Aroma and Aroma Precursors in Grape Berry

The grape berry is the site of biosynthesis and accumulation of compounds that are likely to contribute in wines some of their aromatic characteristics. These compounds have the aromatic potential, and exist in part as volatile forms but mainly as non-volatile aroma precursors that can be released through chemical and biochemical reactions during vinification and ageing. The chemistry of aromas has gradually identified a number of key volatile compounds and their precursor forms. Among these compounds, we have considered methoxypyrazines, monoterpenes and C13-norisoprenoids, which are derivatives of carotenoids and sulfur compounds possessing a thiol group. They represent a large diversity of flavour nuances (herbaceous, fruity, floral, empyreumatic, etc.), often at trace concentrations (in the nanogram per litre range). The reactivity of these compounds in enological conditions, and the state of the knowledge on their biosynthesis in grapes, both in volatile form, possibly odorous, and in precursor form (glycosylated or conjugation of cysteine and glutathione) are described.