The gradual rise in global temperatures over the past few decades has been leaving its mark on wine. So far, the news has been good—wine quality for recent vintages is better than it was 50 years ago, according to connoisseurs. Furthermore, the warming climate has enabled vineyards to thrive in areas where the weather was previously too cool or too variable for growing high-quality grapes. Despite these short-term benefits for both winemakers and connoisseurs, the rise in global temperatures expected for the next half century may ultimately bode ill for the wine industry. Although some growers may find different grape varieties that are suitable to the new climate regime, environmental conditions in some famous grape-growing regions may turn too hot or too dry to support vineyards.
Meanwhile, vineyard personnel are beginning to develop new techniques for producing consistently better fruit. These technologies, such as tailoring vine care on a row-by-row and even plant-by-plant basis, may prove of value in adapting vineyards to climate change.
Geography in a bottle
Archaeological evidence, as well as genetic analyses of various grape species, suggests that wine making originated in the Caucasus region of central Asia about 5,000 years ago, says Artimus Keiffer, a geographer at Wittenberg University in Springfield, Ohio.
The first batch of wine probably stemmed from an accident. Airborne yeast spores may have drifted into a container of grape juice and then fermented the sugars in the liquid, producing alcohol. Ancient vintners then built on nature’s work, gradually devising techniques that yielded higher alcohol content. Early wine, notes Keiffer, “probably was pretty rotgut stuff.” Romans refined the wine making process around 2 millennia ago. As a rule, however, wines weren’t bottled for later consumption until the 1800s, says Keiffer.
Because grapes come in many varieties, each with its own portfolio of chemicals producing flavor and aroma, wine has no distinct formula. Today’s diversity—from Bordeaux to merlot, from champagne to chardonnay—reflects the complex interactions between a region’s soil, topography, climate, grape varieties, agricultural practices, and wine-making techniques, all of which can inextricably link particular wines to particular places. Little wonder, then, that wine sometimes is referred to as “liquid geography.”
The distinctive qualities associated with wine from a particular grape-growing region often are collectively termed terroir, a French word that in its narrowest sense means “soil”. Connoisseurs rabidly debate which factors are the most important contributors to wine’s character (SN: 1/1/00, p. 12: The World of Wine). “Terroir is the lightning rod of the geography of wine,” says Percy H. Dougherty, a geographer at Kutztown (Pa.) University.
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A wine’s characteristic tastes and aromas are attributable to small amounts of many different chemicals. Those substances can number in the thousands, but wine judges typically classify each wine into 1 of 12 general categories such as “fruity,” “nutty,” or “earthy”. Among the many more-descriptive words that connoisseurs use to describe a wine are such positive characteristics such as strawberry jam, bell pepper, and fresh-cut grass. Negative descriptors include burnt toast, moldy cork, wet dog, and wet cardboard.
Each mix of flavors depends in part on flavor chemicals that aren’t present in the grapes when they’re harvested but form during the fermentation process. Other flavoring molecules can leach into the wine from the wooden barrels often used during the aging process. Even the dust in the air when the wine is being bottled can make a difference in flavor.
Many of the flavors, however, result from the beverage’s primary ingredient. “All wine starts out as grape juice,” says Keiffer.
Major components of grape juice include the sugars, acids, and other chemicals, such as tannins and flavonoids that are produced as the fruit ripens. The proportions of these various substances greatly depends on weather at the vineyard during the growing season, says Gregory V. Jones, a climatologist at Southern Oregon University in Ashland. As the grapes mature, the concentrations of sugars in the fruit increase while those of acidic compounds drop. However, many of the trace chemicals that impart flavor to a grape’s juice develop independently of the acids and sugars, and they often show up late in the fruit’s maturation.
When weather is warmer than the optimum for a particular grape variety, the fruit ripens and achieves the best balance of acids and sugars long before the rest of the wine’s flavorful substances show up in the proper amounts, says Jones.
Different species of grapes grow best in different environmental conditions, but the climate in most grape-growing regions today generally matches the conditions in central Asia when wine making first developed: temperate, with plenty of rain. Average annual temperatures in the world’s premier grape-growing areas are between 10°C and 20°C, says Dougherty.
