Effects of Hyperbaric Micro-Oxygenation on the Colour, Total Phenolic Content, Volatile Composition, and Sensory Profile of Vitis vinifera L. cv. Monastrell Grape Must

Oxygen management during alcoholic fermentation can redirect phenolic reactions and yeast-derived aroma formation, but the use of mild hyperbaric conditions as a micro-oxygenation strategy remains poorly characterized. This study evaluated the effects of hyperbaric micro-oxygenation at 1.40 ATA in a stainless-steel chamber on the fermentation of Vitis vinifera L. cv. Monastrell must, comparing treated and non-micro-oxygenated samples at the initial, mid-fermentation, and final stages. Physicochemical parameters, CIELAB color coordinates, total phenolic content, volatile organic compounds, and descriptive sensory attributes were analyzed. Hyperbaric micro-oxygenation did not impair fermentation completion, as both treatments reached final residual sugar values of 2.2 g/L and alcohol contents of 15.2–15.4% v/v. The treatment promoted a darker final chromatic profile, with lower L*, the highest overall color difference, and a marked increase in total phenolic content, reaching 1900.9 mg gallic acid equivalents/L compared with 1593.2 mg gallic acid equivalents/L in control. Volatile changes were compound, and stage-dependent, indicating modulation rather than generalized enhancement of aroma formation. Ethyl esters, particularly ethyl octanoate and ethyl decanoate, increased markedly under micro-oxygenation, while acetate esters such as ethyl acetate and hexyl acetate decreased relative to the initial must, reflecting a shift in the balance of aroma-active compounds rather than a uniform increase across all volatile families. These findings support mild hyperbaric micro-oxygenation as a promising non-thermal strategy to modulate Monastrell fermentation quality.