Dynamic monitoring of glycine crystallisation with low power ultrasound reflection spectroscopy

•A improved ultrasound technique is shown to accurately monitor crystallisation.•The optical cloud point can be determined using ultrasound with high accuracy.•Results agree closely with standard optical turbidity.•The ultrasound technique may be detecting scattering bodies in the metastable zone.•The technique may give more information than optical techniques and be used to study structures. Crystallisation processes are ubiquitous in the food and pharmaceutical industries and the development of process analytical technologies (PAT) for on-line, in situ monitoring is essential to ensure process efficiency and to optimise product quality. Current PAT, many of which are based on electromagnetic waves, have a range of limitations including an inability to accurately measure opaque solutions. Low power (