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 i n ra station in Colmar have already observed a high degree of variability in terpene alcohol content and the oxides of these alcohols.
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