The invention relates to a bioreactor for methanizing biomass, a biogas plant having a plurality of such bioreactors, and a method for operating such a bioreactor. Because the elongated reactor vessel includes both a loading gate and an unloading gate that are arranged at opposite ends of the elongated reactor vessel, it is possible to remove consumed biomass, which is harmless in terms of epidemiologic hygiene and plant hygiene due to thermophilic process control during the fermentation, from the reactor vessel through the unloading gate and to transfer this consumed biomass directly to the composting process. The bioreactor thus has a “clean” unloading gate and an “unclean” loading gate.
