Definition: Decanting or aerating

Decanting is the noble act of separating the sediment (i.e. the solid particles) from the wine itself. In short, it is a form of filtration.

Decanting is simply the act of aerating wine by exposing it to air so that the wine (often young) can develop and mellow.
Be careful with very old wines before decanting them. This act, as noble as it may be, can denature, shock or even kill the wine.

The misconception
Under the pretext that the wine is old, it must inevitably be decanted because there is a deposit. So, we decant it...
This is a mistake that can be very costly.
Let's imagine a wine, at random. A 1969 Vosne-Romanée. As this wine is old, we open the bottle, decant it by candlelight and leave it to rest for 10 minutes.
Problem
Decanting mainly involves the wine undergoing very sudden and violent oxygenation.
However, this precious, aged wine has been sealed in its bottle for 36 years in this particular case. And God knows that this capricious elixir needs calm, serenity and respect.
If you proceed in this manner, by decanting it, its lifespan will become very limited due to the violent act of oxygenation. Half an hour later, very little will remain, and your memories will be blurred.
When should you decant an old wine?
An old wine can be decanted, and therefore withstand this act, provided that it is built for it.
It must have a very solid, powerful architecture, an opulent structure, and tannins that are still present, even firm.
In other words, a very great wine from a very great vintage. Bordeaux wines, the great wines of the Rhône Valley. In short, exceptional vintages.
And decanting?
Decanting simply consists of pouring the wine into a carafe in order to settle it. It is mainly practised for young red or white wines. These wines are often still somewhat uneven, their elements still a little scattered.
These wines need to be shaken up a little to make them more appealing.
Like a slap on the bottom given to a naughty child, this act allows the wine to settle down, ultimately making it more approachable.
Any young wine with a rich, complex structure, such as sunny southern wines, should be decanted. The same applies to white wines.
Please note
Pinot Noir grapes from generic appellations (Burgundy, Hautes Côtes de Nuits, etc.) do not tolerate oxidation very well. Avoid decanting them.
The alternative
Ideally, a wine worthy of interest should be opened 6 to 12 hours in advance for the most prestigious ones, i.e. at room temperature. Let them breathe in your cellar at 13°C.
You will find that this infinite patience and respect for your bottles will reward all your efforts. This slow, natural oxygenation gives the wines a wonderful comfort, which they will return to you.
Source: Emmanuel Delmas, sommelier