Abstract: A tiltable fermentor includes a hollow perforated drum rotating within a generally cylindrical jacketed pressure vessel. The drum is cantilever-mounted and supported at one driven end by a shaft for rotation which is indirectly motor driven by means of an adjustable pulley and belt. The other end of the drum has no central bearing but is circumferentially supported by bearing strips affixed to the inner surface of the outer pressure vessel. A hinged headplate on the pressure vessel, swings open to expose the open undriven end of the inner drum, thereby facilitating loading and unloading. The entire fermentor assembly, that is, vessel, drum and drive, is pivotably mounted so that the rotational axis of the drum may be horizontal or tilted about a transverse axis to a 45 degree angle, with the hinged headplate being either up or down. The drum can rotate at any orientation, and the absence of a drum bearing at the undriven end permits rotational operation even when the headplate is swung open.