Dissemination of the wine making craft typically occurred by transplanting grapes from areas where vineyards were successful to locales with a similar climate. In most wine-producing areas of Europe, generations of vineyard owners have had hundreds of years to identify the optimum grape for their site. In Oregon, where wine making is a relatively new industry, most grape growers still are searching for the varieties that will do best, notes Jones.
To help the state’s entrepreneurs make up for lost centuries of wine-making experience, Jones and his colleagues have developed a model that can assess a particular plot’s promise as a vineyard and help farmers select their dream grape.
Although the predictive scheme is “still very much a work in progress,” says Jones, as many as a dozen Oregon growers have chosen a grape variety for their new vineyards on the basis of the model. A handful of growers with established vineyards have changed from one grape varietal to another according to the model’s recommendation.
One part of the researchers’ model uses computerized topographical maps. In Oregon’s Umpqua Valley, for example, the best sites for vineyards are between 120 meters and 240 m in elevation on hillsides with a slope between 5° and 15° that face a southerly direction. These areas provide the best exposure to sunlight, and the gently sloping hills permit cold air to flow away from vines, thereby protecting them from mild freezes.
The computer model also assesses a site’s soil on the basis of its drainage, pH, water-holding capacity, and thickness. Important climate variables include the coldest temperature that the site experiences in winter, the interval between the last frost of spring and the first frost of the autumn, the temperatures typically experienced during that growing season, and the frequency and amount of rainfall when the grape vines flower and when fruit is harvested.
The sum of the topographic, soil, and climatic scores assigned to a site by the model provides a composite rating that can guide growers regarding the grape varieties that may be well suited for their vineyard. Pinot noir grapes grow better in cooler areas of the Umpqua Valley, while the tempranillo and syrah varietals are better suited for warmer zones. “Picking a site and a [grape] variety is half the battle,” says Jones.
The other half of the battle has a global, rather than a local, dimension.
Climate change is complicating vintners’ choices today and probably will do so for years to come. Jones and his colleagues have studied the effect of the recent rise in average global temperatures on the quality of wines from 27 wine-making regions.
Between 1950 and 1999, the average annual global temperature has risen about 1.26°C, says Jones. During that period, vintage ratings—the assessments of wine quality compiled each year by judges of Sotheby’s auction house—improved for all 27 of the wine-making regions. Although some of these gains may be the result of better wine-making practices, many may result from warmer temperatures.
In traditionally cool regions, the increased temperatures wrought by global warming have provided better ripening conditions and more consistency from one year to the next. For instance, in the Rhine and Mosel areas of Germany, two grape-growing regions with cool climates, grape quality has improved in recent years. In Oregon, winemakers have had good vintages for 8 consecutive years, whereas experience suggests they’d garner only 2 good years out of 10.
Consistently warmer temperatures during the growing season have recently enabled vineyards to thrive in southern England. That region was home to many vineyards in the 1600s and early 1700s, a time before a drop in global temperatures known as the Little Ice Age wiped out the wine-making industry there. Global temperatures still are rebounding from that 2-century lull, says Jones.
Although the recent rise in global temperatures has improved wine quality, the 2°C jump expected to occur by 2050 might not prove to be beneficial everywhere. While vineyards in some cool grape-producing regions may continue to see grape quality rise, vineyards in currently warm climates might be challenged by increased drought, fruit that ripens before its flavors fully develop, and larger or more-frequent infestations of disease or agricultural pests. Grape growers in those locales may minimize their losses by planting different grape varieties or using different agricultural practices.
As winemakers anticipate the need to adapt to changing climate conditions over which they have no control, they’re turning to new agricultural techniques to wield more control wherever they can.
Broad efforts to use technology to improve grape-growing techniques—a farming philosophy known as precision viticulture—are ongoing in many places, including Australia.
