Soil science in wine country: probing the mystery of terroir

Posted August 14th, 2008 at 12:57 pm.

For centuries wine makers have understood the importance of terroir—or the combination of soil, climate, and geography that gives the grapes of particular regions their distinct qualities—in making great wine.

But there remains to this day a great deal of controversy as to just what terroir really means and what environmental factors make the difference between a $5 bottle of wine and a bottle to be savored at a special occasion.

Terroir has always had this sort of mystical quality.” says Assistant Professor of Geology Chris Oze. “But now, thanks to geographic information system (GIS) technology, we can look at all these environmental variables—soil chemistry, overall climate, rainfall, how water percolates through the soil, the slope and aspect of how much sunlight the grapes receive within a day—and tackle this idea of terroir systematically and scientifically.”

For the last two summers, Oze and several Bryn Mawr students have been studying the terroir of two Washington State American Viticultural Areas (AVAs) known for producing some of the best red wines the United States has to offer.

In 2007 Oze and students from the Keck Geology Consortium, including Anna Mazzariello ’08, studied the Walla Walla Valley AVA for four weeks. This year, Oze, Nithya Vasudevan ’10, and Paige Walker ’09 studied the Red Mountain AVA.

Oze, Vasudevan, and Walker spent only about a week at Red Mountain this summer but worked from 8 a.m. until the sun went down.

“It was collect data, collect data, collect data, eat a sandwich for 15 minutes. We managed to get the same amount of work done this summer as last but in about a quarter of the time,” says Oze.

“Probably the most exciting aspect of the trip was the time spent in the field doing ‘real world’ geology—we study all these concepts in class and see them in pictures. When we go out into the field, it’s breathtaking,” says Walker.

While at Red Mountain, Oze and the students took soil samples in the vineyards, set up sunlight and temperature monitors, conducted tests to examine the physical properties of soil, and spoke with vineyard owners and wine makers.

Comparing the two areas was particularly attractive to Oze and the student researchers because the vineyards in both areas used the same variety of grape—syrah—and have relatively similar climates but markedly different types of soil.

“Obviously the soil needs to have certain basic qualities for these plants to grow. But once you go beyond that, a lot of people disregard the idea that soil chemistry has much to do with how the plants grow or the characteristics of the grapes,” says Oze.

To test whether the soil differences actually translated into differences in the grapes, the researchers took apart the plants and analyzed the roots, stems, and the grapes themselves for trace metals to see if the chemistry was different on one soil versus another.

“It turns out they were very different. So this is really big in the wine industry because a lot of people dismiss the idea that the soil plays any real role in taste. However, we’ve been able to show geochemically and biochemically that there’s something different happening between these grape plants grown on different soils,” says Oze.

Oze will leave it up to other researchers to decide just how important a role soil composition plays in the taste of wine; the goal of his research is to catalog the variables that exist and to give other researchers a method for examining the viability of any given area for sustaining agriculture.

“Where this research is really important is not just looking at wines. We’re doing wines because they’re fun. They have distinct boundaries for where things are grown, and people speak very highly of terroir, and it’s an interesting idea for us to test scientifically. But what we’re trying to do overall is to create the methodology for the geospacial analysis of these very complex multivariable systems at work in agriculture.

“Hopefully, when we’re done, other researchers can take this methodology and look at areas being affected by climate change, for instance, and see whether existing crops are in danger or if another type of crop might eventually be more viable there,” says Oze.

Vasudevan and Walker agree that this research and the intense fieldwork associated with it has been an experience like no other in their academic lives.

“The entire experience was so much more than I could have ever imagined,” says Walker. “It was inspiring and challenging, it was exhausting and fun. It was an unforgettable, multifaceted experience that will stick with me for years to come.”

“This trip was a fantastic experience. It was my first time on the West Coast, and while we spent most of our time out in rural Washington, we were able to see a lot of Seattle as well. I learned so much about the geology of the state, and loved being out in the field,” says Vasudevan, who has decided to major in geology after also considering anthropology and sociology.

“I was nervous going into a subject that I didn’t really know anything about. Through our department trips and field-work experiences like these, you really begin to understand challenging concepts that cannot necessarily be taught through textbooks and lectures,” Vasudevan added.

In addition to their time at Red Mountain and in Seattle, Oze and the students got to explore the Cascade Mountains, a petrified gingko forest along the Columbia River, and much of the Olympic peninsula.

They even had a run-in with a den of rattlesnakes.

“I was pretty scared at the time but now I feel like Indiana Jones,” says Walker.

Plans are in the works for Oze to take students to Red Mountain again next summer, and he’s hoping that some of their current research will be submitted for publication some time in 2009.

“Birth of a Vineyard,” a short documentary that features Oze (he appears about four minutes into the approximately eight-minute video) :

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