Abstract Hand- and machine-harvested ‘Stover’ (a white Euvitis hybrid) and ‘Noble’ (a red Vitis rotundofolia cultivar) grapes were either treated with 100 mg SO2/kg (applied as potassium metabisulfite, K2S2O5) or not treated and held at ambient temperature (≈25°C) for 0, 24, and 48 hr after harvest. Raw fruit and wine quality from each treatment were evaluated. ‘Noble’ grapes of all treatments held for 24 hr had developed signs of microbial spoilage, and the machine-harvested grapes held without SO2 had the most. However, only the machine-harvested ‘Stover’ grapes held without SO2 had began to deteriorate during 24 hr. Grapes of both cultivars had deteriorated after 48 hr, but SO2 limited the deterioration of both machine- and hand-harvested grapes. In general, machine-harvested grapes deteriorated to a greater extent than hand-harvested grapes. Wines made from ‘Noble’ grapes that had been held for 0 or 24 hr had similar quality, but machine-harvested ‘Stover’ grapes held for 0 to 24 hr without SO2 produced a poorer wine than the other treatments. Wines from machine-harvested grapes held for 48 hr had poorer quality than wines from hand-harvested grapes. Postharvest additions of SO2 improved the quality of wine from machine-harvested but not hand-harvested fruit held for 48 hr.