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Terroir

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  • 1. GRAPES ARE TERROIR TONG N° 2 –03 – — By Kees van Leeuwen, France —
  • 2. The best expression of terroir is when grapes are fully ripe by the end of the growing season. Overly-vigorous vines don’t produce high- quality red wines. The best conditions for these are met on shallow or stony soils in moderately dry climates, where there is neither too much water or nitrogen. In the case of high-quality white wines, you need regular if not too much water and nitrogen. But in order to have great terroir, the socio-economic conditions must be right too. Terroir is an interactive ecosystem involv- ing climate, soil and vines. There is no ideal climate for fine wines in terms of temperature, rainfall or solar radiation, and there is no ideal soil in terms of depth, or its content in pebbles, clay, lime or minerals, simply because these environmental factors only make sense when they interact with the vine. History, socio-economics and viticultural and oenological techniques are also essential to the understanding of terroir. Socio-economic history may help us understand why a given vineyard has emerged and prospered in a par- ticular site, and mastery of viticultural and oenological practices is indispensable for making the best of the natural environment. The human factor It goes without saying there would be no vine- yards without human intervention. Vines, like olive trees, don’t need much water or minerals, so farmers have traditionally reserved their richer soils for cereals and grazing, planting their vines on shallow or stony soils, or on steep slopes. None of the currently cultivated varieties of Vitis vinifera were ever to be found growing in the wild – grapevine varieties were developed to produce high-quality wines. Vineyards have always developed where the socio-economic conditions were favourable – close to towns and their potential consumers, near harbours or navigable rivers. Where the natural environment was conducive to growing quality wines, the vineyards survived; else- where, they did not. Vineyards naturally developed outside Paris – always a centre for wine consumption. In 1820, the region was producing up to 4.8 million hectolitres of wine on 24,000 ha, although climatic conditions were far from ideal. With the opening of the Paris-Lyon- Marseille railway in the second half of the 19th century, when transport was no longer –04 – TONG N° 2 We viticulturists care deeply about terroir because it’s what connects a wine’s taste and smell to where the grapes were grown. Terroir goes a long way to explaining differences in the quality and styles of wines, and yet it is tricky to approach scientifically because so many interacting factors are involved, including climate, soil, cultivar and human practices. Dutchman Kees van Leeuwen is Professor of Viticulture at the University of Bordeaux. He is among the world’s leading experts on viticultural issues, and particularly on the terroirs of Bordeaux. He is also technical consultant at the prestigious Château Cheval Blanc in Saint-Emilion, where he lives.
  • 3. an issue, the trade moved to the much more favourable climate of southern France. In the Middle Ages, two vineyards close to La Rochelle and Bordeaux did a brisk trade with England and Holland. But the soils at La Rochelle were poor for wine-growing, and were abandoned with the decline of the port; Bordeaux survived, despite its port’s decline, because the soil, climate and cultivars used around the city were ideal for the production of high-quality wines. Still today, new vineyards develop where the socio-economic context is right. The Pic Saint-Loup area in Languedoc-Roussillon is an attractive site for investors – the countryside is beautiful, Montpellier and the Mediterranean are close. In Australia, early settlers bringing vine cuttings via Sydney introduced wine- growing to the Hunter Valley, despite its inaus- piciously humid climate. Later, wine-growing moved to more favourable sites, although the vineyards in the Barossa and Yarra Valleys developed principally because they were close to Adelaide and Melbourne. Bordeaux started to produce “wines of origin” because of its trade with England. Until the 17th century, Bordeaux wines were named after the local parish. Some origins were known to produce better wines than others, and their wines were priced accordingly. In the 17th century, Arnaud de Pontac of Château Haut-Brion started to sell his wines under his estate’s name. Convinced that his wines were superior to other Pessac wines, he raised their prices accordingly. When de Pontac’s son opened a tavern in London, Haut-Brion became an instant hit and, in 1677, the English philosopher John Locke visited Haut-Brion, later writing: “The vine de Pontac, so much esteemed in England, grown on a rising open to the West, in a white sand mixed with a little gravel, which one would think bear nothing; but there is so much a par- ticularity in the soil, that at Mr Pontac’s near Bordeaux the merchants assured me that the wine growing in the very next vineyards, where there was only a ditch between, and the soil, to appearance, perfectly the same, was by no means so good.” Thus, as early as the second half of the 17th century, it was known that soil explained the quality of Bordeaux wines. Inspired by