WASHINGTON: Up to 5% of fine wines are not from the year the label indicates, according to Australian researchers who have carbon dated some top dollar wines.
The team of researchers think “vintage fraud” is widespread, and 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 – its vintage.
The test works by comparing the amount of carbon-12 and carbon-14 in grapes.
Grapevines accumulate carbon
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.
Carbon dating wine
For the study, researchers wanted to see if a wine’s vintage can be dated by looking at the ratios of carbon isotopes.
This is similar to the way that fossils or artefacts are dated, however this new method does not use the radioactive decay of carbon-14 into carbon-12, which has a half-life of thousands of years, to estimate the age.
Instead, the age is estimated from the known ratios of these isotopes in the environment from the years the grapes were grown.
Atomic bombs changed carbon content in grapes
“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 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 in turn changes the ratio of carbon-14 to carbon-12 in plants, like grapevines.
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.
They then compared the measurements to radioactivity levels of known atmospheric samples, and found they were able to reliably determine the vintage of wines to within the vintage year.
The researchers think carbon-dating fine wines could help nip in the bud the growing practice of vintage fraud.
According to the study, wine experts have estimated that up to 5% of fine wines sold today are not all they are cracked up to be on the label or in the price tag.
“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, that isn’t the right vintage year,” Jones said.
“Connoisseurs collect vintage wines and prices have soared with ‘investment wines’ selling for hundreds of thousands of dollars a case at auction,” he said.