The biosynthesis of S-(3-hexan-1-ol)-glutathione (3MH-S-glut) and S-(3-hexan-l-ol)-L-cysteine (3MH-S-cys), which act as flavour precursors in wines, in Vitis vinifera grapes exposed to various environmental stress conditions is reported here. Ultraviolet (UV-C) irradiation, water deficit, and biological stimulation up-regulated 3MH-S-glut and 3MH-S-cys biosynthesis in grape leaves. 3MH-S-glut and 3MH-S-cys contents in grape berries were increased by cold shock, heat shock, UV-C irradiation, and biological stimulation. The results suggest that environmental stress enhances the biosynthesis of both flavour precursors in grapevine. The transcription of VvGST1, VvGST3, VvGST4, and GGT in grapevine exposed to the stress conditions was increased markedly compared with that in control grapevine. Also, UV irradiation increased GST (glutathione S-transferase) and GGT (γ-glutamyl transferase) enzyme activities in grape berries. Recombinant VvGST3 and VvGST4, but not VvGST1, mediated the synthesis of 3MH-S-glut from reduced glutathione and trans-2-hexenal in vitro. The enzymatic mediation of flavour precursor production is a novel function of plant GSTs and may result in the detoxification of damaged grape cells under stress conditions.