Characterization of varietal effects on the acidity and pH of grape berries for selection of varieties better adapted to climate change

Abstract

Climate change is drastically modifying berry composition and wine quality across the world. Most wine regions with a history of winemaking are suffering from a loss of typicity and terroir expression because of climate change impact on berry components at harvest, including wine acidity, with total acidity decreasing and pH increasing. Such changes can have a major impact on wine stability and quality. One important option for adaptation is the selection of grapevine varieties better adapted to warmer and drier conditions. Weekly measurement of tartaric acid, malic acid, pH and titratable acidity from veraison until maturity were carried out on 51 varieties over seven years in two experimental plots. Varietal differences were shown for the rate of malic acid degradation during the ripening period, with some varieties metabolizing malic acid faster per unit of thermal time than others. Some varietal differences were also noticed regarding tartaric acid modulation, which can occur under exceptionally high temperatures. Differences in the dynamics of pH evolution in grape must over the growing season were evaluated and varieties characterized with regard to organic acids (tartaric acid and malic acid), inorganic compounds (cations) as well as pH levels and stability. This multi-trait approach allows the selection of grapevine varieties based on parameters linked to their acidity, which is of particular importance in the context of climate change.

Keywords: Vitis Vinifera; climate change; grapevine; inorganic cations; malic acid; pH; tartaric acid; varietal traits.

Figure 1

(A) Varietal differences in tartaric acid modulation, expressed as content (μmol/berry), from the 2nd week after veraison until the 8th week after veraison for the 51 varieties of the VitAdapt and La Tour Carnet experimental plots from years 2017 to 2023. (B) Varietal differences in tartaric acid decrease for the 51 varieties of the VitAdapt and La Tour Carnet experimental plots from years 2017 to 2023. The more negative alpha_tar, the higher the rate of decrease during grape ripening. Letters in the right column indicate statistically significant differences assessed with Tukey test. The black vertical line in each bow represents the median value. Colors represent the vintages, as displayed on the legend of panel (A).

Figure 2

(A) Varietal differences in malic acid degradation for the 51 varieties of the VitAdapt and La Tour Carnet experimental plots from years 2017 to 2023 from the 1st week after veraison until the 8th week after veraison. (B) Varietal differences in malic acid degradation for the 51 varieties of the VitAdapt and La Tour Carnet experimental plots from years 2017 to 2023. The more negative alpha_log_mal, the higher the rate of degradation during grape ripening. Letters in the right column indicate statistically significant differences assessed with Tukey test. The black vertical line in each bow represents the median value. Colors represent the vintages, as displayed on the legend of panel (A).

Figure 3

Relative contribution of the variance explained by inorganic cations, malic acid and tartaric acid of a mixed model assessing the drivers of grape must pH in weeks 2 to 8 after mid-veraison (all varieties considered together).

Figure 4

Relative contribution of the variance explained by inorganic cations, malic acid and tartaric acid of a mixed model assessing the drivers of grape must pH in weeks 2 to 8 after mid-veraison (each variety considered separately).

Figure 5

Principal Component Analysis of the alpha_log_mal, alpha_tar, malic acid impact on pH (Malic Acid – pH), inorganic cations impact on pH (Cations – pH) and tartaric acid impact on pH Tartaric Acid – pH). Ellipses are drawn around each variety barycenter (variety names were not added to the figure because it would harm clarity).

Figure 6

Hierarchical clustering analysis (HCA) of the 46 varieties from the VitAdapt plot based on average pH at five weeks after veraison, alpha_log_mal, alpha tar, inorganic cations impact on pH, malic acid impact on pH and tartaric acid impact on pH. Heatmap represents the scaled value for each variety on each component. HCA was implemented using the Ward method based on Euclidean calculations.