the example of Château Haut- Brion, several other rich Bordeaux merchants of the 17th and 18th centuries created large estates. Some of today’s most famous Médoc estates were among the first to be planted; people had enough empirical knowledge to select the best sites. Qualitative differences – which served as the basis for the 1855 classifi- cation – led to a sophisticated hierarchy in sales prices. Although the classification didn’t evoke such terroir-related factors as climate and soil, the wines from the Médoc châteaux can be considered “terroir wines.” These châteaux produce wines from their own grapes, in vineyards with soils that haven’t budged over years. Wine production today distinguishes “terroir” from “branded” wines. Terroir wines (which include estate and single-vineyard wines) are influenced by the climate and soil of a particular location. Their volume can’t be increased, which is why the more famous terroir wines are good speculative investments. Branded wines, on the other hand, are pro- duced by blending wine or grapes from larger areas and a variety of sources. They are the result of oenological processes and blending, and their volume can be increased to meet demand. Terroir wines have always had excellent traceability – an important issue in the agro- business. Even three centuries ago, a consumer who enjoyed a bottle of Lafite could visit the vines that had produced the fruit, know when the wine was made and bottled and meet the people involved in its production. A vine of many climates A perennial plant, the vine adapts easily to different climatic conditions. Vitis vinifera, the main cultivated species used for quality wines, can survive temperatures as low as -15ºC to -20°C (depending on the cultivar). With cultivars, the temperatures needed for grapes to ripen fully vary considerably. Most early ripening cultivars require at least 1,200 degree days base of 10ºC – a limi- tation on vine cultivation at high latitudes. In equatorial regions, vine vegetation is contin- uous and all the reproductive stages take place simultaneously. Fruit grown under these condi- tions doesn’t make great wines, although it pro- duces commendable table wines. The zone best suited to growing high-quality grapes is between the 35th and 50th parallel latitude of the Northern and Southern hemispheres. In some cases, high altitude compensates for low latitude. How early berries ripen is determined by genes that vary from one cultivar to the next. French researcher Pierre Huglin has calculated the heat requirements of a wide range of cultivars. In the ampelographic collection of Montpellier’s Ecole Nationale Supérieure d’Agronomie, where several hundred cultivars are grown in the same vineyard, there can be –05 – KEES VAN LEEUWEN
  • 4. a two-month time lag between the ripening of the earliest and the latest grapes. In the traditional wine-growing regions of Europe, growers have used this property to adapt their vines to local climatic conditions. At high latitudes, early-ripening grapes produce high- quality wines. Unripe grapes give green, acidic wines with low alcohol levels because the fruit hasn’t accumulated enough sugar. Early ripening varieties such as Pinot Noir, Chardonnay and Gewürztraminer are much more appropriate. At lower latitudes, where the climate is warmer, grapes ripen early in the summer. Quick ripening reduces a wine’s aromatic expression. In 1960, researchers Jean Ribéreau- Gayon and Emile Peynaud noted that “the best wines are produced with cultivars that just achieve ripeness under the local climatic conditions, as if quick ripening of the grapes burned the essences that make the finesse of great wines.” Growers have accordingly planted late- ripening varieties such as Grenache and Mourvèdre at low latitudes in warmer climates. As a result, in Europe’s traditional wine-growing regions, grape-picking generally takes place between September 10 and October 10, despite huge climatic differences between, for example, the Mosel in Germany and Alicante in Spain. This type of viticulture is also called “cool climate viticulture”, not because the climate is particularly cool but because the ripening of the grapes occurs in cool conditions at the end of the summer or in early autumn. Originally, New World viticulturists lacked the experience of Old World growers about what cultivars to choose for what climatic conditions. They usually planted early-ripening varieties in relatively warm conditions. These varieties were chosen as much for marketing as for technical reasons (Chardonnay to pro- duce a white burgundy-style wine, Cabernet Sauvignon to produce a red Médoc-style wine). But although the grapes ripened easily (resulting in high sugar and low organic acid content), they lacked specific aromas. Wine-making technology can compensate for neutrality in grapes, as in the case of most New World Chardonnay wines. Yeasts produce highly aromatic esters (e.g. isoamyl acetate, isobutyl acetate) when alcoholic fermentation takes place at low temperatures. Lactic bacteria produce aldehydes and carbonyl compounds during malolactic fermentation (e.g. diacetyl, which smells like butter). Fermentation in new oak gives vanilla aromas. If the wine-making technology is controlled, early-ripening varieties in warm climates can produce good wines, but because the grapes don’t have a high level of aroma compounds, they lack terroir