The nucleation control and separation of the metastable alpha-L-glutamic acid polymorph from aqueous solution was successfully carried out in the presence of the selective additive I.-tyrosine. The influence of different additive concentrations on the solubility, pH and nucleation time of L-glutamic acid polymorphs was revealed. It is found that below a critical level of concentration ( < 0.07 g/100 ml), the incorporated additive suppresses the nucleation of the commonly occurring stable beta-polymorph effectively and promotes the nucleation of rarely occurring metastable alpha polymorph. Above the critical level, the additive suppresses completely the nucleation of both alpha- and beta-polymorphs in the solution. For the first time, a bulk single crystal measuring size of 20 x 11 x 8 mm(3) of the metastable alpha-L-glutamic acid was successfully grown from aqueous solution in the presence of an optimized concentration of I.-tyrosine by the slow cooling method with the reversible seed rotation technique. Morphology of the grown crystals was revealed in accordance with equilibrium morphology. X-ray powder diffraction and single crystal structural refinement studies reveal that the incorporated additive molecules do not alter or enter into the crystal lattices but plays their inhibitory role only by just making their presence in the solution. (C) 2012 Elsevier B.V. All rights reserved.