Wines & Vines

August 2017 Closures Issue

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52 WINES&VINES August 2017 WINEMAKING PRACTICAL WINERY & VINEYARD T erroir is a cultivated ecosystem in which grapevines interact with soil and climate. The main climatic pa- rameters include temperature, rain- fall and reference evapotranspiration. Vine phenology and grape ripening is mainly driven by air temperature and soil tempera- ture. The soil provides water and minerals to the vine, particularly nitrogen. In the past several decades, tools have been developed to quantify terroir parameters. Small- scale weather stations can yield temperature data at high resolution, which can be used to provide refined maps of temperature summa- tions. Models have been developed to predict phenology in relation to temperature. Vine water status can be assessed with a pressure chamber, or by means of carbon isotope dis- crimination measuring grape sugar (so-called δ 13 C). 12 Vine nitrogen status can be assessed with measurement of yeast assimilable nitrogen (YAN). In this way, terroir parameters can not only be measured but also mapped. This approach allows precise vineyard management to optimize terroir expression through plot selection, choice of appropriate plant material in relation to soil and climate, vineyard floor management, fertilization and training system. Defining terroir Wine quality depends on the environmental characteristics of where the grapes are grown. Many factors are involved such as climatic condi- tions, soil composition (geology, soil type and soil depth) and topography. All these factors act si- multaneously, and they interact. If each terroir factor is studied separately, studies remain highly descriptive and fail to explain why wine shows such extraordinary sensory diversity. Moreover, terroir factors like soil and climate are complex and need to be broken down to enable studying their impact on vine develop- ment, grape ripening and wine composition. This multidisciplinary approach is the basis of Gérard Seguin's definition: "Terroir is a (culti- vated) ecosystem, in a given place, in which the vine interacts with the natural environment and, in particular, the soil and the climate." 8 Human factors also play an important role in terroir expression. 11 In this text, major fac- tors involved in terroir expression are ad- dressed at different scales. They can be managed by the appropriate choice of plant material and viticultural practices in order to optimize terroir expression in winegrowing areas with a wide range of climatic conditions and soil characteristics. Major environmental factors involved in terroir expression Among the environmental factors acting on vine development, phenology, grape ripening and wine composition, three are of major importance: air and soil temperature, vine water status and vine nitrogen status. Each can be measured at different scales. They can also be mapped, which is the ultimate tool to implement fine-tuned management at the parcel scale, or even at the intra-parcel scale. Air and soil temperature Vine development and phenology are closely related to air temperature. High temperatures trigger early phenology. Timing of the ripen- ing period is critical in the production of terroir wines. If ripeness occurs too late (after Oct. 15 in the Northern Hemisphere), grapes may struggle to reach full ripeness, particu- larly in regions where the temperatures drop quickly during October. In those situations, wines made from grapes harvested after Oct. 15 may be acidic and green. If ripening hap- pens too early (in July or August), the timing of technological ripeness (sugar/acid bal- ance), aromatic ripeness and phenolic ripe- ness in grapes are uncoupled. Wines produced under these conditions are unbalanced while they generally lack freshness and aromatic complexity. Hence, the ideal window to reach full ripeness is approximately Sept. 10-Oct. 15 in the Northern Hemisphere. 11 Understanding Terroir Expression How to optimize vineyard-management practices By Cornelis van Leeuwen, Jean-Philippe Roby and Laure de Rességuier Soil electric tomography is used to create a soil resistivity map (left). The soil map for a winegrowing estate in Bordeaux, France (right) was created by implementing classical tools (auger sampling, soil pit study, soil analyses), but precision was increased by using the boundaries of the soil-resistivity map. MAP FAR LEFT: GEOCARTA, 75002, FRANCE. MAP NEAR LEFT: VAN LEEUWEN, ROBY, MARGUERIT AND DE RESSÉGUIER, UNPUBLISHED USE OF SOIL ELECTRIC TOMOGRAPHY Sandy/gravelly soil Sandy/gravelly soil over clay loam Sandy/gravelly soil over clay loam with non-permanent water logging Sandy/gravelly soil over lime-holding clay loam with non-permanent water logging Gravelly/sandy soil Gravel Gravel with high organic matter content Gravel with high organic matter content over clay-holding gravel Soil with permanent water table Ohm.m 20 63.25 200 632.46 2,000 % 2.2 1.1 0 125 250 meters 0 125 250 meters

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