The openness of the landscape is a crucial factor in winemaking.
THE WORLD OF WINE AND VINE so little doubts the existence of differences in the overall natural environment—the terroir, as it is called—of winegrowing regions that it has made them the basis for awarding protected designations of origin. Is this justified? Agronomists are accustomed to examining how the particular features of a given viticultural site—its climate, soils, and parent rock—affect the growth of its vines. Éric Lebon and his colleagues at the Institut National de la Recherche Agronomique (INRA) station in Colmar have studied defined sections of the Alsatian landscape and shown that its openness is at least as important as its capacity for retaining groundwater and exposure to sunlight.
Wine growers seek to plant grapevines in conditions that favor the formation of berries, rather than leaves or branches, and the accumulation of sugars (for fermentation) and aromas. Berries are able to ripen before the intemperate weather of autumn causes them to rot only if the vines have begun to grow early enough. For this reason it was long thought that sunshine was the chief advantage of good terroirs.
At the request of the Centre Interprofessionel des Vins d’Alsace, the Colmar agronomists continued research that had been begun in the 1970s in the Bordeaux region by Gérard Seguin and his colleagues at the Institut d’Œnologie there. The team led by Seguin analyzed the importance of the soil, and the way in which it nourishes the vine with water, in promoting the vine’s growth. The best terroirs, it found, enjoyed a regular supply of water and periods of only moderate drought, conditions that encourage the early ripening of the grapes.
Beginning in 1975, René Morlat and his colleagues at the INRA station in Angers studied the land in the legally protected red wine–producing vineyards of the Loire Valley (Cabernet Franc from Saumur-Champigny, Chinon, and Bourgueil). Their work confirmed the earlier observations and showed that the more rapidly the soil heats up in the spring, the earlier the vine develops and the more favorable the landscape is to successful cultivation. The Angers agronomists suspected that the relevant climatic characteristics could be analyzed in terms of a landscape’s openness, determined by measuring the angle of the horizon in relation to a horizontal axis for the eight principal directions of the compass dial. Vines were supposed to develop differently in a basin, where the degree of openness is low, than at the top of a hill, where the degree of openness is high. Lebon and his colleagues tested this assumption in the vineyards of Alsace, which are semicontinental (and so quite different from those of Bordeaux and the Loire Valley), in an area lying between Witzenheim and Sigolsheim, near Colmar.
The soils and parent rock of Alsace had already been extensively studied but never on the scale of the experiment now contemplated. Over an area of 1,750 hectares (4,325 acres) Lebon and his colleagues carried out a hectare-by-hectare survey to determine homogeneous pedological units. On the basis of various criteria for characterizing types of soils, they distinguished some thirty homogenous units. A pit was dug in each of these zones to analyze soil types.
Landscape and Climate
Lebon and his colleagues made climatological measurements at stations set up near pits dug in vineyards in which the Gewurtztraminer grape was cultivated and observed that local climates varied little, on an annual average basis, from unit to unit. Significant variations occurred only on shorter time scales. During periods of inclement weather, for example, the air temperature was found to depend only on altitude; in clement weather the diurnal temperature varied as a function of altitude, declivity, orientation, the height of the horizon from east to west, and the thermal properties of the soils. Taken together these measurements define mesoclimates, which is to say climates on the local scale of a slope or valley bottom, for example. Comparing the various landscape indices with the climatological data made it possible to refine the notion of terroir. Temperature turned out to be important in determining the mesoclimate, but not as important as the landscape.
What makes a terroir good for growing wine? The INRA agronomists showed that in Alsace, more than in the Bordeaux region or the Loire Valley, the principal differences result from variations in the maturity of the grapes at the moment of harvest. In all the wine-growing regions studied, water nourishment conditions played a major role in determining, among other things, the length of time between the fruiting of the vine and the ripening of the grapes. Maturation comes late when water is plentiful because the vine produces leaves rather than berries. When the supply of water is insufficient, maturation is delayed as well, but the adage that the vine must be made to suffer if it is to produce grapes is only partly true: The supply of water should decline both moderately and regularly.
Now that the notion of terroir has been validated in Alsace, it remains to study the relationship between a wine-growing site’s total natural environment and the quality of the wines it produces. Attempts to characterize aromas are under way: Alex Schaeffer and his colleagues at the INRA station in Colmar have already observed a high degree of variability in terpene alcohol content and the oxides of these alcohols.