Changes in (a) pH, (b) acetic acid bacterial counts, and (c) acetic acid content in OFG at each stage of the optimization process for acetic acid fermentation. ●: Control (fermentation without supplementation), ■: condition optimized at stage 1 (fermentation with supplementation of 3% fermentation alcohol), ▲: condition optimized at stage 2 (fermentation with supplementation of 8% sucrose in addition to the condition optimized at stage 1), ◇: condition optimized at stage 3 (fermentation at 25 °C in addition to the conditions optimized at stage 2). Sucrose was selected based on the effects of several carbohydrates at the same concentration, and the sucrose concentration was subsequently optimized. Error bars indicate standard deviations determined from triplicate experiments.