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Oregon Wine

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OSU researchers help bring the full flavor of grapes to Oregon wines.
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OSU viticulture extension specialist Patty Skinkis discusses how OSU is helping the Oregon wine industry.

On a hillside vineyard in Yamhill County, the sun gently coaxes grapevines out of their winter hibernation. Tender green shoots, tempted by the warmth, emerge from the trellised arms of the craggy, weathered vines. From these shoots, clusters of tiny flowers reach toward the sky. As the days warm, the flowers will swell into fruity, purple Pinot noir pearls.

This is how wine begins, in the soil and sunshine of southern Oregon, along the Columbia River, or here in the Willamette Valley. The process of making wine is complex, and scientists at Oregon State University are refining the process to help the state’s vineyards and wineries stay competitive. Each researcher brings something to the table as an expert in viticulture, enology, or flavor chemistry. Combine them, and you’ve got a robust, delightfully lively assemblage of researchers—from vine to wine.

We begin in this postcard-perfect vineyard, where Patty Skinkis points out something unusual among the vines. Some have more foliage, longer shoots, and deeper green leaves. The reason, she explains, lies at our feet, in the alleyways between the vines where some rows are bare soil and others are carpeted with grass.

wine grapes by Lynn Ketchum

Skinkis is a vine expert at OSU, and she’s been studying these vineyard alleyways at Stoller Vineyards for the past three years to see how they impact the growth of vines and the quality of the grapes. Her study suggests that using a cover crop in alleyways year-round in a mature vineyard produces higher-quality grapes and a better bottom line.

To understand why, it helps to know a little about vineyard management practices in the north Willamette Valley. Vineyard managers in the area often plant cover crops, like grass, to keep soil from eroding during the rainy winter and to provide traction for machinery. But this costs money. When spring rolls around, some managers plow up the grass so that it doesn’t compete with the vines for water during the drier summer. This, too, costs money. Managers also often fork out cash to prune back leafy canopies, which grow rampantly during the Valley’s wet spring.

It seems that the Valley’s fertile soil and abundant spring rain may encourage too much growth from the grapevines. Overzealous canopies increase the possibility of diseases and make it harder for the sun and air to reach the fruit. But Skinkis has found that vines that are sandwiched between grass-covered rows don’t grow as vigorously as those that are next to bare rows. That’s because the grass steals some of their nutrients, but it doesn’t compete with the vines for water.

red wine by istock

Better yet, Skinkis has found that grapes from these same vines with grass alleyways scored the highest in terms of phenolics, which affect how wine feels in the mouth, and anthocyanins, which are pigments that produce a more intense red—a desirable trait in Pinot noir and many other red wines. That increased quality could translate into higher prices for Oregon grapes and for the wine made from them.

As we follow those good grapes on their way to becoming great wine, we next encounter the fun guy of fungi, the party animal of the food world: yeast. On first glimpse under a microscope, these ubiquitous, one-celled creatures appear to be rather simple white dots. But as OSU microbiologist James Osborne demonstrates, when you drop them into a vat of grape juice, it becomes an unsupervised swim party. They’re soon working up a sweat, blowing bubbles, recklessly reproducing and practically wearing lampshades on their heads.

Having an insatiable sweet tooth, yeast will binge on sugar in the grapes like kids tearing into candy bars. Along the way, they convert the sugar into carbon dioxide and alcohol, but this very alcohol will eventually get so strong that it kills them. With that, their gluttonous corpses sink to the bottom of the vat into a pasty mass. The party is over, someone turn off the lights.

wine bottles by istock

Yes, yeast know how to have a good time, but they deserve it. After all, they’re the tough little workhorses that for thousands of years have been helping make our breads, beers, and, of course, wine. Yeast are vital to wine production because besides the grapes, they’re the only other ingredient needed. Grapes naturally have yeast on their skin, so it’s possible to make wine without actually adding any of these little eukaryotic critters—a process known as native fermentation. Most wineries, however, buy yeast to add to the grape juice in what’s called inoculation so they can have more predictable outcomes.

Still, yeast’s role in winemaking isn’t fully understood, particularly in red wine, Osborne says. “There are unanswered questions like what advantage do you get from native fermentation versus inoculation and does it matter what yeast you’re using?”

Osborne is prying into the secret life of yeast to see how they impact the aroma of Pinot noir. His goal is to help winemakers select strains of yeast that can produce the aromas and flavors they desire. So he and graduate student Dave Takush produced a handful of Pinot noir wines that each used a different strain of yeast. They controlled every aspect of the winemaking process so that any observable changes were due only to the yeast. After that, trained sensory panelists assessed the wines.

wine grapes by Lynn Ketchum

Preliminary results show that the testers detected statistically significant differences among the wines made with the different yeasts. For example, panelists described one wine as having enhanced blackberry and dark cherry characteristics. Another had red fruit qualities such as fresh strawberries, raspberries and cherries. A third stood out for its aromatic characteristics of jam.

If funding comes through, Osborne aims to hand the wines over to his colleague Michael Qian (pronounced chen) so that Qian, a flavor chemist, can determine exactly which chemical compounds are giving the wine its aroma.

A wine typically has hundreds to thousands of aroma compounds, Qian says. It’s not actually possible to see them because they’re just elements of the periodic table—often oxygen, hydrogen and carbon—that are bound together. Depending on their combinations, they might form, for example, isoamyl acetate, which smells like bananas, or citral, which has a hint of lemon.

Qian identifies these compounds by using a whiz-bang machine that’s about the size of an oven but costs as much as a house. Making friendly little R2-D2 noises, this sophisticated schnoz sniffs out the compounds from the wine and rollercoasters them through a coil of fine glass tubing. It then graphs compounds on a computer in what looks like a wildly erratic electrocardiogram as the equipment puffs the aromas into the air through a little glass cup. All Qian has to do is press his nose into the cup as if smelling a flower, and there it is, the scent of bananas, pineapple, or perhaps cut grass.

Levi Fredrikson and Patty Skinkis
Levi Fredrikson, a graduate student at Oregon State University, works with OSU viticulturist Patty Skinkis to measure the shoots on grapevines at Stoller Vineyards in Dayton. They are examining how grass in the pathways affects the growth and quality of the grapes. Photo by Tiffany Woods.

Qian has been using this machine to analyze the aroma compounds in the wine made from the grapes involved in Skinkis’ cover crop research at Stoller Vineyards.

It’s an amazing process, really, to be able to track a glass of wine back to the vat and vineyard. Or to say that a strain of yeast created a cherry aroma, or that an alleyway of grass produced a darker Pinot noir. For the most part, Mother Nature decides what goes into that glass: sunshine to warm the grapes; a breeze to cool them; nitrogen in the soil to nourish the vines; rain to quench their thirst. OSU’s researchers know they can’t control Mother Nature. But they’re doing their best to fine-tune other factors within their powers—all in the quest to make the perfect glass of wine.


Web resources

OSU Viticulture and Enology