Carbon-dating wine to sniff out fakes

Physics Today : Two decades of atomic bomb testing in the atmosphere are yielding an unexpected bonus for wine merchants concerned about fake vintages. Graham Jones from the University of Adelaide , Australia and colleagues reported yesterday at the American Chemical Society (ACS) annual meeting in San Francisco, California, a new radioactive carbon test to determine whether that Bordeaux or burgundy is from a fine vintage year and commands premium price or actually is a counterfeit wine worth much less.Fake wine is “an ongoing problem,” says Jones, with some wine experts estimating that up to 5 percent of the fine wine sold today is fake."The problem goes beyond ordinary consumers being overcharged for a bottle of expensive wine of a famous winery with a great year listed on the label,” Jones pointed out. “Connoisseurs collect vintage wines and prices have soared with ‘investment wines’ selling for hundreds of thousands of dollars a case at auction."Jones said the wine industry is fighting forgeries with special seals and high-tech labels. The method for authentication of a wine’s vintage may provide added confidence that the vintage on the label is the vintage in the bottle. A ‘hot’ grapeThe new vintage-checking technique is similar to radio-carbon dating, used for years to estimate the age of objects up to 68,000 years in the past. It works by comparing the amount of carbon-14 (C ¹⁴), a less common form of atmospheric carbon, to carbon-12 (C ¹²), which is more stable and abundant.The ratio of these two carbon forms, or isotopes, has remained constant in the atmosphere for thousands of years."Until the late 1940’s all carbon-14 in the Earth’s biosphere was produced by the interaction between cosmic rays and nitrogen in the upper atmosphere,” Jones says. “This changed in the late 1940’s up to 1963 when atmospheric atomic explosions significantly increased the amount of C ¹⁴ in the atmosphere. When the tests stopped in 1963 a clock was set ticking—that of the dilution of this “bomb-pulse” C ¹⁴ by CO ₂ formed by the burning of fossil fuels."Traces of radioactive carbon—including with recent vintages the “bomb-pulse"—are captured by the grape plants through the absorption of carbon dioxide and eventually transformed into alcohol and other carbon-based components of the wine."The year that the grapes were grown fixes the age or vintage of the wine,” Jones says."The carbon-14 isotope ratio of the wine alcohol can therefore be used to determine the vintage of a wine."An accelerator mass spectrometer was used to determine the C ¹⁴ levels in the alcohol components of 20 Australian red wines with vintages from 1958 to 1997 and the measurements compared to the radioactivity levels of known atmospheric samples. They found that the method could reliably determine the vintage of wines to within the vintage year.In addition to testing alcohol, measuring the age of other wine components, such as tartaric acid and various phenolic substances, can help improve the reliability of the technique for detecting fraud, Jones notes.Paul Guinnessy Related link How atom bomb tests could help detect wine fraud The Guardian Carbon-dating wine can spot fake vintages: research The Daily Telegraph