A device (1) and a method for carrying out a fermentation process in a reactor (2), which reactor (2) comprises a liquid-permeable floor (3), two substantially parallel side walls (4) extending perpendicularly to the floor (3), a rear wall (13), and a ceiling part (5) disposed opposite the floor (3), which joins said side walls (4) and said rear wall (13), which device (1) further comprises a pipe (6) for discharging liquid from the reactor (2), which pipe (6) is disposed underneath the floor (3), and which device (1) further comprises means (7) for moisturising the material to be fermented that is present in the reactor (2) as well as means (8) for providing access to the reactor (2) for the purpose of supplying and discharging material (9) to be fermented and fermented material (9), respectively, and which device (1) furthermore comprises a pipe (14) for discharging biogas from the reactor (2).