Climate change – variety change?

Climate change poses a significant challenge for global viticulture, with growing evidence of its negative impact on thermal and hydric regimes, both of which are essential for the development of table grapes.

The current climate changes are directly threatening the balance of the vineyard at harvest time. The maturation period of the grapes is shifted to the middle of the summer, at a time when radiation and air temperature are at their maximum. In this context, the implementation of corrective practices becomes problematic. Unfortunately, our knowledge of the climate effect on the quality of different grape varieties remains very incomplete to guide these choices. During the Innovine project, original experiments were carried out on Syrah to study the combined effects of normal or high air temperature and varying degrees of exposure of the berries to the sun. Berries subjected to these different conditions were sampled and analyzed throughout the maturation period. Several quality characteristics were determined, including anthocyanin content. The objective of the experiments was to investigate which climatic determinants were most important for anthocyanin accumulation in the berries. Temperature and irradiance data, observed over time with a very thin discretization step, are called functional data in statistics. We developed the procedure SpiceFP (Sparse and Structured Procedure to Identify Combined Effects of Functional Predictors) to explain the variations of a scalar response variable (a grape berry quality variable for example) by two or three functional predictors (as temperature and irradiance) in a context of joint influence of these predictors. Particular attention was paid to the interpretability of the results. Analysis of the data using SpiceFP identified a negative impact of morning combinations of low irradiance (lower than about 100 μmol m−2 s−1 or 45 μmol m−2 s−1 depending on the advanced-delayed state of the berries) and high temperature (higher than 25oC). A slight difference associated with overnight temperature occurred between these effects identified in the morning.

A critical aspect of wine quality from a consumer perspective is the overall impression of wine flavour, which is formed by the interplay of volatile aroma compounds, their precursors, and taste and matrix components. Grapes contribute some potent aroma compounds, together with a large pool of non-volatile precursors (e.g. glycoconjugates and amino acid conjugates). Aroma precursors can break down through chemical hydrolysis reactions, or through the action of yeast or enzymes, significantly changing the aroma profile of a wine during winemaking and storage. In addition, glycoconjugates of monoterpenes, norisoprenoids and volatile phenols, together with sulfur-conjugates in wine, provide a reservoir of additional flavour through the in-mouth release of volatiles which may be perceived retro-nasally.

Dimethyl sulfide (DMS) is a low molecular weight sulfur compound produced in wine during aging by the chemical degradation of S-Methyl-L-methionine (SMM). Investigating the aromatic profile of Amarone commercial wines from different wineries, it was found that DMS presented a high variation in concentration across wine samples ranging from 2.88 to 64.34 μg/L, which potentially can

Work aimed at understanding the relationship between a terroir, in the agronomic sense, and the physico-chemical characteristics of grapes or wine are numerous today, as evidenced by the program of this symposium. But for an economist, the central question remains to know how the terroir can intervene in the construction of the economic value of wine and in the differentiation of its prices. Is the terroir effect recognized by the end consumer or is it only an internal adjustment variable in the production systems? Through which indicators can this terroir effect be managed by the various operators in the sector? In the end, isn’t it better to invoke a “territorial effect” that the actors can build, and of which the terroir would be one of the possible components?