The Role of Climate on Terroir
Emerging Views on the Relationship between Temperature and Soil.
How Climate Affects Grape Ripening.
The traditional view of terroir, celebrated by the French, is that a given vineyard location contributes a unique flavor profile to wine made from grapes grown there. This notion has not been entirely debunked and many New World winemakers continue to espouse it.
Traditional concepts of terroir include climate, vineyard orientation and soil composition. The influence of the chemical composition of vineyard soils upon flavors in wine has been called into question in recent years through studies conducted at the Institut Coopératif du Vin and the Ecole Nationale Supérieure Agronomique in Montpelier, France. According to Professor Jean-Claude Davidian, "Nobody has been objectively able to show any links between the soil's mineral composition and the flavour or fragrance of the wines."
So if grapevines cannot suck up mineral flavors from soils, where do the vast differences in wine flavor and aroma spring from?
The past decade or so has shown great advances in our understanding of how grapes ripen. We now understand that the ripening process involves two different processes.
(1) Photosynthesis. This familiar process involves sunlight falling upon vine leaves and stimulating chloroplasts to produce color and sugar. Photosynthesis ceases at sunset, regardless of the ambient temperature.
(2) Phenolic Ripening. Without becoming too technical, polyphenols are those chemicals within grapes that result in specific flavors and tannins. Phenolic ripening is temperature dependent. So even after photosynthesis turns off for the night, phenolic ripening continues on as long as the ambient temperature remains above 50°. This casts a new light on the often promulgated notion that warm days and cool nights represent ideal winegrowing conditions.
Grapes can be fully sugar ripe before they have achieved flavor maturity. This is almost always the case in warm or hot regions. The result is simple wines with little complexity of flavor and aroma. If a grower lets his crop hang till phenolic ripeness is achieved, the sugar levels often rise above desirable levels, resulting in high alcohol wines with intense fruit character. Modern wineries sometimes resort to diluting these wines with water or running the wine through reverse osmosis filters to de-alcoholize them.
What then can be said of the role of soils in viticulture? Since this is an issue not entirely settled by the scientific community, we can only repeat what is being currently said on the matter. The winegrowing community largely holds to the traditional view that grapevines extract flavor elements (not just nutrients) from the soils in which they grow. The academics, who require proofs, are telling us that soils influence grapevines primarily through physical and textural elements, not chemical composition other than pH.
