Detecting wine forgeries – Brief Article
With bottles of rare vintage wines selling for thousands of dollars, wine forgery is becoming a very tempting criminal activity. Until recently, forgery has been very difficult to detect, let alone prove beyond reasonable doubt in a court of law. But science is coming to the rescue.
European chemists are developing ways of finger printing wine by measuring the occurrence of site-specific isotopes in wine samples, and at least one Australian wine company is planning to add a sample of DNA to the wine capsule for future authentication.
Now Graham Jones, a scientist at the University of Adelaide, has added another weapon to the armory of fraud detectors–the ability to accurately determine the age of wine in a bottle.
He says in the future European Union (E.U.) regulations may require full authentication of imported wines, including Australian wine, before sale.
“Down the track, the E.U. may require vintage certification,” he said. “We need to be prepared to provide that information if we are to continue to export wine to Europe.”
Carbon dating has been in use for many years to estimate the age of prehistoric artifacts. It works by comparing the proportion of [C.sup.14] isotopes to the much more common [C.sup.12] in carbon compounds. This is known as the [C.sup.14]:[C.sup.12] ratio.
This ratio remains constant in the atmosphere over thousands of years because losses of [C.sup.14] due to radioactive decay are balanced by the formation of new [C.sup.14] by cosmic rays. However, once carbon is incorporated into a solid object, such as a tree, the [C.sup.14]:[C.sup.12] ratio decreases slowly as a result of radioactive decay. Therefore, knowledge of the ratio between the two isotopes can be used to estimate the age of the object.
Jones says [C.sup.14] decays too slowly for carbon dating to be used to estimate the age of recent materials such as bottled wine. However, atomic bomb tests from 1945 to 1963 boosted the amount of [C.sup.14] in the atmosphere. Since 1963, this has steadily decreased due to dilution, as carbon is absorbed into plants or the oceans and more carbon is released as organic matter is burnt or decays.
This means that each year since 1954 has a particular [C.sup.14]:[C.sup.12] ratio and this ratio is locked into all carbon compounds photosynthesized in that year. Therefore it is possible to estimate the age of wine by comparing the [C.sup.14]:[C.sup.12] ratio in an unknown wine sample with the ratio found in a sample of known age. Jones says a calibration curve can be constructed using wine of known vintage, tree rings and historical records of atmospheric levels of [C.sup.14]
Because [C.sup.14] only occurs in the atmosphere to the extent of about one part in a trillion, an ultrasensitive mass spectrometer is required. Jones cooperated with Ewan Lawson and Claudio Tuniz of the Australian Nuclear Science and Technology Organization at Lucas Heights to develop mass spectrometry of wine.
Jones measured the [C.sup.14]:[C.sup.12] ratio of the ethanol component of a number of wines of known age and compared them to the [C.sup.14]:[C.sup.12] of the atmosphere. (See diagram on page 74.) He found a number of discrepancies; most discrepancies were small, of the order of six months, and may reflect naturally occurring differences in the [C.sup.14]:[C.sup.12] ratio from different locations. Most nuclear explosions took place in the Northern Hemisphere, but the data presented in Jones’ work was gathered in New Zealand, and more recently Tasmania, whereas the grapes used to make the wines came mostly from the Barossa Valley.
“At least one of the datapoints is uncertain,” Jones said. “The isotope ratio may have been affected by non-uniform mixing in the atmosphere.”
Will this evidence stand up in a court of law?
“That’s a good question. We need to develop protocols to prevent confusion over samples and to build up a large database of tested wines before we can say with certainty that a wine is of a certain vintage.”
Determining the age of wine is not so simple as just measurng the [C.sup.14]:[C.sup.12] ratio of one of its components. Old vintage wine may have been topped up with younger wine or older material may have been added. Some of these additions are legitimate and permitted under law.
To distinguish between legal and illegal additions, Jones suggests measuring the age of a range of wine components. For example, ethanol, tartaric acid and various phenolic compounds, which occur naturally in wine or are acquired from oak. The more wine components that are measured, the better the chance of detecting fraud.
“This process should detect deliberate attempts to mislabel wines,” Jones said. “Measuring the age of several components will make it very difficult to replicate an authentic wine.”
(Frank Smith lives in Perth, Western Australia. He specializes in corporate and science writing
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