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new test can identify what grapes are in your wine [12-01-2011]

When a wine label reads “Merlot,” most consumers believe that’s what’s inside, but while scientists can genetically identify grapes, there hasn’t been a way to ID grape varieties in a finished wine. But now an ongoing medical study at the University of Texas may have found a solution that could give the wine industry a new tool in authentication. Scientists at the university, with help from colleagues at the University of California at Davis, have developed a sensor that can identify grape varieties in wine by measuring and identifying the tannins.

Dr. Eric Anslyn and his team of undergraduate research students have created receptors that respond to tannins in different types of grapes. The process involves placing a combination of chemicals on display plates with 96 separate wells. The team then adds samples of wine to these receptors. “The receptors change color when we apply mixtures of tannins,” said Anslyn. Using a computer program to analyze the results, the team tested different types of red wines and found that the tannins produce different recognizable patterns. “It really relates to the DNA coding of the wine.”

The group chose to study red wines since they have the most tannins. They tested varietals, including Zinfandel, Cabernet Sauvignon, Pinot Noir, Shiraz and Gamay, from various producers. White wines were not included in the test, but Anslyn believes that the procedure can distinguish between white grapes since they contain tannins as well.

For years, scientists and producers have had to rely on other methods to identify grapes. “With fresh [grapes] you can do genetic analysis,” said Dr. Andrew Waterhouse, viticulture and enology chair at U.C. Davis. But there have been no tests that can identify varietals once they go through the winemaking process. “When you look at wine, the DNA is broken down so much that, so far, no one has been able to capture the DNA [of the grapes] from finished wine.”

According to Anslyn, the study’s goal was not to produce a tool for the wine industry. The undergraduate team was attempting to create a device that can mimic mammals’ senses of taste and smell to create diagnostic solutions for diseases. They wanted to analyze tannins. “The real basis of this work is to prove that technology can distinguish mixtures of chemicals and where they come from,” Anslyn said. He decided to study wine because of its complexity and because people are interested in it.

There are limits to the technique, however. It can’t determine the provenance of the wines, and obviously the wine must be opened to be tested. “With the limited set of wines we studied we could tell one varietal from another with some outliers,” said Anslyn. So far the error rate for the test is still unknown. Anslyn also said that the process has not addressed wine blends or aged wines though he is certain that there will be a point in the future when they will be able to authenticate both.

The method could prove useful—when wine companies purchase bulk or already bottled wines from another producer they have few ways of verifying the wine’s grape varieties. And while the technique is still in its early stages, it could become a tool in helping wine companies authenticate counterfeit bottles. Counterfeiters have been known to make knock-off labels of premium brands and attach them to inexpensive bottles of wine or mislabel wines with different grape varieties. The test could help organizations like the Alcohol and Tobacco Tax and Trade Bureau (TTB), which checks for improperly labeled wines. “We are interested in any viable approach that can reliably determine the varietal authenticity of wines,” said Tom Hogue, a spokesman for the TTB.

Bron: WineChina.com