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A Chemical Explanation for Terroir?

A new study could explain why wines from neighboring vineyards can be so different
Photo by: Courtesy of Far Niente
Dozens of Far Niente's vineyards were used in the microflora study.

Posted: Jun 22, 2016 1:15pm ET

The wine world takes it as a given that a wine's characteristics depend at least in part on the place where its grapes were grown. It's the cornerstone of terroir, the French notion of the primacy of place.

What we don't know, however, is what exactly creates this sense of place in the finished wine. Some say it's the soil, but no trace soil elements have been detected in a finished wine. If it's climate, elevation, the tilt of the slope or exposure to the sun, how can two adjacent vineyards produce notably different wines?

Researchers at the University of California at Davis found some tantalizing clues when they took an extensively detailed look at the microflora that came in on the grapes from 40 different Northern California vineyards and compared them with the chemicals naturally produced in the finished wines.

They isolated thousands of specific bacteria, yeasts and other microflora from 40 individual vineyards before and after fermentation at Far Niente winery in Napa Valley in 2011. Two big takeaways: First, the patterns in which these occurred were distinct to each site. And, after analyzing all the data, they could predict the finished wines' patterns of metabolites (bacteria and other substances formed by fermentations) with 80 percent accuracy.

An earlier U.C. Davis study had identified patterns of bacteria from one viticultural area to another that could explain chemically "why there's such a thing as regionality," said one of the study's authors, David Mills of the U.C. Davis Department of Food Science and Technology. This new study shows that the wines made from individual vineyards not only exhibit similarly individual patterns, but those patterns are predictable based on the microflora in the vineyard.

These patterns could explain "why Malbec from Argentina tastes different from Malbec from California," Mills said, "and why Chardonnay from a vineyard in Carneros tastes different from one in Russian River Valley."

This study used high-tech tools to survey "all the chemical species in each example of unfermented juice and in the finished wines made from them," he said. Being able to predict the pattern of the metabolites in the finished Chardonnays and Cabernets "proves a correlation," Mills said, "but we'll have to do a lot more work to know exactly what happens that distinguishes one wine from another."

Nick Bokulich, who is working on his Ph.D., did the yeoman's work on the analysis, and is listed as the first author. "This is only one of 27 papers he has published," Mills said. "He's a genius." And he's planning on a career in bio-tech and health, not wine research. Connections through his main interests, though, made the machinery available to do the analysis.

What next? "We need to show how these chemical species influence flavor," Mills said.

It won't be easy. "An insane amount of work had to go into analyzing the samples," Mills said, crediting the winery with diligently isolating 700 samples during one harvest crush, "and they had to do each one five times over." That may explain why no one has attempted this work before.

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