Perfect pairing

From vine to glass, our science has elevated how grapes are grown—and enjoyed.

periodiCALS, Vol. 7, Issue 2, 2017

Chardonnay grapes.

Such a delicate fruit, the grape. Thin-skinned and weighing only a few grams, this tiny berry has become an elemental part of human civilization. First domesticated some 8,000 years ago in mountainous regions of the Near East, grapes—and the culture surrounding them—have spread across the world: fermented for Egyptian pharaohs, celebrated by Greek poets, tended in French vineyards, raised in Chilean high mountains, and nestled along valley hillsides of the Finger Lakes in New York.

Grapes have held an exalted cultural status for millennia. And throughout that time, the fruits have had to be harvested carefully by hand. It wasn’t until 1957 that E. Stanley Shepardson, an agricultural engineering researcher at Cornell, introduced a new method: a harvester that used high-frequency, low-amplitude “bumping” to shake individual grapes off the vines. Grapes used to make wine and juice could be harvested by machine without damaging the fragile fruit.   

“Between the late 1960s and mid-1970s, we went from 100 percent hand picking to 100 percent mechanical picking of juice grapes,” says Cornell senior research associate Terry Bates. “This was a huge advancement. The discovery revolutionized the industry.”

A student on an ATV in a vineyard.
Ground-based sensors like the one mounted to the back of an all-terrain vehicle driven by Anna Long ’15 can provide high-resolution scans of vineyard attributes. Photo by Terry Bates.

At Cornell CALS, our impact on grapes neither starts nor ends at harvesting. For decades, our researchers have been transforming how grapes are bred and grown as well as how wine is crafted. From nurturing promising new grape hybrids to shaping the aroma of the wine that fills a glass, our scientists have affected nearly every piece of the grape growing and winemaking process.

As a result, the New York grape and wine industries have flourished. The state is the largest producer of grapes in the eastern U.S. and the third-largest in the country—boasting over 400 wineries spread across 59 out of 62 counties. More than 100 are located in the Finger Lakes alone, a region dotted with nearly 10,000 acres of vineyards producing some of the finest Riesling found anywhere in the world.

“Without Cornell CALS, there would not have been the long and sustained expansion of the grape and wine industries in the state,” says Sam Filler, executive director of the New York Wine and Grape Foundation. “Cornell has been at the forefront of innovative research for decades, and continues to tackle the challenges we face today and will encounter in the future.”

Computer generated data layers
High-resolution scan of soils, vines and other attributes. Photo provided.

Like the harvester developed in the 1950s, our creative solutions to today’s problems are still helping industries thrive. Drones hovering over vineyards are measuring vine growth and health, allowing managers to spot problem areas early. One day, robots may deftly maneuver through vineyards on their own. Justine Vanden Heuvel, associate professor in the Horticulture Section of the School of Integrative Plant Science (SIPS), is collaborating with Cornell engineers on autonomous robots that can touch, sense and handle grapes. These could soon be collecting real-time environmental conditions and cluster data, streamlining decisions about optimal growing conditions, pest control and harvest.

Grapes and wine have earned a prized significance that shows no signs of diminishing. Our scientists are continuing to address the unique challenges and issues of our time—from managing pests and disease in a changing climate to exploring the science of taste in a world of rapid technological advancement.

Improving Efficiency

Professor holding a drone in a vineyard
Drones collect detailed measurements of growing operations. Justine Vanden Heuvel, associate professor of viticulture, is providing New York growers with the tools to understand and make use of the rich data. Photo by Chris Kitchen.

When it comes to grape vines, there really can be too much of a good thing. That was the discovery of professor of viticulture Nelson Shaulis, who in the 1950s found that thick, lush leaf canopies prevented fruit from getting enough sunlight and drastically reduced grape yields. In 1960, he hit on an idea that became known as the Geneva Double Curtain trellis system. Revolutionary for its time, it involves dividing the vine into two separate, thinner canopies with the help of large crossarms (imagine a single, long row of grapevine trunks with branches outstretched onto two parallel fruiting wires). That configuration exposes more of the fruit to sunlight, which increases grape yields by up to 90 percent. The design proved to be an immediate sensation, especially for the production of juice grapes. It inspired designs for other divided canopy systems as well, and has transformed how grapes of all kinds are grown across the world. 

