From the December issue of GQ: As with everything in wine, decanting is more complicated than you think. Yes, pouring wine out of its bottle into a specially designed container adds a special flourish to a fine dining experience. And yes, it helps separate old wine from any sediment that has formed in the bottle.
However, as a means of promoting aeration in young wines, particularly reds, decanting is controversial. Your old man probably told you that decanting will cause: 1) the wine’s bouquet to “open up” (allow the wine’s full array of aromas to show) and 2) the wine to become less austere in terms of structure (tannins will become softer and rounder) but unfortunately there is very little science to support this.
Decant a wine and you will indeed be saturating it in oxygen but oxidation reactions (at play in wine maturation and which lead to fine wine becoming both “smoother” and more complex over time) take much longer than the usual hour or two between decanting and drinking. Decanting as a way of amplifying oxidation towards prematurely and agreeably ageing wine just doesn’t hold up.
So why is aeration via decanting considered so important by so many? The only substance other than grapes traditionally added to make wine is sulphur, used as both a preservative and disinfectant. Excess sulphur additions can obscure a wine’s fruit aromatics and leave it stinking of either sulfur dioxide (burnt match), hydrogen sulfide (rotten egg), or mercaptan (sweaty armpit). In young wines, these stenches often are volatile and not chemically bound in solution so some aeration can alleviate the problem.
Essentially, however, the action of oxygen dissolved in a sound wine is detrimental in strict oenological terms – the longer before serving a wine is decanted, the more diffuse its and the less marked its sensory attributes.
Now you know the facts of the matter. Decanting is however hardly going to ruin a wine and if you want to indulge in a little bit of showmanship next time your mates come around for dinner, then decant away.