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Volatile esters are amongst the most important yeast-derived flavor-active compounds produced during brewery fermentation. Dissolved oxygen concentration has long been recognized as an effector for the synthesis of esters by Saccharomyces spp. Here we demonstrate the effects of oxygen exposure time at vessel filling on the synthesis of esters during fermentation using a series of laboratory-scale experiments. In control fermentations, all the yeast was pitched into 10 L of high-gravity wort. In trial fermentations, all the yeast was pitched at the start of collection and wort was added as three 3.33-L batches or five 2-L batches over 12 or 24 hr, respectively. Wort was oxygenated to 15 ppm of O2 for each experiment and identical pitching rates and temperature profiles were adopted. Compared with the controls, increasing the number of batch fills to three and five reduced the final concentration of isoamyl acetate by 15.7 and 34%, respectively, and ethyl acetate by 25 and 39%, respectively, suggesting that a relationship exists between oxygen exposure time and ester synthesis. In parallel, hydrostatic pressure was applied to each condition, resulting in a further decrease in acetate esters. These data suggest that an inverse correlation exists between vessel size relative to brew length and ester production. Keywords: Acetate esters, Fermentation, Hydrostatic pressure, MCFA ethyl esters, Oxygenation, Vessel filling
