Monitoring of fat crystallization process using UVP–PD technique

The dynamic response of the cocoa butter shear crystallization process to a step reduction in temperature of a two stage shear crystallizer is investigated by measuring the pulsed ultrasound Doppler based velocity profile (UVP) and pressure drop (PD) in a pipe section. In addition, the velocity of sound, attenuated amplitude of the transmitted signal and temperature are continuously recorded. The temporal variation in rheological properties such as the apparent viscosity at different shear rates and the corresponding radial position in the pipe are determined by fitting the velocity profile and pressure drop to the power law rheological model. The linear dependence of sound velocity on the solid fat content (SFC) in the cocoa butter crystal suspension previously determined using the nuclear magnetic resonance technique is used to characterize crystallization. The cocoa butter crystal suspension is found to be shear thinning, the value of the power law exponent decreasing with increase in SFC. Newly developed software is used to integrate on-line measurement of flow profiles, pressure difference, temperature, velocity of sound and the attenuated amplitude of the transmitted signal. The software also calculates velocity profiles using spectral signal analysis, determines the rheological properties, and provides a graphical user interface and tools for data visualization. It is demonstrated that the cocoa butter shear crystallization process can be monitored using the UVP–PD technique.