A filtration method involving a filtration device having a process tank, into which at least one feed for supplying a medium to be processed, in the form of a fermentation broth to be filtered, empties, wherein at least one filtration arrangement is arranged in the process tank and wherein the process tank has at least one drain and is designed in such a way that the filtration of the medium to be filtered can be carried out with the retentate remaining in the process tank until the retentate is released after completion of filtration, having the following method steps: a) the process tank is filled with the medium to be filtered and a pre-defined transmembrane pressure is produced at the at least one membrane filtration arrangement; b) the medium in the form of fermentation broth in the process tank is filtered by means of the membrane filtration arrangements until a pre-defined limit value for the mass fraction of solid material, in particular the biomass fraction, is reached, characterized in that c) the medium in the form of fermentation broth in the process tank is filtered in step b) by means of the filtration arrangements while simultaneously replenishing the volume of liquid flowing off as permeate by additional medium flowing in until a pre-defined limit value for the mass fraction of solid material, in particular the biomass fraction, is reached, wherein d) the transmembrane pressure during filtration is held constant and e) the medium in the form of fermentation broth in the process tank from step b) is subjected to further filtering by means of a wash-type diafiltration, with the replenishing flow of fermentation broth that has occurred up to this point being stopped and outflowing permeate being replaced by an addition of washing liquid to the tank, f) the residual liquid is then released from the process tank, and g) the process tank is cleaned, wherein the filtration step or steps is or are performed with at least one or more of the following filtration arrangements: the filtration arrangement has at least one, two or more hollow shafts, on each of which a plurality of membrane filter disks is arranged, the at least one or more hollow shafts being assigned at least one drive, and permeate being discharged from the process tank through the hollow shafts, and wherein the transmembrane pressure at the membrane filter disks is produced by pressurization with a gas and by a liquid column above the membrane filter disks, wherein a falling level in the course of concentration and a corresponding change in the hydrostatic pressure are compensated by the application of gas pressure. a) the process tank is filled with the medium to be filtered and a pre-defined transmembrane pressure is produced at the at least one membrane filtration arrangement; b) the medium in the form of fermentation broth in the process tank is filtered by means of the membrane filtration arrangements until a pre-defined limit value for the mass fraction of solid material, in particular the biomass fraction, is reached, characterized in that c) the medium in the form of fermentation broth in the process tank is filtered in step b) by means of the filtration arrangements while simultaneously replenishing the volume of liquid flowing off as permeate by additional medium flowing in until a pre-defined limit value for the mass fraction of solid material, in particular the biomass fraction, is reached, wherein d) the transmembrane pressure during filtration is held constant and e) the medium in the form of fermentation broth in the process tank from step b) is subjected to further filtering by means of a wash-type diafiltration, with the replenishing flow of fermentation broth that has occurred up to this point being stopped and outflowing permeate being replaced by an addition of washing liquid to the tank, f) the residual liquid is then released from the process tank, and g) the process tank is cleaned,