Dry mixing of wheat flours: Effect of particle properties and blending ratio

A study was undertaken to evaluate the effects of physical and morphologica l characteristics of soft and hard wheat flours on dry mixing. Two soft whe at flours with different particle size ranges (< 38 mum and > 38 mum SWF) w ere mixed with each of three hard wheat flours with different particle size ranges (< 38 mum, 38-75 mum, and > 75 mum HWF) at three ratios (20 : 80, 5 0 : 50 and 80 : 20, w : w) in a laboratory drum mixes. At set intervals, mi xtures were sampled from 10 points in the mixer to measure the degree of mi xing. The shape and surface of flour particles were examined with a scannin g electron microscopy. Flour mixing in a double ribbon mixer also was inves tigated in the same manner. In both mixing studies, the mixture containing smaller, smoother, more spherical, flour particles achieved a higher degree of uniformity (p < 0.05) and required longer mixing time than the mixture containing bigger, rougher, more irregular, flour particles. The mixing rat io of SWF : HWF 50 : 50 (w : w) required a significantly longer mixing time than the mixing ratio of SWF : HWF 80 : 20 (w : w). The dry mixing of both soft and hard wheat flours was well explained by the exponential decay mod el. The mixing mechanism for both mixers were identified, and a predictive integrated model for mixture uniformity was developed.