Provided are new methods for precipitating proteins comprising (a) providing a protein solution, (b) adding a salt to the solution, (c) either (i) adjusting pH of the composition to below the pI of the protein (in cases where the method is directed towards precipitation of most or all proteins in the solution) or (ii) adjusting the pH of the composition to above the pI of the protein (in cases where keeping the target protein in solution is desired), and (d) adding an organic compound to the solution, wherein (I) in the case where the method comprises step (c)(i) a two phase solution is formed wherein at least about 75% of the protein is contained in the protein phase or (II) in the case where the method comprises step (c)(ii) the method further comprises removing precipitated impurities from the protein solution.
