Study uses carbon-dating to check wine vintages
Ever paid top dollar for a bottle of wine that says on the label it's from a much-sought-after year, only to find that it tasted like cheap, non-vintage plonk? Well, a team of scientists in Australia, who think "vintage fraud" is widespread, have come...
Ever paid top dollar for a bottle of wine that says on the label it's from a much-sought-after year, only to find that it tasted like cheap, non-vintage plonk?
Well, a team of scientists in Australia, who think "vintage fraud" is widespread, have come up with a test that uses radioactive carbon isotopes left in the atmosphere by atomic bomb tests last century and a method used to date prehistoric objects to determine what year a wine comes from, or its vintage.
The test works by comparing the amount of carbon-12 and carbon-14 in grapes.
Both are isotopes of carbon and are captured by the grape plants when they absorb carbon dioxide, the main nutrient used by living plants in their growth cycle.
Carbon-12 is the main isotope in the carbon absorbed by the grapevines, and is very stable, while only tiny amounts of carbon-14, a radioactive isotope, are found in the plant. The amount of carbon-14 has varied over the years, too, which makes it a useful tool for judging the true age of a wine.
"Until the late 1940s, all carbon-14 in the Earth's biosphere was produced by the interaction between cosmic rays and nitrogen in the upper atmosphere," said Graham Jones of the University of Adelaide.
"This changed in the late 1940s up to 1963 when atmospheric atomic explosions significantly increased the amount of carbon-14 in the atmosphere," said Dr Jones, who led the study and presented its findings at the annual meeting of the American Chemical Society, held in California.
More and more fossil fuel has been burnt since the bomb tests stopped in the 1960s and this has had the effect of diluting the radioactive carbon-14 in the atmosphere.
That is turn changes the ratio of carbon-14 to carbon-12 in plants, like grapevines.
For the study to see if a wine's vintage can be carbon-dated, much in the same way that fossils are, the researchers measured the carbon-14 levels in the fermented sugars that give wine its alcohol content, in 20 Australian red wines from vintages from 1958 to 1997.