Flow and shear descriptors of preconsolidated food powders

This study proposes a friction based index to characterize food powder strength during flow and shear. It is shown that the peak strength of powders observed in direct shear tests consists of interlocking and intrinsic value of friction between particles. These components were determined separately using the energy input and dissipation characteristics of powders during shearing. Friction value was determined on commercial powdered salt, sugar, cocoa, and cheese and compared to different bulk and flow properties such as angle of repose, cohesion, angle of internal friction, and unconfined yield stress. Measurements of friction values showed better repeatability than the angle of repose technique, commonly used in the food industry for flowability determination. Lower angles of internal friction found in cohesive cocoa and cheese powders agreed with lower friction values obtained for these powders. This indicated the prevalence of interlocking and frictional forces at peak failure in comparison to adhesive and other attraction forces of lower magnitude.