Acetic acid is the final oxidation product of ethanol via the intermediate stage of acetaldehyde. The fermentation of ethanol in the presence of oxygen under the influence of vinegar bacteria (Acetobacter) was already known in the antique, leading to the so-called vinegar. The anhydrous acetic acid is called glacial acetic acid, an inflammable liquid (melting point of 17 oC, boiling point 118 oC). The density is 1.05 g/cm3, pH (10 g/l, H2O, 20 oC) 2.5. The salts of acetic acid are called acetates.
Household vinegar contains 4 to 5 percent acetic acid, produced from alcoholic solutions deriving from wine grapes or apples but also from synthethic alcoholic solutions. Balsamic vinegar (Aceto balsamico) is a wine vinegar, matured at least for 3 years and up to 25 years in wooden barrels.
By alcohol consumption of humans the resulting blood alcohol level is also converted to acetic acid via the intermediate stage of acetaldehyde, with is then further oxidized under the participation of the enzyme aldehydedehydrogenase (ALDH) to acetic acid, which plays in activated form (acetylcoenzyme A) an important role as metabolic product.