Atomic bombs changed carbon content in grapes
Credit: Wikimedia
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.
Carbon dating reveals vintage fraud in wines
That's idiotic. Carbon 14 dating cannot be accurately used to "date" things that young. It's got a half-life of 5700+ years! Generally there's an uncertainty of at least ±30 years, if not more!
http://en.wikipedia.org/wiki/Radiocarbon_dating
Carbon Dating (C14:C12ratio) used for wine fraud
Read the paper. It is based on uptake and atmospheric composition, not on C14 decay.
Read TFA
The dating method, from what can be inferred from the web page, was not Libby's exchange method, but rather correlation with known changes of C-14 concentrations in the recent past. It could have just as easily have been done with any other detectable chemical/isotopic artifact whose concentration changed significantly on a time scale of years, as long as it would be proportionally incorporated into the grapes and from them into the wine.
Read the article before commenting?
If you had read the article you comment on you had understood how the dating in this case works. But obviously you are to clever to understand the simple and clever idea of the researchers ;D
First comment - fail
So keen to be the first commentator, they only read the headline!
did you not read the whole
did you not read the whole article
Re: "That's Idiotic"
Read the story before pronouncing!
This is not radiocarbon dating by radioactive decay.
This is based upon the INPUT proportions of C14 and C12, since across different years (due to processes described in the story) the proportions in the atmosphere have varied. The atmospheric proportion will reflect the proportions found in the wine accurately - in this case precisely BECAUSE of the long half-life....
Other potential sources of carbon....
The article said sugars, so I'm assuming any oils from the cask are separated out, so don't influence the results.
How uniform is the distribution of carbon isotopes in the atmosphere? Could a strong northerly wind change the local conditions sufficiently to give a different dating? And how long would it take for the carbon to regain equilibrium after a nearby forest fire?
And how do you account for chaptalisation -- added sugar? Even if you know the vintner had added sugar to the must, you'll not have a date of origin for the sugar, which could bias the results quite significantly, even if very little sugar is used.
The article is misnamed ....
The article is NOT about 'carbon dating' as the term is normally/usually used in science, where it applies to measurements of radioactive decay.
Perhaps 'atom uptake ratios' would be more descriptive...
Not Idiotic, but maybe not that ground-breaking either
I came to this article prepared to disbelieve the whole concept but I am (mostly) convinced. The method described is probably a reliable way of dating vintages from Australia, it may even be a reliable way of dating vintages everywhere. I, for one, would like to see how local and semi-local sources of radioactivity (Chernobyl's spotty effects across Europe, Three Mile Island and Hanford in the US, French reactors) do or do not affect the method. Is it equally valid for Chilean? Californian? Western Canadian? Israeli? French? other? wines as for Australian ones? Do the assumptions hold up regardless of source.
Without that material, this item is in danger of being little more than marketing propaganda for Australian wines as opposed to all others. I said, "in danger of" -- the points it raises are valid even if they are open to questions of translocality. I looked in vain for a link to the actual report here. Has anyone read it? Does it cover these issues?
It's quite interesting to see a method for dating things that's often (whether validly or not) questioned for its validity used in a way that bypasses all the problems usually raised against it.