In metabolism, the dehydrogenating degradation of organic substance by organisms or cells under anaerobic conditions in which electrons are transferred to metabolites which accumulate and are excreted in reduced form. Fermentation is only possible if the organism is able to gain energy by this process.
In microbiology, the process in which cells (microorganisms, plant or animal cells) are cultured in a bioreactor in liquid or solid medium to convert organic substances into biomass (growth) or into products.
Source: PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 154 (https://doi.org/10.1351/pac199264010143)