Squeezing every ounce of productivity from the land is essential for vineyard owners. In the 1970s, they could expect to earn about $220 per ton of Concord grapes, and during the past few decades that number has barely budged. To stay competitive, growers are getting practical help from the Efficient Vineyard Project, a multi-institution effort led by Bates, who also heads the Cornell Lake Erie Research and Extension Laboratory.

A Cornell CALS research vineyard overlooking Cayuga Lake. Photo by Chris Kitchen.

Among other initiatives, Bates is putting sensors to work collecting data on soil, canopy and grape yields. While managers dream of growing perfectly uniform grapes, quality varies across a vineyard. Data from the sensors produce spatial maps to facilitate differential harvesting, making it easier for growers to separate the fruit for wines at different price points, optimizing the usage of every grape. The information can also be used to adapt their fertilizing and pruning to grow more uniform grapes, sustainably, across an entire vineyard. 

 “For growers, the rich data stream allows them to make critical economic decisions that can be the difference between profit and loss,” Bates says.  

Producing grapes is a labor-intensive undertaking. Every season, up to seven or eight times before harvest, growers must sample areas of their vineyard—an expensive effort that entails collecting fruit and studying it for everything from sugar levels and acids to color and aroma.

Using images collected by satellites and drones, Vanden Heuvel is developing processes that may upend that labor-intensive practice without sacrificing quality. Aerial imagery and remote sensing pinpoint representative areas for sampling. One study revealed that using these images cut sampling time by 57 percent. 

“The views from overhead can help growers see where vines are more or less vigorous, which can be an indicator of vine size and health. Both affect fruit composition and quality, and seeing all of these things in a high-resolution snapshot helps growers understand the variability in the vineyard,” says Vanden Heuvel.

Stomping Out Pests and Pestilence 

A grape berry moth
The grape berry moth causes berries to ripen prematurely, split open and shrivel. Photo by Tim Martinson.

One of the most destructive fruit pests in the vineyard, the tiny grape berry moth gobbles up blossoms and small grapes before they ripen. Females lay dozens of eggs on grape stems and berries. As the pupae emerge, they tunnel into the fruit to feast on the pulp and seeds. In 1971, Cornell researcher Wendell Roelofs teamed up with postdoctoral student Jim Tette and Fredonia-based entomology professor E. Frederick Taschenberg to fight this vineyard scourge. In their lab, the trio removed the glands of female moths and isolated Z9-dodecenyl acetate as the chemical that attracts males. They discovered that by synthesizing the compound and releasing it in vineyards it could be used as a potent tool for population control.

“At first, we used the pheromone in traps primarily for monitoring,” Roelofs says. “The capture of males in the traps helped us understand the density of the moths, and when insects were present in the vineyard so that we could time insecticide sprays.” 

Over time, they used the pheromone to disrupt mating entirely. “When we released small amounts of the pheromone throughout the vineyard, it confused the males so much that they didn’t mate,” he says. “We could control them without using insecticide.” In 1990, the researchers released a commercial lure that has proven successful in Israel and throughout Europe in hillside vineyards that tractors cannot easily access.

Vines infected with leafroll
Our researchers are working to thwart destructive diseases like leafroll. Photo by Chris Kitchen.

Today Greg Loeb, professor in the Department of Entomology, is continuing the battle against the grape berry moth by working to develop attractants for females. By understanding the chemical compounds—known as host cues—that the insect uses to determine if a vine will make a suitable home, Loeb is developing improved monitoring tools, which could be applied to create more effective attract-and-kill stations. Eventually the right research could help growers sidestep moth-related problems entirely. 

“Down the road, we may be able to make changes to cultivated grapes that make them less attractive to female grape berry moths as egg-laying sites,” he says.

Our researchers are also working to fight destructive vineyard diseases. In 2005 and 2006, Long Island grape growers turned to Marc Fuchs, an associate professor in the Plant Pathology and Plant-Microbe Biology Section of SIPS, for help with a mysterious condition that was devastating their crops. The unknown culprit was creating poor fruit quality and maturity, and substantially reduced yields. Fuchs suspected a variation of a disease known as leafroll, but by probing the genetic makeup of the virus, he and colleagues, including associate professor Keith Perry, discovered that the troublesome affliction was something never seen before: Red Blotch. 

