Science, Tech & Environment

Like the wine? Thank an earth scientist

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Credit: Courtesy of Kevin Pogue
Rocks transported by a glacial event influence the flavor of wine at Red Willow Vineyard in Washington state.

There are few things that geologist Kevin Pogue loves more than gazing into a pit in the ground. Especially in Washington, where he lives.

There’s a lot of “weird stuff” to discover: sedimental remains from a glacial event known as the Missoula Floods, which passed through the area roughly 15,000 years ago; fist-sized gravel, encrusted with white, powdery calcium carbonate; iron-rich, fractured basalt, cooled from lava flows; granite chunks that once cleaved to icebergs; and silt deposits from massive dust storms.  

“When I look into the ground, I might see [the remnants of] multiple catastrophes,” Pogue says.

A typical geologist might use such expertise to monitor natural disasters or assist energy companies in scouting for valuable natural resources. Not Pogue — he uses his rock knowledge to help vintners find prime sites for grape growing.

“If you have a piece of land in mind, Kevin can put you on the right direction and tell you if it’s too cold or if the soil’s too rich for growing high-quality grapes,” says Christophe Baron, owner of Cayuse Vineyards, in Walla Walla, Wash.

Pogue is a leading global expert on “terroir,” a French term that refers to the soil, climate, and other environmental properties that influence how wine grapes mature. (Terroir can also refer to the winemaker’s process and how cultural factors, such as irrigation policy, shape their practices.) While the concept of terroir has been around for centuries, applying science to vineyard siting is a recent and growing area of research.

Pogue is one of a handful of U.S.-based scientists who study terroir, and he’s bent on helping vintners find sites that have something to say.

“You can grow grapes most any place,” he says, “but not all places are capable of creating wines with unique and compelling personalities.”

Middle-aged, with an earnest and nerdy enthusiasm, Pogue certainly seems less pretentious than the stereotypical, snooty wine connoisseur. Before he became interested in terroir, he spent a decade studying a major tectonic event known as the Indo-Asian Collision, first as a graduate student at Oregon State University and then as a professor at Whitman College in Walla Walla, where he still teaches geology. During that time, he spent about a month each year digging up rocks in northern Pakistan. After the Sept. 11 attacks, however, safety concerns forced him to change his focus.

At around the same time, the wine industry in Washington was surging, and new vintners began asking him for advice on where to plant their vineyards.

“Here in Washington, we have an interesting geological history, and [winemakers] wanted to incorporate that into their marketing,” Pogue says.

For instance, some vintners wanted to be able to tell their customers that their grapes were growing in ice age flood deposits, a key feature of the Columbia Valley, a certified American Viticultural Area (AVA) that spans central and southern Washington. An AVA is an area of land with a distinct set of grape-growing conditions, which encompass the region’s soil, climate and elevation features. Several AVAs exist within the Columbia Valley AVA, such as Walla Walla’s, where cabernet sauvignon, merlot and syrah dominate the region’s wine production.

While Pogue was happy to advise local vintners, he hadn’t thought about turning his service into a business until Norm McKibben, a pioneer of the Walla Walla wine industry, invited him to survey a potential vineyard site. McKibben, impressed with Pogue’s knowledge, encouraged him to become a vineyard consultant. Shortly after, Pogue founded his side business, VinTerra Consulting.

“The more information [vintners] have, the better they can do their job,” says Jonathan Swinchatt, a geologist who co-authored The Winemaker's Dance: Exploring Terroir in the Napa Valley. “In my experience, [vintners] learn more than they expected [from geologists].”

A wine’s taste is the product of the winemaker’s process and the terroir. Commercial wines, for example, are often heavily processed and tend to include additives, such as sugar and oak chips, that can cloak the wine’s natural flavor.

“By over-extracting the grapes during winemaking and adding enzymes and colors, a winemaker can do hundreds of things that would overwhelm the flavors, textures, and aromas associated with terroir,” Pogue said. “It’s one of the easiest things to destroy in the world.”

If the winemaker takes a more minimalist approach, however — one that relies less on additives and more on the terroir to influence the wine’s taste — an imbiber can notice the difference. Pogue, who is especially interested in helping vintners craft unusual tasting wine, actively seeks vineyards where grapes might struggle for moisture.

“You get better wine from grapes that aren’t the happiest,” says Pogue. “If you give grapes plenty of water, it will produce big berries with thin skins. The wine ends up tasting watered down. If the grape senses that water is scarce, it will produce smaller berries with thicker skins. A higher skin-to-juice ratio will make a wine with more concentrated flavors.”

That’s because the skin, not the juice, is where much of the wine’s flavor, and color, come from.

Pogue advises vintners to steer clear of choosing fields that are flat, with deep soils and a high water table, where grapes will receive lots of moisture — those conditions can lead to uncontrollable vine growth and a lower skin-to-juice ratio. Instead, he looks for features that will restrict water availability, including slopes and rocky soils — basically, “land that makes driving farm equipment difficult” and that wouldn't accommodate tilling.

The types of rocks in the soil also matter. Much of the Walla Walla Valley is covered in basalt cobblestones, which, due to their dark color, heat up the earth more than grass and other rocks, such as sandstone. Hotter soils can act as a cue that causes grapes to ripen faster, says Pogue.

Other aspects of a region’s terroir and its effect on grapes are less clear, however. For instance, scientists studying terroir don’t know how soil chemistry influences the phenolic compounds in the grape’s skin. An investigation into the relationship would help explain why one wine will taste strongly of ripe berries, while another — made from the same grapes in a different vineyard — will taste like a spice medley. Pogue hopes that geologists and organic chemists will eventually collaborate to figure out the mystery.

Another factor that scientists don’t fully understand is how climate change will influence the growth of wine grapes. Some areas, such as Napa Valley in California, could become too hot to cultivate vineyards, while other areas such as Idaho's Snake River Valley, could eventually end up with ideal grape-growing conditions.

“Will Napa Valley be making wine the same way 50 years from now? Probably not in the exact same way,” says Greg Jones, a climatologist at Southern Oregon University who also studies terroir. “If climates continue to change, people will have to adapt by changing their management practices or moving up in elevation or latitude to plant vineyards.”

As scientists like Pogue continue uncovering the complexities of terroir, one thing seems clear: Wine will keep getting better.

“For thousands of years, people figured out good vineyard sites through trial and error, and it’s only recently that people began to think, let’s use everything we know about soil, geology [and] climate to find the best spot to grow grapes,” Pogue says. “It’s an exciting new application of earth science. We’re only beginning to understand it.”  

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    Credit: Courtesy of Kevin Pogue
    Missoula Flood sediments influence the wine flavors at Terra Blanca Vineyard in Washington.
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    Credit: Courtesy of Kevin Pogue
    Loess-based soils and basalt bedrock influence the flavor of the wine at Spring Valley Vineyard in Washington.
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