The World of Wine

Can chemical analysis confirm a wine's authenticity?

There’s a romance to wine unmatched by most agricultural products. Making wine, with all its complex flavors, remains as much an art as a science.

When grapes stay on the vine, their sugar content increases, as does the concentration of phenols, organic compounds that contribute to the wine’s color and body.

Hints of citrus, peach, raspberry, pear, oak, grass, or flowers may show up in the taste or smell of wines. The catalog of factors that determine the flavor and bouquet is almost as long as the list of adjectives that connoisseurs use to describe them.

Rain before the grape harvest, for example, bloats the fruit and makes the wine’s flavor less intense. Long growing seasons enable rich, complex tastes to develop. The slope of the hill where the grapes grow, its drainage, and the amount and intensity of sunlight that the vines receive all affect the taste of the grapes.

Even after the grapes are picked, vintners face an array of choices for fermenting the sugar into alcohol. Different species of yeast can change the flavor, as can the length of time the grapes are fermented. Finally, winemakers must decide whether to age their product in stainless steel vats or oak barrels.

All these steps from vine to bottle vary the mix of organic molecules that give wines their distinctive flavors. Yet many wine experts, especially in Europe, trace the richness of a wine quite literally back to its roots. A vineyard’s particular combination of soil, rock, and geography— its terroir—is the most significant aspect of a wine, they say.

Now, science is examining terroir for both pragmatic and romantic reasons. It’s asking whether chemical analyses can help authenticate where a wine was made and pin down the elusive nature of terroir.

Championing terroir

Europeans are the strongest champions of terroir. In France, most wines are distinguished by the region in which they are produced, such as Champagne. As the year 2000 approached, for example, many people wanted to buy sparkling wine for New Year’s Eve celebrations. “This big market led to many attempts to misrepresent [other] sparkling wines as champagne,” says Dominique Tusseau, a scientist with the Interprofessional Committee for Champagne Wines in Epernay, France.

With a premium attached to wines from a specific region, “there are compelling legal reasons to be able to identify the terroir,” says Robert M. Pool, a grape specialist at Cornell University. While “the [tested] elements may or may not be responsible for the special characters of the wines from a given region, creating an effective [chemical] ‘fingerprint’ will ensure that the production is from the region listed on the wine label,” he says.

Laws around the world regulate the purity of wines. “German wine law does not allow you to mix wines,” says Wolfgang Todt of the Max Planck Institute for Chemistry in Mainz, Germany. “If a winery is taking cheap wine from the Mediterranean and diluting [its finer wine with it], then it is cheating the people paying a higher price, even if they cannot taste the difference.”

Chemical analysis is not new to the industry. Government inspectors test wines to identify unhealthy contaminants, such as lead, and to ensure that wines haven’t been adulterated with water, sugar, or artificial colors.

U.S. winemakers have also looked to chemistry to identify the critical elements in wine and learn how to use them to produce high-quality wines, Pool says. “For the producer of an established wine type . . . it is important to understand which elements are critical to achieving and maintaining the identity and quality of its wines,” he says.

Already, chemical testing of wine has helped identify “the common characters of wines, so that reliable and palatable wines—the Cokes of the wine world—can be made and marketed at a reasonable price,” says Pool.

Scientists have known for almost a decade that analysis of various chemical elements in wine can help roughly identify the geographic origin of wines, but the tests have been too complex and not conclusive enough to be used on a large scale.

Chemical fingerprints

Improved analytical instruments and powerful computers are now enabling scientists to better determine a chemical fingerprint for products of each wineproducing region. For the past few years, for example, a coalition of the French government officials and local growers has collected samples of all the wine produced in the small Champagne region, Tusseau says.  The group can now analyze—for as many as 100 organic compounds and elements—potentially mislabeled champagnes and compare them with these standards. This has helped the region put a dent in the serious problem of misrepresented champagnes, Tusseau says.

German researchers recently studied 165 wines from six grape-growing regions. The team showed that the differing proportions of 15 chemical elements, such as aluminum and calcium, can correctly distinguish wines from particular regions with 70-100 percent accuracy.

Testing for just three elements—barium, silicon, and vanadium—and three organic com-pounds, the researchers correctly identified the geographic background of as many as 90 per-cent of the wines tested, they reported in the October 1999 American Laboratory. The organic compounds they tested reflect wine-making procedures: 2-furancarboxaldehyde, whose content is determined by aging; 4-methyl-1-pentanol, the amount of fermentation; and 1-octanol, the wine’s maturity.

It would be laborious to routinely identify the geographic origins of wine in this way, admits chemist Gabriela Thiel of the Institute of Inorganic and Analytical Chemistry at the Friedrich Schiller University in Jena, Germany. “Temperature and the amount of rainfall fluctuate over the course of several years and within growing periods, so intake of trace elements from soil into grapes varies slightly from year to year,” she says.

In addition, techniques of wine processing tend to vary from region to region, she says, and these differences could also affect the proportions of trace elements found in wines.

