Researchers in France have shown that genuine Bordeaux wines can be distinguished from fakes by testing the minute quantities of lead in their composition.

Wines and indeed other foods and beverages tend to have low levels of lead, resulting from environmental contamination from natural or man-made sources that is taken up into plants.

Scientists have discovered that the amounts and ratios of elemental lead and lead isotopes can serve as a “fingerprint” that can determine the geographic origin of a wine – and be used to tell a genuine vintage from a knock-off.

Levels of lead in the atmosphere have been falling dramatically in recent decades since the use of lead as an additive in fuel has been banned. It’s been known for many years that lead isotope ratios can be used to identify the origin of wines as well as other foodstuffs such as milk powder.

The latest study puts the technique through its paces for a specific task – distinguishing genuine Bordeaux wines produced by prestigious vineyards over the last 50 years from wines bottled in China between 1998 and 2009. It is published in the journal Food Chemistry.

The researchers took 43 authentic red and white Bordeaux wines from the winemaking estates of Médoc, Graves and Libourne, and ran a comparison with 17 red wines sourced from China, including 14 labeled as ‘Bordeaux’ as well as three genuine Chinese brands. The suspect bottles were selected because they either had spelling mistakes in the names of the known wineries or claimed to be from non-existing producers.

They found that the levels of lead in the genuine French wines reflected the reduction in environmental lead seen since 1969 – the date of the earliest bottle tested – and all fell within recognised safe levels.

The suspect wines had levels that overlapped with those from the French group, but tended to have isotopes suggesting more of the lead came from man-made sources such as leaded gasoline than natural, background sources.

Moreover, a subgroup analysis for four suspicious samples said to be produced in Pauillac in 2004, 2005, 2006 and 2007 were compared directly with genuine wines from that period and found to have different isotopic profiles.

“Despite of limited number of genuine and suspicious samples, this test give a particularly compelling example of [lead] isotopes application to authenticity issues,” write the authors.

There’s an obvious limitation to the approach of course.

“If suspicious wines … would be produced in the same region as authentic, a clear identification by lead isotopes alone may be significantly hampered or even impossible,” they note.