'Bomb pulse' in grapes harvested since atmospheric tests can be dated to within a year

This article is more than 10 years old

This article is more than 10 years old

The following correction was printed in the Guardian's Corrections and clarifications column, Wednesday 24 March 2010

This article about traces of radioactive carbon being found in wine said that the last atmospheric atomic bomb tests took place in the 1960s. That is true of American nuclear tests, but France carried on testing in the atmosphere until 1974 and China until 1980.

A trace of Bikini atoll could join hints of black cherry and complex citrus notes in the sommelier's lexicon for describing fine wines, research has suggested.

Harmless amounts of radioactive carbon have been found in wines made from grapes harvested since the last atmospheric atomic bomb tests were carried out in the 1960s.

But the "bomb pulse" of radioactive carbon lingering in the alcohol of wines produced since could be a good thing for wine dealers and collectors.

Scientists have been able to pinpoint a wine's vintage to within a year by analysing the levels of radioactive carbon in the wine, a technique they say could help detect fraudulent attempts to repackage cheap plonk as a high-end tipple.

Last month, a group of French wine dealers were charged with conning leading US winery E&J Gallo into buying 18m bottles of plonk repackaged as pinot noir.

Some experts claim that around 5% of fine wines currently being sold are faked, either by being diluted with cheaper wines or sold under false labels.

The fraud is driven by the extraordinary prices commanded by top-quality wines. A case of Chateau Lafite Rothschild 1982 – which cost £2,613 in 2000 – sold for more than £25,000 last year.

"The problem goes beyond ordinary consumers being overcharged for a bottle of expensive wine from a famous winery with a great year listed on the label," said Graham Jones, of the University of Adelaide. "Connoisseurs collect vintage wines and prices have soared with investment wines selling for hundreds of thousands of dollars at auction."

The wine industry has introduced special seals and labels in an attempt to frustrate fraudsters, but Jones believes analysing a wine's bomb pulse may give people more confidence that they have not been conned.

Almost all the carbon dioxide in the atmosphere contains the stable carbon-12 form of the element. Each atom of carbon-12 has six neutrons and six protons in its nucleus. But atmospheric atomic bomb tests, which ended in 1963, released vast amounts of radioactive carbon-14 into the air. A carbon-14 atom has two extra neutrons.

When grapes grow on the vine, they absorb carbon dioxide, which contains both stable carbon and traces of radioactive carbon-14 left over from bomb tests, from the air. As time goes by, carbon dioxide emissions from fossil fuel burning dilutes the amount of carbon-14 in the atmosphere.

Speaking at the American Chemical Society annual meeting in San Francisco today, Jones said his team had been able to date wines by measuring the relative amounts of carbon-12 and carbon-14 in the alcohol produced from the grapes.

"The year that the grapes were grown fixes the age or vintage of the wine," he added.

The scientists analysed 20 Australian reds with vintages from 1958 to 1997 and compared their levels of radioactivity with calibrated sources of radiation.