1) anaerobic digestion 2) anaerobic fermentation the digestion of materials from biological sources in the absence of air GRM: n. (1,2) Note: the following anaerobic fermentation processes are significant in obtaining useful forms of energy from biomass: alcoholic fermentation, fermentation processes whereby certain microorganisms extract energy from glucose and other substrates, with alcohol as an end product; methane fermentation, generally termed anaerobic digestion, fermentation processes whereby organic acids produced by certain micro-organisms are converted by other micro-organisms to methane and carbon dioxide so produced is known as biogas References: GENfermentation