The Coravin is a completely different story. In fact, if you want to drink part of a bottle of wine and keep the rest in absolutely perfect condition, the Coravin is really the only way I've ever come across to do it. The downside is the price: $299. But the upside—assuming you're a serious wine lover, or someone buying a gift for a serious wine lover—is substantial.
The results were clear. Of the three most familiar methods, putting the half-finished bottle of wine in the fridge is best. Gassing it is second best. The pump is the worst, and in some cases actively detrimental, as the vacuuming process seemed to suck out the aroma of the wine, too (I tried several models of pumps, with the same negative results each time). But the most effective method was a combination of gassing the wine and putting it in the fridge. Even a delicate white, like J. Hofstätter's aromatic 2012 Pinot Grigio, lasted at least a week this way. While not quite as bright and fresh as a newly opened bottle, after seven days it was still a pleasure: peachy and crisp and all-around delightful.
The key thing about the Coravin is that it isn't a wine-preservation device at all. It's a wine extractor, or "accessing tool," as Greg Lambrecht, the medical-device inventor and wine collector who created it, says. A sleek black-and-silver gadget, it clamps around the neck of a wine bottle, then inserts a long, thin, hollow Teflon needle through the cork. Argon, an odorless, neutral gas that has no effect on wine, is pumped through the needle into the bottle. The increased pressure then pushes wine back through the needle and into a glass. The groundbreaking part is that, since the cork is never removed, no oxygen ever comes into contact with the wine.