This short communication investigates the impact of impurity on crystal growth behaviour in terms of crystal shape distribution. A two dimensional population balance model is applied to study the crystal shape changing behaviour in cooling crystallisation producing beta-form L-glutamic acid crystals, in the presence and without the presence of an additive, L-phenylalanine. The simulation results were verified in experiments using a 1-litre crystalliser for crystallisation of L-glutamic acid. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.