expression. These wines often taste alike, which is why many wine lovers swear, “Anything but Chardonnay.” Greater experience is why there is more cool climate viticulture in the Old than in the New World and, consequently, more wines expressing terroir. New World viticulturists are beginning to seek out cooler areas, such as California’s Carneros region north of San Francisco where the cool influence of the bay is greater than in the Napa Valley, or the coastal region near Monterrey. In Australia, the rela- tively cool Yarra Valley (north of Melbourne) and Western Australia are fast developing regions. New Zealand Sauvignon Blanc shows how powerfully aromatic this variety can be when grown in cool conditions. Another look at climate Climatic variability within a wine-growing region can be described as mesoclimatic vari- ability. When it is the result of relief (altitude, aspect, slope), it is called topoclimatic vari- ability. Topoclimate can be a major terroir factor in cool regions, where grapes ripen with more difficulty. The Mosel Valley in Germany, for instance, can only produce quality wines on steep, south-facing slopes. In Burgundy, the best wines are produced in the Côte d’Or, at approx- imately 300 metres above sea level. In the higher Hautes-Côtes, it is harder for grapes to reach complete ripeness. Picking is delayed by 10 days, and wine quality is generally good but rarely outstanding, despite the fact that this part of Burgundy has some fine vine-growing soils. Soil type and canopy management can affect microclimatic conditions, and can have a serious impact on a vineyard’s performance. Dry soils (such as stony soils) warm up faster than wet soils and induce early ripening. Night temperatures are cooler close to the ground, but day temperatures are higher. When a cultivar has a hard time ripening in the given climatic conditions (like Cabernet Sauvignon in the Bordeaux area), low vine training can improve quality, although it also increases the vine’s susceptibility to spring frost. –07 – KEES VAN LEEUWEN “Experience explains why there’s more cool climate viti- culture in the Old World and thus more terroir wines”
  • 5. alkaline limestone soils (Ausone), acidic grav- elly soils (Lafite-Rothschild), neutral gravelly soils (Cheval Blanc) and heavy clay soils (Petrus, Cheval Blanc). It is difficult to equate the soil map of a given region with a map of wine-growing quality potential. It’s all about dosage The agronomical approach considers the inter- action between soil and vine. The temperature in the root zone, and mineral and water sup- plies, influence the behaviour of the vine and the quality of the wine. The research undertaken by Barbeau and others has demonstrated that vine precocity, especially at bud-break, is linked to the tem- perature of the soil in the root zone. It is high in dry and shallow soils and low in deep, humid soils. In cool climates, vine precocity can be an important quality factor, as in the Loire Valley, where it is difficult to ripen Cabernet Franc in cool vintages. Nitrogen is the mineral element that most influences vine vigour, yield and grape ripen- ing, and many studies have looked into how much is needed. Other studies deal with the depressive effect of cover crops on nitrogen supply, which goes some way to explaining the quality-improving effect of this technique in red wine production. Much less well docu- mented in scientific literature is the fact that a vine’s nitrogen uptake is likely to vary consid- erably according to a particular soil’s content in organic matter. Soil organic matter turnover depends on soil temperature, aeration, pH and moisture content. It is also very much slowed down by the presence of active limestone. As a result, one of the components of terroir is the level of natural soil nitrogen supply to the vines; the soil types make this highly variable. Xavier Choné et al. demonstrated that lim- ited nitrogen supply to the vines due to soil parameters increases quality in red wines because it reduces the vine’s vigour and increases the berry and wine phenols. This is not true of white wines, where there is a greater need for vine nitrogen supply to obtain a high aroma potential in grapes. To drink or not to drink? Vine water status depends on climate (rainfall and potential evapo-transpiration), soil (water holding capacity) and training system (canopy architecture and leaf area). Vine water uptake conditions are key to understanding the effect of terroir on the quality of the grape, because –08 – TONG N° 2 In warm climates, with early-ripening varieties, high vine training delays the ripening of the fruit. Soils inducing low vine vigour (for instance, because of low water/nitrogen avail- ability) improve light penetration inside the canopy and on to the fruit zone, which is essential for growing high-quality fruit. Rock ’n’ roll Vines can grow on a huge variety of soils. In deep, rich soils, they are vigorous and high- ly productive, although the better wines are generally produced on poor soils. Soil’s effect on vine behaviour and grape composition is complex because it influences both mineral nutrition and water uptake, but also root depth and temperature in the root zone. Soils can be studied from geological, pedological and agro- nomic perspectives. Geology deals with rock types and the dating of sedimentary strata, and acts indi- rectly on