeaux or Northern Rhone Syrah. Syrahs from the northern Rhone are so tannic, some are co-fermented with Viognier to soften the tannins. As a general rule Napa Cabs are sold ready to drink as are most new world wines. And many European wines are held from market until they are ready to drink. For example, while Tempronillo is a tannic grape the reservas must be aged a minimum of three years before they are released and the grand reservas are held for five years. Many Italian wines such as Borolo and Brunello also have very strict aging requirements.
Most wines do not need to be aerated because by the time they come to market they are ready to drink. Only very young, very tannic wines will need aeration. And only very old wines need careful decanting.

