There are several ways that one might produce a counterfeit version of a rare wine. Probably the simplest is to make a phony label and capsule and place them on a bottle of another wine. Alternatively, one can take an empty bottle of a rare wine and fill it with something not so rare. A third option is to actually concoct a fake wine—for instance, to blend together several different wines, or several vintages of the same wine, or to combine a wine with a non-vinous flavoring agent. Wine sleuths have become reasonably adept at recognizing the outward clues that indicate a wine might be a knockoff—the labels, capsules, and corks often give fraudulent bottles away.

However, our ability to determine what is inside those bottles is limited. Carbon dating can reveal whether or not a wine was manufactured before or after the dawn of the nuclear age. Nuclear testing in the 1950s and '60s caused a spike in the amount of carbon-14 in the atmosphere, and if a wine has high levels of this radioisotope, it is an indication that some if not all of the liquid originated during or after that period. Cesium 137 is another marker: It is a radioisotope produced by nuclear fallout, and its presence can likewise peg a wine to the second half of the 20^th century. If a Bordeaux that is purportedly from the 1920s shows traces of cesium-137 or elevated amounts of carbon-14, that could well mean the wine is bogus. (It could also suggest a less nefarious possibility: The château might have recorked the bottle at some point in the past and topped it off with a younger vintage.) Testing for cesium-137 has one important advantage over carbon dating: It doesn't require opening the wine. Instead, it can be done using a gamma-ray spectrometer.

But Philippe Hubert, the French physicist who pioneered this method of evaluating wines, says that even if a wine is found to contain cesium-137 or higher concentrations of carbon-14, there is no way of knowing the precise year it was made, and if it doesn't contain either, there is no way of scientifically determining by how many years, decades, or even centuries it predates the nuclear era. Nor does the presence of cesium-137 or carbon-14 offer any hint as to where a wine was made. If a wine is a fake, figuring out what exactly is under the cork is a matter of guesswork. If a bottle of 1945 Mouton Rothschild has been filled with a $10 Australian Shiraz, an experienced taster should certainly be able to sniff out the fraud and may well deduce that the wine is New World plonk rather than a historic Bordeaux. But other phony wines may not be so easily unmasked. It is widely believed that some of the fake wines on the market have been fabricated by individuals who are themselves wine connoisseurs and who have a talent for producing counterfeits that can fool even the most discriminating palates.