Abstract During the methanogenic fermentation of cassava peel, its composition (high starch content, high carbon: nitrogen ratio, presence of cyanogenic glucosides) usually results in excess acid production, nitrogen deficiency and the release of cyanide, which is highly toxic to methanogenic bacteria. The utilization of a plug flow digester (‘Transpaille’) solved the problem of acidification through localization of the acidogenic phase in the first half of the fermenter and the problem of nitrogen deficiency because a permanent liquid phase allowed nitrogen accumulation. No perturbation due to cyanide (5–6 mg/l) was observed in the fermenter. A fermentation yield of 0·661 m 3 biogas/kg volatile solids (VS) was obtained with a loading rate of 3·6 kg VS/m 3 day. Energy-saving calculations showed that a fermenter of 88 m 3 is needed to produce the methane necessary for drying one ton of cassava meal.