Vinegar

VINEGAR (from the Greek oxys—sharp), Acetum, an aqueous solution of acetic acid. Technically, it can be obtained by simple dilution of synthetic acetic acid or acetic essence obtained during the dry distillation of wood, or by fermenting weak alcohol solutions (in practice about 10% C₂H₅OH) with acetic acid bacteria (see Fermentation); among the latter, the most unpretentious and active is Mycoderma Aceti. The acetic acid fermentation process is aerobic; schematically it is represented as: CH₃CH₂OH + O → CH₃CHO + H₂O alcohol

acetaldehyde CH₃CHO + O → CH₃COOH acetic acid Therefore, acetic acid fermentation requires aeration. The vats in which fermentation is carried out are loaded with wood shavings in order to provide a large contact surface between the fermenting liquid and air. According to a number of scientists, the oxidative process proceeds only to the formation of acetaldehyde (I), which then undergoes acetoin condensation; acetoin (II) yields ethyl acetate (III) upon intramolecular rearrangement, which hydrolytically decomposes into acetic acid (IV) and alcohol (V): CH₃CHO + HCOCH₃ I

I CH₃CHOHCOCH₃ II CH₃CH₂OCOCH₃ (+H₂O) HOCOCH₃ + CH₃CH₂OH IV

V This scheme easily explains the fact that the fermentation of alcohol never goes to completion (in reality, new alcohol molecules are ultimately formed); ethyl acetate (III), which causes the specific aroma of such vinegar, and acetoin (acetyl methyl carbinol, II) can always be found in fermented vinegar. Chemical differentiation of vinegar obtained by fermentation from vinegar made from essences (obtained by dry distillation of wood) is based on the detection of the latter in the distillate of vinegar. In commerce, distinctions are made between wine vinegar (grape wine subjected to acetic acid fermentation), spirit vinegar, and beer vinegar; special table vinegars are obtained by infusing ready-made vinegar with spices (bay leaf, marjoram, etc.), among which “tarragon” vinegar, infused with tarragon herb (Herba Dracunculi), is popular. In medicine, vinegar was formerly used for the preparation of sour mixtures or saturations intended to exert a cooling (antipyretic) effect; externally, it was used for lotions and cooling compresses for headaches and bruises. Vinegar possesses a weak antiseptic action due to its acidity, which is why it is used for preserving food products (pickling). Medical vinegars formerly in use (Aceta medicinalia), chief among them aromatic vinegar (Acetum aromaticum), were tinctures on various medicinal plant materials (Acetum Scillae on squill, Acetum Sabadillae on sabadilla seed, Acetum aromaticum on aromatic roots with added essential oils, etc.); they have fallen out of use and been replaced by more expedient alcoholic extracts. Officinal pharmacopoeial vinegar contains 6% acetic acid; commercial vinegars occur with a content ranging from 3% to 9%. For internal use, wood vinegar containing toxic impurities (methyl alcohol, aldehydes, etc.) must not be used. On the relative harmlessness and assimilability of vinegar—see Acetic acid, I. Oborgard.