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Can Microbes Help Scientists Crack Wine's Terroir Code?

That distinctive Marlborough Sauvignon Blanc flavor may be due to the local yeast
Dry yeast waiting to take a bath in delicious grape juice.
Photo by: PWFolsom/Thinkstock
Dry yeast waiting to take a bath in delicious grape juice.

Augustus Weed
Posted: October 1, 2015

Scientists in New Zealand and the U.K. may be one step closer to understanding the mystery of how terroir shapes a wine. They’ve found that microbes, specifically those tiny winemakers called yeast, play a larger role in a wine’s regional identity than previously understood.

Researchers from the University of Auckland and the University of Lincoln in the U.K. isolated strains of Saccharomyces cerevisiae, the primary species of yeast used to turn grape juice into wine, from six New Zealand regions and discovered that different regional strains produce distinct aromas and flavors.

“Classically the concept of terroir was thought to be driven by some complex mix of the particular climate and soils vines grow in, overlaid by the way the vines are managed,” said Dr. Matthew Goddard, a biological sciences professor at the University of Lincoln and coauthor of the report. “No one really considered the role of microbes.” That changed when research found regional differences in various yeast strains.

For the study, published in Nature’s Scientific Reports, the team isolated yeast populations from six different growing regions in New Zealand, using samples from wineries in Nelson, Martinborough, Hawkes Bay, Central Otago and the Awatere and Wairau Valleys (both in Marlborough). They identified which strains of Saccharomyces cerevisiae were distinct to each area.

To test the yeast’s effect on wine, they sterilized Marlborough Sauvignon Blanc juice, removing any other yeast strains hitching a ride, and fermented it in six lots, using a different strain with each batch. The wines were then analyzed for concentrations of 39 different chemical compounds responsible for producing various flavors and aromas that are derived from the fermentation process.

The tests found that levels of 29 of the compounds varied according to the regional yeast strain. Yeast from Nelson on New Zealand’s South Island had greater concentrations of the chemicals perceived as apples and sweet fruits than Central Otago and Martinborough. The Awatere and Wairau strains, on the other hand, had more of the compounds that create floral, apple and honey aromas and flavors.

The results surprised Goddard, who didn’t expect to find any variations. “I think the classic ideas of climate and soil are the main drivers of terroir, but this shows that microbes have a small but significant effect,” he said, noting that no study has quantified how much of an effect it is.

For winemakers, the findings add one more factor in deciding which yeast should be fermenting their wines. Various cultured strains are already known to produce distinct flavors and styles. Some winemakers argue that ambient yeasts, rather than strains winemakers have selected, produce more distinctive local flavors despite their unpredictability, and the study seems to supports this theory. Others prefer to rely on commercially cultivated strains, which are more efficient and less likely to break down during fermentation.

Yeasts don’t always give winemakers a choice, however. They’re tenacious organisms that exist almost everywhere, lingering in a winery for years or hitching a ride on equipment from one winery to the next.

Michael Brajkovich of Kumeu River has been a believer in ambient yeast for years. (His vines have also been a source of yeast strains for Dr. Goddard.) "We started using wild yeast for red wine in 1984 following my [working harvest] in Bordeaux with Jean-Pierre Moueix. We expanded that to white wines in 1986," he told Wine Spectator. "Yes there is a significant difference in quality. For many other producers this type of rigorous evidence is further encouragement to at least try using wild fermentation."

The authors also suggest that the study could have wide-ranging implications for sustainable grapegrowing and other crops. Maintaining the biodiversity of a patch of land could help sustain the native populations of yeasts, allowing vintners to better define the terroir of their vineyards and regions.

How winemakers respond to the study or decide to use it remains to be seen. “The bottom line is that wine is still the product of terroir,” said Goddard. “We just have to widen our concept of what is included in terroir to the other living things in the region—like the microbes.”

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