A method for separating protein from plant or algae material is disclosed. The method comprises mixing the protein-containing material with a solvent, preferably water; extracting the protein-containing material at pH>7; and acidifying the mixture, thereby precipitating protein and fiber together. In some embodiments of the invention, the separation additionally comprises decanting the mixture to recover a protein/fiber solid; adding water to the protein/fiber solid; adding a predetermined quantity of base to the protein/fiber/water system, thereby precipitating fiber; separating the fiber from the protein in a decanter; and drying the protein solution. In other embodiments, the protein/fiber solid is processed directly, e.g. by being passed to an extruder. The use of the fiber as a carrier for the protein makes the inventive method more efficient than methods known in the art; in particular, the inventive method does not require the use of a high-g clarifier centrifuge.