SO2 reaction with electrophilic species present in wine, including in particular carbonyl compounds, is responsible for the reduction of its protective effect during wine aging. In the present study, direct 1H NMR profiling was used to monitor the reactivity of SO2 with acetaldehyde under wine-like oxidation conditions. The dissociation of acetaldehyde bound SO2 was evidenced suggesting that released free SO2 can further act as an antioxidant. EPR and DPPH assays showed an increasing antioxidant capacity of wine with the increase in the concentration of acetaldehyde sulfonate. The presence of acetaldehyde sulfonate in wines was correlated with the overall antioxidant activity of wines. The first evidence of acetaldehyde bound SO2 dissociation provides a completely new representation of the long-term protection efficiency of SO2 during bottle aging.