How far in advance of drinking should I open red wine to let it breathe?
How messy are you prepared to get? A long time ago I dated a guy who had the mortifying habit, when dining at expensive restaurants, of placing one palm over a glass of freshly opened red and shaking it like he was auditioning for the Tom Cruise part in Cocktail. Then he would wipe his dripping hand on his table napkin, take a sip and exclaim over how well the wine had ''opened up''. It was an emergency CPR method of getting wine to breathe that required no advance planning. Even though it worked (and I ended up marrying him), I think asking to have the wine decanted might have been a mite less embarrassing.
If you're at home, you can open the wine an hour or three before you plan to drink it but don't expect it to do much to aerate the wine. The surface exposed to air is so small that it's unlikely to make a lot of difference. Pouring the wine into another vessel - from a height, if you have good aim and like drama - is much more effective.
Before you embark on the whole ''breathing'' thing, think about whether your wine needs it. A big, bold, young wine - a South Australian shiraz, for example - might taste tough when freshly opened and will generally benefit from air. Some wines like this can taste better after a day of being open. But a more refined wine of similar youth - for example, a pinot noir - is unlikely to need or want more air than it gets from simply being splashed into a glass.
As a rule of thumb, the older and more delicate a wine is, the more quickly it will deteriorate after being exposed to air. A wine bottled under cork may have been breathing - albeit slowly - for years. Once the cork is pulled and the wine is poured, its remaining fruit aromas can dissipate fast. If you have a special old bottle (more than about 10 years) and you're in doubt, don't open it too early - instead, pour a quick glass for yourself before deciding whether to decant.
To complicate things, aeration isn't the only reason to decant red wines: some wines drop a crust of sediment and can be decanted to avoid getting particles into the glass. If you've decanted for this reason and the wine is old, drink it sooner rather than later.