Closed-loop computer control of solution supersaturation based on in-process measurements of the concentration using ATR-FTIR spectroscopy and adaptive determination of the corresponding temperature profile has been applied to control the crystallization of monosodium glutamate from an aqueous solution. The crystal size and its distribution are varied and optimized by applying different control strategies such as rapid desupersaturation, constant supersaturation, and step-changing supersaturation profiles.