A method of reducing the level of RNA in a biomass comprising filamentous fungus involves the following steps: (i) heating the biomass, downstream of the fermenter to a first temperature in the range 40-69℃； (ii) heating the biomass to a second temperature which is 6-20℃ greater than the first temperature, to facilitate release of RNA from cells of the filamentous fungus； and (iii)separating filamentous fungus having a reduced level of RNA from other components.The fluid removed in step (iii) may be recirculated to a heat exchanger, which is used to heat the biomass in step (i).一種減少包含絲狀真菌的生物質中之RNA含量的方法涉及以下步驟：(i)在發酵槽的下游加熱所述生物質至40-69℃範圍內的第一溫度；(ii)加熱所述生物質至高於所述第一溫度6-20℃的第二溫度，以利RNA從絲狀真菌細胞中釋放；及(iii)從其他組分分離具有減少的RNA含量之絲狀真菌。在步驟(iii)中移除的流體可再循環至熱交換器，其係用於加熱步驟(i)中的生物質。
