This work presents a new procedure to determine the nucleation kinetics during the reactive precipitation of an organic substance. The new method has been applied to the pH-shift precipitation of L-glutamic acid upon mixing of an aqueous monosodium glutamate solution with hydrochloric acid. The induction time has been measured precisely in a stirred batch reactor by the combination of two in-situ measurement techniques, namely ATR-FTIR spectroscopy (attenuated total reflection Fourier Transform technique) and Focused Beam Reflectance Measurement (FBRM). It is shown that ATR-FTIR is a suitable tool to measure the concentrations of the different L-glutamic acid ions, and can be used to determine the starting time of the process when the desired supersaturation is established in the reactor. The onset of particle formation is detected through FBRM. The precipitated polymorph is identified using in-situ Raman spectroscopy and Particle Vision & Measurement (PVM). Finally, the induction time is used together with the independently measured growth kinetics to determine the nucleation rate.