Monitoring of the Oxidation–Reduction Potential and Its Effects on the Chemical Composition of Grenache, Syrah, and Mourvèdre Wines and Their Blends

Oxidation–reduction potential (ORP) is frequently used as an indicator of oxygen exposure during red wine fermentation, but its role as a control variable across grape varieties and blending is not understood. In this study, alcoholic fermentations of Grenache (GR), Syrah (SY), and Mourvèdre (MO) were conducted in quadruplicate under three ORP protocols: control (no ORP setpoint), oxidative (+50 mV ORP setpoint), and reductive (−80 mV ORP setpoint), maintained via pump overs in CON and regulated by air sparging in OXI and RED. ORP protocols differed by variety, with GR exhibiting higher and more variable ORP values than SY and MO under equivalent treatments. Concurrently, SY had higher levels of glutathione, whereas GR had higher levels of the grape reaction product. There were specific treatment‐ and variety‐dependent effects on fermentation kinetics, phenolic composition, color, and volatile profiles. The oxidative ORP protocol resulted in faster fermentation rates, reduced flavan‐3‐ol concentrations, anthocyanin losses, yellower color, and lower ester concentrations across varieties. To assess ORP‐driven effects after blending, wines were combined in equal proportions and compared with values predicted by linear averaging. Several phenolic and volatile parameters fell below predicted values, indicating that blending does not always increase chemical parameters. These results demonstrate that the outcomes of contrasting ORP protocols during alcoholic fermentation are relatively variety dependent and can influence wine composition and the chemical outcomes of blending, highlighting the need for variety‐tailored ORP protocols in red winemaking.