An experimental study was carried out to determine the effect of compaction on arching of wheat flour in storage. A model bin 475 mm in height and 600 x 375 mm in cross-section was used to conduct tests and wheat flour at moisture contents (MC) of 8.6% and 14.2% was tested. Direct shear tests were performed to determine the angle of internal friction and cohesion of wheat flour subjected to various compaction pressures. It was observed that the internal friction angles were about the same for the wheat Hour at two moisture contents (37.6 degrees vs. 37.5 degrees), but cohesion for 14.2% MC was 72% higher than that for 8.6% MC. The flowability of wheat flour decreased with increasing compaction pressure sharply at the initial stage of compaction. Compaction led to a 64% increase in required hopper opening for arching-free flow for flour at 8.6% MC, and 49% at 14.2% MC. However, compaction pressure had little effect on arch formation after it reached above 5 kPa. (C) 2009 Elsevier Ltd. All rights reserved.