Vinegar and Acetic Acid

The aerobic bacterial oxidation (by the genus Acetobacter) of alcohol to dilute acetic acid (8 %) is another ancient procedure, furnishing vinegar, a flavored acetic acid solution, fermented from wine, either, malt, or dilute alcohol. If pure dilute alcohol is fermented, pure dilute acetic acid results. The yield is 80 to 90% of theory. Air must be supplied, as these formulations indicate:

2 C₂H₅OH + O₂ -------- 2 CH₂CHO + 2 H2O
2 CH₃CHO + O₂ ------- 2 CH₃COOH

Since these reaction are exothermic, the alcohol can be slowly trickled through either the apparatus, letting the heat dissipate, or it can be recirculated with special cooling. It cider, malt, or wine is fermented, the acetic acid content of the resulting vinegar rarely exceeds 5 % because of limitations of the sugar content: if dilute alcohol is the raw material, the acetic acid may rise to 12 or 14% at which acidity the bacteria cease to thrive. If a fruit juice is turned to vinegar, certain eaters are formed, varying with the raw material and thus imparting a characteristic flavor. Synthetic acetic acid is made from ethylene, or by treating methanol with carbon monoxide.