Aroma trajectories under climate pressure: how must pH shifts reshape alcoholic fermentation (AF) VOCs pathways and final wine sensory profiles

Abstract

Climate change (CC) is altering grapes and must by affecting technological performance and wine quality(1), including VOCs and sensory features(2). Under the current CC, the increased pH(3) may modulate VOCs formation during AF and impact their evolution over time with consequences on wine aroma quality and typicality. This study investigates how pH variations influence formation kinetics of VOCs during AF of a must and sensory quality of the final wine. A Falanghina white grape must was adjusted at increasing 3 pHs (3.2-3.5-3.8) representative of the current CC-related pH-shift and fermented at 16 °C in batch micro-vinifications (3 replicates per pH). During AF, 64 VOCs were isolated by LLE at 7 sampling times (Days: D0-3-7-10-14-22-25) and quantified (calibration curves) by GC/MS (triplicate). At D25, 15 trained subjects evaluated olfactory and taste attributes of the final wines by RATA sensory method (duplicate). Preliminary results suggest that, across all pHs, total VOCs rise sharply after AF onset, peak at D7-10, then decline, remaining consistently higher at pH3.8, with compound-specific kinetics and pH effects. Isoamyl acetate peaks at D7 and remains stable, with highest concentrations at pH3.8 (significant at D7). Phenethyl acetate increases early, reaches a maximum at D10, and declines during the late stages, showing consistently higher levels at pH3.8 from D7 onward. Ethyl hexanoate follows a temporal trend like phenethyl acetate without significant pH effects, whereas ethyl octanoate exhibits an evolution comparable to isoamyl acetate. 1-Butanol peaks at D10 and then declines, with significant pH differences observed only at D25 (pH3.8 > 3.5 > 3.2). 1-Hexanol and cis-3-hexenol show early increases (D3) with the highest concentrations at pH3.2 and a decrease at increasing pH, a trend also observed for linalool and α-terpineol, which rise the maximum concentration at D7 that is maintained till the end. PCA on chemical and sensory data of the final wines discriminates samples by pH. pH3.8 clusters with a fruity/banana–mango profile, driven mainly by acetate and ethyl esters. pH3.2 aligns with vegetal/mineral/dried-fruit notes, associated with C6 alcohols, terpenes, and a few lactones. pH3.5 forms a distinct group linked to tropical/balsamic notes, showing fewer VOCs correlations (guaiacol, ethyl valerate). The study provides useful insights for wine fermentation aimed at managing VOCs composition and sensory expression under CC–related pH conditions.

References

1. van Leeuwen, C.; Darriet, P. (2016). The Impact of Climate Change on Viticulture and Wine Quality*. J. Wine Econ., 11(1), 150–167.
2. Mira de Orduña, R. (2010). Climate change associated effects on grape and wine quality and production. Food Res. Int., 43(7), 1844–1855.
3. Plantevin, M.; Merpault, Y.; Lecourt, J.; Destrac-Irvine, A.; Dijsktra, L.; van Leeuwen, C. (2024). Characterization of varietal effects on the acidity and pH of grape berries for selection of varieties better adapted to climate change. Front. Plant Sci., 15, 1439114.