The virus attacks rootstocks and leaves, and can drastically reduce the sugar content of berries. It proved to be an urgent issue for growers. Fuchs and Miguel Gómez, an economist at the Charles H. Dyson School of Applied Economics and Management, found that infected Long Island vineyards stood to lose more than $8,000 per acre. With more than 2,000 acres of vineyards in the region, the economic loss threatened to reach $16 million or more. 

With further study, Fuchs and his colleagues identified the infection during its earliest stages, and they are now collaborating with the New York grape industry and the New York State Department of Agriculture and Markets to reinstate a certification program to ensure that new planting material is virus-free. 

“The first New York certified vines will be put on the market in 2018, which is fast, considering how long it takes grapes to grow,” Fuchs says. “When growers are dealing with an issue of this magnitude, we go full throttle.” 

Accounting for Taste

Wine aromas and flavors are so varied, they’ve earned a vernacular all their own: a wine can be oaky, buttery, briary, grassy or jammy, with hints of chocolate, clove, cranberry and more. It can be brawny or elegant, harmonious, complex, robust.  

Simply stated, wine flavor is anything but simple. Many factors contribute to each wine’s specific taste and aroma, including climate, horticulture, fermentation and the yeast cultures that transform grape sugars into alcohol.

“We’re at the very tip of the iceberg in terms of understanding what makes wine taste good,” says food science professor Terry Acree, an expert in aroma and our sensory perception of food.

What is known, however, is that balancing several major factors can account for a large part of good taste: tannins, acidity and aroma compounds.

Consumers of red wine are often looking for a good mouthfeel. That pleasantly “grippy” feeling of a full-bodied glass of red results from an optimal level of tannins—compounds that bind to proteins, including the lubricating proteins in our mouths, to create the experience that is critical to the sensory quality of red wine. Too much tannin results in a harsh, drying mouthfeel, and too little creates a thin wine with poor body.

The same principle holds true for aroma compounds. In small amounts, for example, the tongue-twisting chemical tetramethylethylenediamine (TDN) gives Riesling wine its characteristic rubbery odor. But nudge those TDN levels up and the wine starts to smell like petrol. 

Acree’s findings on aromas are the result of a lifetime of research that started with an unexpected connection with Roelofs. In 1970, Acree learned that Roelofs and chemist Heinrich Arn were using insects’ antennae and a technique known as gas chromatography to understand more about how—and what—insects can smell. That inspiration led Acree to develop a similar device that precisely identified odorants in foods.

“We once believed there might be millions and millions of chemicals that cause aroma,” he says, “but there are far fewer. It’s much more accessible than we believed.”

Yet even a smaller-than-expected constellation of aroma compounds still creates a universe of potential sensory perception. The brain integrates three systems—taste, smell and touch—to create the impression of flavor. As no two brains are identical, so too perception varies from person to person.

“In addition to all the things going on in the mouth, wine drinkers are also affected by variation in wine color, label design and even the words used to describe the wine,” says Anna Katharine Mansfield, associate professor of enology in the Department of Food Science, whose research straddles wine production, flavor chemistry and sensory perception.

Flavor variation has implications for winemakers in surprising ways. Mansfield and Gómez discovered in 2014 that sales dipped when wineries provided written sensory descriptions for consumers. The reason: individuals were led to anticipate flavors they might not ultimately detect, resulting in unmet expectations. The discovery prompted redesigns in tasting room literature in wineries across the country.

“Understanding wine components that produce flavor is only half the story,” says Mansfield. “It’s just as important to know how different consumers perceive and interact with wine.”

A student analyzes wine
Enologists perform detailed measurements of wine to assess composition and quality. Danielle Noce, an MPS student in enology, pipets a wine sample in the teaching winery in Stocking Hall. Photo by Matt Hayes.

