Uneven distribution of thiol precursors across red grape berry compartments shapes wine aroma quality: effects of variety, vintage, and skin composition.

Varietal thiols constitute key aroma compounds in wine and occur in grape berries as odorless precursors. This study aimed to characterize thiol precursor diversity in 32 red grape varieties (Vitis vinifera and hybrids) by examining their distribution across berry compartments and assessing the effects of grape variety, vintage, and skin cell wall composition. Significant varietal differences were observed in thiol precursor content among berry tissues (average of 10.08 ± 15.02 μg/kg in skins, 10.22 ± 9.59 μg/kg in pulps and 0.94 ± 0.89 μg/kg in seeds), providing the first evidence of biosynthetic activity in seeds. Vintage strongly influenced precursor levels in all compartments, with a higher effect in skins, underscoring their central role. The lack of correlation between precursor content in berries and musts may indicate a selective extraction maybe due to interactions with cell wall polysaccharide. Furthermore, no correlation was found between must precursors and volatile thiols in wine, highlighting the complexity of thiol formation.