One of the top wine questions on Ask.com is an issue that perplexes most wine drinkers: What does an aerator do?
For this one, though, I’d extend the question itself and also consider what a decanter does, because we’re essentially talking about the same thing, which is exposing wine to air in order to accomplish...something.
As for what that something is, it’s both simple and tough to wrap your mind around at the same time. Basically, we’re trying to ‘open up’ a wine when we aerate it in one way or another. And what we mean by ‘open up’ is best addressed as a question: Have you ever popped the cork on a bottle of wine, poured a glass, and felt as if the acid and tannins had some sort of Darth Vader-like death grip on the fruit? As if the wine itself was closed in on itself? (Picture how people hold themselves on a frigid winter day: Shoulders hunched up, elbows and hands curled into the torso, teeth gritted and muscles tense...)
By aerating a wine, we’re hoping to loosen it up, just like your muscles do when you finally get inside and sip a cup of hot chocolate.
It actually makes sense that some wines should be this tight: Even if it’s sealed with a cork (which is not perfectly air-impermeable), the juice in the bottle has essentially gone without much air except for the little bit of space between the top of the liquid and the bottom of the cork or screw-cap. It needs to breathe, which is what aerating or decanting it does. And depending on the wine, it might need a lot of air, a lot of time in the decanter. This varies by wine and by personal taste.
Sometimes, of course, old wines are decanted in order to pour the liquid off the sediment, but I’d caution you here: With very old wine, you risk showing it too much air and killing it. (It’s kind of like the wine equivalent of spending your entire life atop Mt. Everest and then, suddenly, taking an elevator down to sea level without acclimating: Could cause some problems, to be sure...) You might be better off just pouring individual glasses and allowing the wine to open up that way. Think of this as a bit of an insurance policy against over-aerating your wine.
The truth, though, is that most of us don't drink very old wine, and barring your being lucky enough to be offered, say, a 70-year-old Burgundy, aerate your wines to your heart’s--and your palate’s--content. It will almost always make your wine more approachable, softer, and ultimately more pleasurable.