In precision viticulture, grape growers tailor their agricultural practices to different parts of the vineyard. First, the farmers create detailed maps of their vineyard that depict critical parameters such as the quality, depth, clay content, water content, and pH of soil, as well as the amounts of water, fertilizers, pesticides, and other chemicals that were used in various sectors of the site. Then, the growers assess the yield and quality of grapes that they harvest, using measures such as the number of grape bunches per vine, the weight of each bunch, leaf area per vine, the pH of a grape’s juice, and the concentrations of various flavor chemicals in the grape.
After analyzing this wealth of data, the farmers adjust their practices during the next growing season, collect more data on quality and yield, and continue the cycle.
Australian assessments of precision viticulture have been under way for 5 years. In agricultural terms, the technique is still in its infancy, but results are tantalizing.
Some studies have shown that annual grape yields per acre within the same vineyard can vary by a factor of 10. For a particular site, that variation typically holds, regardless of year-to-year changes in the weather, reports Rob Bramley of the Cooperative Research Center for Viticulture in Glen Osmond, Australia.
Variation in yield can dramatically affect a vineyard’s bottom line. Data gathered at an 18-acre vineyard in the province of South Australia suggest that if grape growers were to provide the same amounts of water, fertilizer, and other chemicals to the entire vineyard—and use consistent agricultural practices throughout the plot—up to one-third of the vineyard’s area would operate at a loss. The studies also confirm that variations in the wine quality can be large within a single vineyard. Quantifying those differences, perhaps even before harvest, could be useful for a vintner’s decision of what grapes to use in pure wines and in blends, says Bramley.
Currently, farmers sample their vineyards in many places to provide information for the maps, but less costly and invasive techniques are on the horizon. For example, aerial photos taken in a number of wavelengths of light provide information about overall vine health and fruit quality.
One of the keys to growing grapes is maintaining the optimum soil moisture, a parameter that varies according to the grape variety being cultivated. If there’s too much moisture, the vines grow too many leaves, grapes don’t ripen on time, and fruit quality suffers. If there’s too little moisture, the crop withers on the vine.
In traditional methods of monitoring the soil’s water content, growers drill sample holes throughout the vineyard—a time-consuming process that often isn’t sufficient because soil properties can change dramatically in the span of just a few meters. Now, Susan Hubbard of the Lawrence Berkeley (Calif.) National Laboratory, and her colleagues are developing a way to use ground-penetrating radar to quickly and easily measure soil moisture.
The researchers have built a vacuum cleaner-size device that beams radar waves into the ground. Rather than analyzing the waves that bounce off buried objects or other irregularities in the soil, the researchers measure the speed at which the waves travel through the ground. The waves travel more slowly in wet soil, says Hubbard.
In field tests in California’s Napa Valley, Hubbard and her colleagues have towed the device through the vineyards to produce detailed maps of soil moisture. That information would enable grape growers to refine their irrigation schemes on a row-by-row, or even a plant-by-plant, basis. Then, vines could receive optimal moisture throughout the growing season.
Potential benefits of precision viticulture include more cost-effective and environmentally friendly irrigation and fertilization regimens as well as increased quality and yield, says Bramley. Monitoring conditions throughout the growing season enables grape growers to schedule their pruning of vines and the harvest to maximize grape quality.
For example, growers can collect data to relate specific vineyard conditions to grape quality. Premium grapes sometimes sell for almost four times the price of nonpremium fruit, says Bramley. When growers who used precision viticulture at one 8-acre vineyard in western Australia sold their best grapes separately from the rest, they boosted the retail value of the wine more than $70,000.
Technological tinkering probably won’t make great wine vintages any better, says Hubbard, but it could significantly improve what otherwise might have been an average year of wine making. With more consistent grape quality, year-to-year variations among vintages might decrease as well.
On the other hand, such technology might have unintended consequences, says Jones. Wines whose qualities are consistent over time may lack the full range or interesting balance of flavors that might be produced serendipitously at a neighboring vineyard that is managed less scientifically.
Say Jones: “Some wine connoisseurs cherish the differences between vintages, rather than their similarities.”
However, increased reliance on techniques such as precision viticulture could become a vintners’ primary method of counteracting the worldwide warming that’s expected in the coming decades. As a consequence, the nuanced flavors of one of mankind’s favorite beverages may be increasingly hard to come by.