James Osborne studies the tiny organisms that perform the everyday miracle of turning water into wine. “You can’t make great wine from bad grapes,” Osborne likes to say. “But you can make some really lousy wine from great grapes.”
Oregon has great grapes—everybody knows that. That’s why Osborne and his colleagues, flavor chemist Michael Qian and sensory expert Elizabeth Tomasino, are probing this universe of tiny things, helping winemakers achieve the full potential of their world-class raw material.
For Osborne, the focus is microbes. For Qian and Tomasino, it’s esters, pyrazines, terpenes, thiols, sulfides, phenols: all the aromatic molecules that make wine smell and taste fruity or flowery or herbaceous or—sometimes—like garlic, wet sheep, or rotten eggs.
“With microbes in wine, there are two sides to the coin,” says Osborne. “The one side is improving wine quality by understanding how different yeasts and bacteria produce different compounds that beneficially affect the wine’s flavor, aroma and mouthfeel.”
The flip side is the “bad guys”: microbes that lurk in the grape skins or juice, or in the finished wine, causing it to smell like nail polish remover or a horse’s stable. “The question is, how can we manage the winemaking process to favor the guys we want to grow, and discourage the guys we don’t want?”
The main good-guy microbes are yeasts, which eat the sugar in the juice and convert it to alcohol. For centuries, winemakers relied on yeast that was naturally present on the grapes or in the winery. Wine fermented in this way was unpredictable in quality—potentiallygreat or terrible or somewhere in between.
Today’s winemakers typically use purified strains of the Saccharomyces yeast genus (the name comes from the Greek for “sugar fungus”) to ferment the juice. The most common Saccharomyces is S. cerevisiae, used to make wine, bread, and beer.
However, some of the naturally-present, non-Saccharomyces yeasts are thought to lend their own subtle flavors and aromas. Supply firms now offer packaged, purified strains of these yeasts. Winemakers can add them back into the must (the fermenting juice) together with an S. cerevisiae strain and take a shot at mimicking a “native” fermentation with a little more control and consistency.
Many of these non-Saccharomyces yeasts, not being great fermenters, are quickly outpaced by Saccharomyces. To slow things down, winemakers often employ a technique known as cold soaking: chilling the processed grapes in tanks for up to 10 days. The colder temperatures restrain Saccharomyces growth while allowing the other, more cold-tolerant yeasts to grow and, presumably, develop their delectable notes.
No one knew for sure whether the non-Saccharomyces yeasts present during a cold soak were actually contributing to the wine’s flavor and aroma. To find out, Osborne and his students performed several Pinot noir fermentations, comparing cold soaking treatments that used various non-Saccharomyces yeasts. They also fermented a control batch that was not cold soaked.
The researchers made wines from all the treatments and tested their aromas and flavors. Somewhat to their surprise, the wines from the cold soak treatments were very different from those fermented without cold soaking. What’s more, says Osborne, “they were all nice wines, with distinctly different aroma compounds.” The findings show that cold soaking is indeed an effective technique for managing the microbes in the early fermentation, helping vintners develop distinctive aromas and flavors in their wines.
Michael Qian has smelled a lot of bad wine in his time. In his lab, he injects a vial of an evil-smelling wine into an instrument called a gas chromatograph-mass spectrometer/olfactometer (a GC-MS for short), which teases the wine apart into its tiniest chemical components.
“Everything happens inside—there’s not much to see while it’s working,” says Qian. “But it will identify about 1,000 chemical components in the wine in about an hour.”
But there’s more. As each compound is scanned, the GC-MS emits a puff of its distinctive odor through a little glass bell, one puff after another. Qian leans over, inhales and frowns thoughtfully. So this is what 4-hydroxy-3-methoxystyrene smells like!
“My job is to study aroma and flavor compounds in foods, including wine,” he says. “In this project, my lab is investigating the off-flavor associated with stressed vines.”
Grapevines that experience stress in the vineyard, he says, can produce juice with undesirable flavor and aroma chemicals. “We don’t know which stresses are responsible for these ‘off’ flavors and aromas,” he says. “It could be related to nutrition imbalance, drought, or nitrogen deficiency, or a combination of many factors. We just know the wines are not good. People describe them with words like ‘tequila,’ ‘gasoline,’ ‘shellfish,’ ‘peanut,’ or ‘ashtray.’”
So Qian is sniffing his way through sample after painstaking sample, trying to figure out which chemicals are producing which odors. Then, with the help of OSU viticulturist Patty Skinkis, he intends to trace the chemical signatures of these smelly wines back to the vineyard and identify the conditions that produced them. Were the grapes grown in a drought year? Were the vines sick, or old, or too young to bear good fruit? Were they poorly nourished? Pruned too heavily or too lightly?
A few years ago, Qian and Skinkis wanted to know whether thinning grape clusters improves the aroma of the finished wine. Winegrowers sometimes clip clusters of grapes off the shoots midway through the season, hoping to concentrate the good chemicals in a smaller crop. Skinkis gave the vines three levels of cluster thinning. Following them through to the finished wine, she and Qian learned, with some surprise, that cluster thinning didn’t boost the good aroma chemicals.
From this and many other such studies, Qian says, winegrowers are closing in on the vineyard practices that produce good wines. “Now we are turning to what makes wine bad,” he says. “And then, hopefully, we’ll find out what we can do in the vineyard to make it better.”
Elizabeth Tomasino studies a big stinker in a small package. The brown marmorated stink bug (BMSB), an invasive pest of many agricultural crops nationwide, is a growing threat in Oregon vineyards, not only because it damages fruit but because bugs caught in the stemmer-crusher can impart a distinctive, cilantro-y odor to the wine.
One of these chemicals is tridecane, contained in a pheromone emitted by the stink bug when it’s under stress (such as being caught in a stemmer-crusher). Unscented by itself, tridecane can mask some of the desirable fruity odors of wine.
The other is trans-2-decenal, which does have a scent. In fact, it has another life as a commercial flavoring ingredient, sold to food manufacturers looking to add “waxy,” “fatty,” “earthy,” “green,” or “mushroom” notes to their products.
At first Tomasino, an enologist and sensory expert, was unsure how serious the stink bug problem really was. After all, Pinot noir is prized for its complex palette of aromas and flavors. Maybe a little bit of “earthy” or “mushroom” would lend a special piquancy to the wine. Teaming with OSU entomologist Nik Wiman, Tomasino made test batches of Pinot noir wine, adding varying numbers of stink bugs to the vats. They analyzed the wine to verify the odor’s key chemical components.
Then she and a student did sensory tests, serving Pinot noir with different concentrations of trans-2-decenal. The evaluators detected the stink bug odor at a fairly low threshold, between 2 and 5 micrograms per liter. If there was much more (between 5 and 12 micrograms per liter), the tasters rejected the wine.
Tomasino did some figuring and determined that more than three bugs per cluster of grapes could produce unacceptably high levels of taint. “While it’s best to make wine free of BMSB,” she says, “this may prove to be difficult in the future due to the increasing prominence of BMSB in vineyards.
”There are ways to reduce stink-bug taint in the winery, she says. One way is to press lightly after fermentation—heavy or prolonged pressing increases concentrations of the tainting chemicals. Another is filtration by reverse osmosis, an expensive strategy that can improve aroma and flavor. A third is adding oak chips to the wine; it didn’t reduce the taint compounds in Tomasino’s trials, but tasters had a harder time detecting the aroma.