A slightly simpler approach might be to measure traces of strontium in wine to track its origin, says Todt. In the soil over time, atoms of another naturally radioactive element called rubidium decay into a form of strontium that can be distinguished from other isotopes of strontium that are present. Just as the ratio of different chemical elements varies in the soil, grapes, and wine from region to region, the ratio of these isotopes of strontium to rubidium and each other varies as well, says Todt.

He and his colleagues have looked at about 60 different vineyards in Europe and Australia. They find that all grapes growing in the same soil have the same strontium composition and that the strontium-isotope ratio varies widely among soils, and therefore grapes, around the world.

“This is simpler than multielement analysis and as accurate in predicting a wine’s origin,” Todt says. One advantage of the test is that the processes of fermentation and aging don’t alter the strontium-isotope ratios in grapes and wine. Another advantage is that the type of grape used to make the wine doesn’t affect the result, he says. Some fertilizers, however, may add strontium to the soil and thus alter the isotope ratio found in grapes and wine.

Todt says that for now, his team’s analyses are “just too expensive to be routine,” but he expects that the cost of the equipment used to measure isotopes will come down within 5 years.

Neither elemental analysis nor isotope measurements are foolproof, Todt says. “For unambiguous determination of the origin of a wine, we will probably need several analytical methods,” he says.

The eventual development of national or even international registries of typical soil and wine compositions for different regions will aid authentication efforts and make it easier to prove that a wine was not grown and made in a particular region, he adds.

Quirky regionality

“People are so interested in terroir [because] wine is one of the few things that haven’t become so homogenized it can be ignored rather than appreciated,” Pool says.

“The beauty of wine is its quirky regionality,” agrees Leo McCloskey of Sonoma-based Enologix, the largest wine-consulting firm in California. “Even those of us in the wine business are susceptible to its mysterious allure.”

Can the effects of terroir be scientifically documented? McCloskey believes that for a few California regions the answer is yes. A few years ago, he and his colleagues showed that chardonnays from Carneros, Calif., tended to have more intense citrus and green-apple flavors than other chardonnays, he says. An earlier study suggested that pinot noir wines from the Carneros area tend to have notes of cherry and spice not present in other Napa Valley wines.

From his work at the National Institute of Agronomical Research near Angers, France, Gérard Barbeau concludes that wines made from the same kind of grapes, grown in the same region using identical practices but in slightly different terroir, harvested at exactly the same time, and made into wine in exactly the same ways, still can be remarkably different. Some wines may be sweeter or more astringent than others; the color intensity may differ; the types and intensity of aromas may vary. These underlying differences, he says, must be due to terroir.

“The quality of the raw material is of paramount importance,” Barbeau says. “The variability induced by the physical characteristics of the terroirs is much more important than everything else.”

Not everyone agrees. In a study published in the May 27, 1999 Food Quality and Preference, German researchers found that among 20 Rieslings rated for odor, flavor, and body, the groupings of similar wines depended as much on the year that the wine was made and the winery that produced it as on the grapes’ growing area.

A classification system based solely on geographic origin of a wine “would be rather confusing for consumers,” says U. Fischer of the State Agricultural College and Research Center in Neustadt an der Weinstrasse, Germany.

Accurate labeling

The U.S. Bureau of Alcohol, Tobacco, and Firearms (ATF) is examining ways to test whether a wine is from the region it claims on the label. “One of our mandates is to make sure that the products we regulate are accurately labeled,” says Richard Gahagan of the ATF bureau in Fresno, Calif. “We take it very seriously. Regardless of the eventual taste of the wine, the consumer is entitled to get what they think they are buying.”

Unlike European wines, which are closely regulated by region, most U.S. wineries don’t face rules that they must make wines only from grapes in a single field or a small vineyard, and therefore their products’ taste is unlikely to reflect terroir.

Moreover, merchants identify most American wines by the kind of grape, such as chardonnay or pinot noir, used to make the wine. Such a category can encompass products of more than one vineyard, and a single bottle can contain wine made from grapes grown in different areas.

As American wines become more widely known, however, the wine industry is beginning to realize that people may prefer to buy a wine from a certain location, such as Sonoma or Napa Valley, says McCloskey. If wines from a region taste similar, and the label fully informs buyers, consumers have a better chance of choosing a new wine they like, he notes. Yet some geographic areas mentioned on a bottle label may say nothing about the taste.

“Since it is so hard to describe wine and define terroir to the consumer, wine can be a big mystery,” McCloskey says.

“Testing [of wine] might protect you from buying a fraud, but it may not help you pick a wine which tastes any better,” cautions Andrew L. Waterhouse of the University of California, Davis.

So, what’s a wine lover to do? Perhaps just wait to see whether scientific, chemical analyses will be used to characterize and evaluate wines.

The art of winemaking is here to stay. It’s possible, however, that long before the next millennial celebration rolls around, wine and champagne drinkers may be able to toast in the new year with wine that’s not only carefully crafted but chemically authenticated.

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