The invention relates to a method for impregnating biomass (10). In a step (S100) of the method, a reactor unit (11) is fed with biomass (10) by means of a plug screw (12). In another step (S200), the reactor unit (11) is at least partially filled up to a predetermined fill level (13) with a reactant (18), such that a reaction between the fed biomass (10) and the reactant (18) takes place in order to obtain an impregnated biomass. In another step (S300), the impregnated biomass (10) is discharged from the reactor unit (11) for further processing (S300). The invention further relates to a device (1) for impregnating biomass (10).