Term for the biochemical metabolism of organic substances in the absence of oxygen. The fermentation of a wine usually takes place for the most part under anaerobic conditions. In 1861, the scientist Louis Pasteur (1822-1895) discovered in the course of his investigations that yeasts consume sugar much more quickly in an anaerobic environment. In this context, one speaks of the Crabtree effect. In contrast, the presence of oxygen is called aerobic.