A method is disclosed for filtering a protein in a liquid mixture in a manner that does not substantially damage or otherwise limit the recovery of the protein in the filtration filtrate. The method generally includes passing a liquid mixture containing a protein (e.g., an aqueous vWF mixture) through a filter while applying a counter pressure to the liquid mixture filtrate to accurately reduce and control the pressure differential across the filter. The disclosed method has the advantage that relatively high filtration flow rates can be achieved at relatively low pressure differentials, in contrast to high pressure differentials, which actually reduce the filtration flow rate of protein liquid mixtures. Further, the method can recover substantially all of the protein that is initially present in the liquid mixture.