topography. Soil type is also related to the sort of rock on which it has developed. In some regions, there is a strong correlation between geological sediment and the quality of the wines produced on it. The most commonly cited example is Chablis. All the famous vine- yards are planted on Kimmeridgian limestone and marl, while vineyards on Portlandian lime- stone produce the less famous Petit Chablis. The influence of the rock type on the geomor- phology of the region is undoubtedly crucial. South- and east-facing slopes are shaped in the soft Kimmeridgian limestone and marl, providing good sun exposure and compensat- ing for the cool climate of the Chablis region. The harder Portlandian rock is found at higher altitudes on wind-exposed plateaux, where it is harder for Chardonnay grapes to fully ripen. In most other regions, the link between geology and a wine’s quality is more obscure. In Bordeaux, very good wines are produced on sediments of varied geological origin: Oligocene-heavy clay sediments, Oligocene limestone and Quaternary alluvium. Some of the finest wines are produced on Oligocene Asteries limestone in Saint-Emilion, while lesser wines are made on the same rock type in the Entre-Deux-Mers region. Soil types can be mapped according to a pedological classification. Some types, including limestone soils, are known to pro- duce high-quality wines, while others, like soils subject to water logging, are not. Yet, across the world, outstanding wines are grown on a huge variety of soils. In the Bordeaux area, top wines are produced on soils as different as
  • 6. the main terroir factors are involved and inter- act (climate, soil, grapevine). Gérard Seguin was the first scientist to study vine water uptake, using a neutron moisture probe in the soils of the Haut-Médoc. He demonstrated that a grape’s quality potential was related to regular but moderate water supply to the vines. In non-irrigated field conditions where vines face water deficits, berries are smaller and total phenols higher. The result is good grape quality potential for red wines, but lower yields. Berries ripen faster when the vines have less water. If there is a severe lack of water, the aroma potential of white grapes can lessen. Irrigation can modify vine water uptake, increasing not only the production of sugar and skin phenols per vine, but also yield. Yield gen- erally increases more rapidly than sugar and skin phenols on a per vine basis, sometimes resulting in dilution. In dry regions, only deficit irrigation can produce economically acceptable yields with high-quality potential grapes. Irrigation is likely to modify terroir expression. The ideal water status is highly dependent on yield. In dry farmed vineyards in dry areas, excellent red wines can be made from fruit grown on severely water-stressed vines, as long as the yield is very low. For higher yields, the best results in terms of quality are obtained when the water deficit is mild, as through deficit irrigation. Privation is the way to the best terroir The highest expression of terroir is obtained in cool-climate viticulture, when the precocious- ness of the grapevine variety allows the fruit to ripen at the end of the growing season (the end of September in the northern hemisphere). For full ripeness, early-ripening varieties are suited to cool climates and late-ripening varieties to warmer climates, so that grape ripening doesn’t occur during the hottest summer months. In order to obtain high grape-quality for red wines, the vine’s vigour and berry size must be controlled, and its grape skin phenols increased. In most terroirs known for high- quality performance, the limiting factor is mild water deficit, either because the climate is dry or because the soil water holding capacity is low – usually because of high pebble content or shallow soil. Hence, high-quality potential viticultural soils are either stony or shallow. In the case of red wines, low nitrogen supply in the soil can also be a quality factor. For white wines, water and nitrogen supply to the vines should be moderate at least, because severe stress can harm the grape’s aroma potential. Sources BARBEAU, G., MORLAT, R., ASSELIN, C. and JACQUET, A. (1998a) «Relations entre la précocité de la vigne et composition des baies de divers cépages du Val de Loire», Progrès Agricole et Viticole, 6, 127-130. BARBEAU, G., ASSELIN, C., and MORLAT, R. (1998b) «Estimation du potentiel viticole des terroirs en Val de Loire selon un indice de précocité du cycle de la vigne», Bulletin de l’O.I.V., 805-806, 247-262. BELL, A., OUGH, C., and KLIEWER, W. (1979) “Effects on must and wine composition, rates of fermentation, and wine quality of nitrogen fertilization on Vitis vinifera var. Thompson seedless grapevines”, American Journal of Enology and Viticulture, 30, 124-129. CARBONNEAU A., 1980. « Recherche sur les systèmes de conduite de la vigne. Essai de la maîtrise du microclimat et de la plante entière pour produire économiquement du raisin de qualité », Thèse Docteur-Ingénieur, Université Bordeaux II, 240pp. CHONÉ, X., VAN LEEUWEN, C., CHÉRY, Ph., and RIBÉREAU-GAYON, P. (2001a) “Terroir influence on water status and nitrogen status of non irrigated Cabernet Sauvignon (Vitis vinifera): vegetative development, must and wine composition”, South African Journal of Enology and Viticulture, 22, 8-15. 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