Increasing teff (Eragrostis tef) consumption has been recorded in recent years due to its gluten-free nature and exceptional nutritional composition. Studies on the particle level that relates to processing and handling of teff flour are limited. The effect of different milling methods (roller mill, pin mill, and hammer mill) on size distribution, shape characteristics, and flowability of teff flour was evaluated. Physical properties (angle of repose, tapped and bulk densities, size distribution, and shape characteristics) and proximate composition were investigated and correlated with flow properties. Flowability was measured in terms of bulk, shear, and dynamic flow properties using the FT4 powder rheometer. Particle size distribution significantly (p < .05) influenced the angle of repose, aeration energy, and wall friction angle while shape characteristics (circularity and aspect ratio) significantly (p < .05) affected the aerated and tapped bulk densities and basic flow energy. Hammer-milled flour had the highest aerated (548.00 kg/m3 ) and tapped bulk densities (804.33 kg/m3 ). Pin-milled flour had the highest compressibility index (38.46%), Hausner ratio (1.62), angle of repose (71.57°), and wall friction angle (25.92° at 3 kPa) indicating poorer flowability. Stability index and specific energy did not vary significantly (p > .05) among the milled flours. Highest basic flow (1,191.03 mJ) and aerated energies (272.32 mJ) were required to induce flow in hammer-milled flour due to greater proportion of large particles. Based on the flow function, all flours fall under the "easy flowing" category, but the pin-milled flour exhibited the poorest flowability.
Keywords: density; flow property; milling; particle shape; particle size; teff flour.
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