The contribution of high-molecular-weight melanoidins to the overall antioxidant activity of traditional balsamic vinegar (TBV) has been determined. High-molecular-weight melanoidins are gradually synthesized and accumulated during TBV aging contributing significantly to the browning of the vinegar. The increase in antioxidant activity of TBV during aging is largely because of the formation of high-molecular-weight melanoidins and only in lesser part to the concentration of polyphenols deriving from the grape or to the formation of low-molecular-weight Maillard reaction or caramelization products during must cooking and vinegar aging. During aging, low-molecular-weight compounds are progressively incorporated into the melanoidins skeleton and may contribute significantly to the antioxidant activity of high-molecular-weight melanoidins. Among these compounds, it has been shown that antioxidant phenolic compounds are progressively incorporated into the melanoidins skeleton during TBV aging.