Vinegar having an acetic acid concentration higher than 20 percent weight by volume is produced in a submerged fermentation by maintaining the temperature of a fermenting broth at 27.degree.-32.degree. C. until the acetic acid concentration of the fermenting broth (after the initiation of fermentation) reaches 12-15 percent weight by volume. Then the temperature of the fermenting broth is lowered by 0.5.degree. C. to 2.degree. C. Fermentation is continued at the lower temperature until the concentration of acetic acid increases by between 0.05 to 2 percent weight by volume. At this time, the temperature is again reduced by from 0.5.degree. C. to 2.degree. C. The fermentation is continued, with subsequent temperature reductions of from 0.5.degree. C. to 2.degree. C. each time that the concentration of acetic acid in the fermentation broth increases by 0.05 to 2 percent weight by volume over the highest concentration found in the course of the fermentation at the preceeding temperature stage, until the desired concentration of acetic acid is obtained. However, at no time is the temperature of the fermenting broth allowed to fall below 20.degree. C.