Gavin Sacks, associate professor in the Department of Food Science, is helping not only to identify aromas and flavors, but to manipulate their expression in wine. Wild grapes native to the Eastern and Midwestern U.S. evolved in that particular climate, accumulating the beneficial genetics to survive without being sprayed against pests or shielded from harsh winters. The downside, however, is their poor flavor. Their acid concentration, for example, is closer to a cranberry or lemon. 

Sacks is working with grape breeders to identify the genes that control traits responsible for undesirable flavor characteristics. As part of a USDA-funded project, he is speeding the process of measuring key aroma compounds in the tissue of grapes and other plants that are often present at trace concentrations (in parts-per-million or lower), making accurate measurements challenging and time-consuming. 

“Current methods for quantifying key odorants take 30 to 60 minutes per sample,” Sacks says. “That sounds fast until you realize that a grape breeder might have 20,000 grape crosses they would love to analyze.” The Sacks group is developing microfabricated films to rapidly extract and then analyze volatiles in plant samples, with a goal of decreasing analysis time to 30 seconds per sample or less.

While Sacks is quick to point out that winemaking isn’t an exact science—“there’s still a significant degree of artistry,” he notes—scientists’ increasingly robust understanding of aromas and flavors is helping vintners develop wines that more perfectly fit their desires, and grape breeders identify early the genes for preferred sensory traits.

Bearing Fruit

To develop a new grape and introduce it to the world requires a supply of patience: from start to finish, the process takes up to 30 years. It starts with scientists envisioning an ideal new fruit—a seedless table grape or an aromatic wine grape with specific qualities, for example. Then, researchers develop “crosses”—offspring of two varieties from the same species—that they think might produce such properties. Each year starting in late winter, Cornell grape breeder Bruce Reisch plants up to 6,000 seeds in a greenhouse at the New York State Agricultural Experiment Station in Geneva. While many seedlings don’t make it through a season, some begin bearing fruit within three to five years. The most successful vines get propagated to make sure the characteristics persist over time. Finally, grapes are tested at different locations to ensure they will do well under varying conditions.

“The ‘eureka’ moments are rare since it can take up to 20,000 seedlings before a single new variety can be identified and released, but those moments feel wonderful,” says Reisch, professor in the Horticulture Section of SIPS.

A professor examines grape leaves.
Bruce Reisch, professor of grapevine breeding and genetics, collects grapevine leaves for DNA extraction in a research vineyard at the New York State Agricultural Experiment Station in Geneva, New York. Photo provided.

New technology has helped scientists hone in on the most promising varieties quickly. VitisGen2, a USDA-funded project co-led by Reisch, is helping Cornell reap the benefits of new tools in genomics.

 “We can test DNA from a small piece of leaf tissue and make sure certain important genes, like those for powdery mildew resistance, are in those seedlings,” he says. “We toss out more than 80 percent of seedlings before they are planted in a permanent vineyard, and that allows us to be much more efficient with our resources.” 

One of the breeding program’s biggest success stories has been Cayuga White, a hybrid wine grape released in 1972. Before that, regional growers often favored Seyval blanc—a hardy white wine grape well adapted for the Finger Lakes. But when Cornell researchers crossed Seyval blanc with another grape called Schuyler, the resulting hybrid proved even more advantageous. It pairs the benefits of the Seyval blanc with high productivity and remarkable adaptability, says Cornell extension associate Hans Walter-Peterson, viticulturist and team leader for the Finger Lakes Grape Program

“[Cayuga White] can be made into sparkling wine, still wine and blends. That versatility means there’s a lot of demand for it,” Walter-Peterson says. “It has shown how successful a hybrid release can be and how much impact it can have on an industry.” And it’s something wineries have noticed. Bully Hill Vineyards, a winery on Keuka Lake in the Finger Lakes, for example, has pledged to support hybrid grape research for the next five years.

A student examines grapes
Doctoral candidate Anne Kearney examines Chardonnay grapes. Photo by Chris Kitchen.

Cayuga White has earned its own modest place in the history of wine, enjoying high popularity in the Northeast and, as of 2017, accounting for more than $20 million in annual wine production in New York. Cayuga White illustrates the success that has resulted from our dedication to the fragile and humble, but much celebrated, grape. 

And the work continues, says Walter-Peterson. “We’re always asking: how can we use the new tools we have today to do it again?”