Chemical and biochemical transformations during the industrial process of sherry vinegar aging.

The work described here concerns a study of the chemical and biochemical transformations in sherry vinegar during the different aging stages. The main factors that contribute to the nature and special characteristics of sherry vinegar are the raw sherry wine, the traditional process of acetic acid fermentation in butts (the solera system), and the physicochemical activity during the aging process in the solera system. A number of chemical and biochemical changes that occur during sherry vinegar aging are similar to those that take place in sherry wine during its biological activity process (where the wine types obtained are fino and manzanilla) or physicochemical activity process (to give oloroso wines). Significant increase in acetic acid levels was observed during the biological activity phase. In addition, the concentrations of tartaric, gluconic, succinic, and citric acids increased during the aging, as did levels of amino acids and acetoin. A color change was also produced during this stage. Glycerol was not consumed by acetic acid bacteria, and levels of higher alcohols decreased because of the synthesis of acetates. On the other hand, in the physicochemical phase the microbiological activity was lower. Concentrations of some cations increased because of evaporation of water through the wood. A color change was also produced in this stage. Concentrations of different amino acids decreased because of reaction with carbonyl compounds. A precipitation of potassium with tartaric acid was also observed.