By Harold McGee
In the second, “trickling” method, the wine is poured repeatedly over a porous, air-rich matrix—wood shavings, or a synthetic material—onto which the acetic bacteria cling. This greatly increases the effective surface area of the wine, and regularly exposes all parts of the liquid to both oxygen and bacteria. The result is a quick fermentation that takes only a few days. Finally, there is the “submerged culture” method, in which free-swimming bacteria are supplied oxygen in the form of air that is bubbled through the tank. This industrial method converts the liquid’s alcohol into acetic acid in 24–48 hours.