600053 Disclosed is a method of filtering a liquid protein mixture, the method comprising: providing a liquid mixture at a first pressure (P1), the liquid mixture comprising a carrier liquid, a protein at a first concentration (C1) relative to the carrier liquid and a dispersed contaminant； passing the liquid mixture through a filter to form a filtrate at a second pressure (P2), the filtrate comprising the carrier liquid and the protein at a second concentration (C2) relative to the carrier liquid, wherein the filter is sized to remove at least a portion of the dispersed contaminant from the liquid mixture； and applying a counter pressure to the filtrate to ensure that a pressure differential between the first and second pressures (P1 - P2) is not more than about 300 mbar. Further disclosed is a method of filtering a liquid protein mixture, the method comprising: providing a liquid mixture at a first pressure (P1), the liquid mixture comprising a carrier liquid, a protein at a first concentration (C1) relative to the carrier liquid, and a dispersed contaminant； passing the liquid mixture through a filter to form a filtrate at a second pressure (P2), the filtrate comprising the carrier liquid and the protein at a second concentration (C2) relative to the carrier liquid, wherein the filter is sized to remove at least a portion of the dispersed contaminant from the liquid mixture； and applying a counter pressure to the filtrate sufficient to yield an average filtrate flow rate of at least about 300 g/min.m2 of filter surface area. Further disclosed is a method of filtering an aqueous protein mixture, the method comprising: providing an aqueous mixture at a first pressure (P1), the aqueous mixture comprising water and von Willebrand factor (vWF) at a first concentration (C1) relative to the water； passing the aqueous mixture through a porous membrane filter to form a filtrate at a second pressure (P2), the filtrate comprising the water and the vWF at a second concentrat
