A method of reducing the level of RNA in a biomass comprising filamentous fungus comprises: (i) heating the biomass, downstream of the fermenter to a first temperature and (ii) separating said biomass comprising filamentous fungus from other components. The fluid removed in step (ii) may be recirculated to a heat exchanger, which is used to heat the biomass in step (i). Also disclosed is a biomass per se, said biomass comprising a filamentous fungus isolated from a biomass and liquid mixture, the liquid comprising particles of filamentous fungus with one or more of the following characteristics: a median size of less than 1.3 µm, a mean size of less than 1.4 µm, a mode size of less than 1.4 µm, a D (v, 0.1) of less than 0.85 µm, a D (v, 0.5) of less than 1.20 µm, a D (v, 0.9) of less than 1.5 µm. The advantage is a more efficient process of reducing the RNA content of the biomass.
