You can use NMR to tell you if it’s still good, and now you can tell how old the bottles are by hitting them with an ion beam.

Nuclear Physicists Fight Wine Fraud

The beams, which are directed at the glass, not the wine, can distinguish how old the bottles are and where they might originate.
[…]
To prevent counterfeiters from filling authentic old bottles with ordinary wine, Williams intends to combine the ion beam test with another established method that checks for levels of a radioactive isotope, Caesium 137, in the wine itself.
This technique, however, is only effective in identifying wines made in the era of heavy atomic weapons testing in the latter half of the 20th century.

Mmmmm. Cs-137. I know that’s what gave last year’s Beaujolais Nouveau such a perky flavor.

Update: Jennifer Ouellette has a rather extensive post about wine fraud over at Cocktail Party Physics (though this is wine, and technically not a cocktail. But it’s some interesting history and more information. The New Yorker article she mentions is quite interesting)