In this work, thorough experimental characterization and theoretical investigation for the quantitative description of the breakage of needlelike crystals of βl-glutamic acid in a continuous rotor-stator wet mill are performed. The constitutive equations of the newly developed model rely on the physics of the phenomena occurring at the single crystal and at the process scale. The fundamental equations consider not only the operating conditions adopted for the grinding device but also the morphology of the crystals. First, a comprehensive experimental campaign is performed to investigate the effect of the different operating conditions, namely, the suspension density, the rotor speed, and the residence time in the grinding chamber, on the product properties, in particular, the average sizes and the particle size and shape distribution. Measurements are collected using an in-house developed double-camera stereoscopic measurement device, the μ-DISCO, capable of quantitatively measuring the particle size and ...