The strength and breakage mechanisms of detergent enzyme granules and typical core materials used for enzyme granules (all of size 500-600 mum) have been investigated under impact and shear stress conditions to simulate the stresses experienced in a detergent factory. In an Impact Tester, single-particle experiments were performed at impact velocities of 8-25 m/s. Multiple (bulk) particle experiments were performed in an Attrition Shear Cell (ASC), where the particles were exposed to shear strains of about 1250 and normal stresses of 1-30 kPa. For coated enzyme granules the results indicate that the primary breakage mechanism after repeated impacts at 10 m/s is chipping associated with local delamination. Damages to the coating layer may expose the underlying enzyme-containing layer or core and lead to the release of enzyme-active dust. Markedly lower enzyme dust release was obtained by incorporating the enzyme into the core of the granule as compared to a layer-structured enzyme distribution. Furthermore, the results indicated that stronger enzyme granule core materials provide a better impact resistance of the final enzyme granule towards the release of enzyme-active dust. Coating layers of inorganic salts and water-soluble polymers are observed to enhance the breakage resistance of the enzyme granules tremendously. The impact and shear resistance of four different placebo enzyme granule core particles were investigated. A transition from chipping to fragmentation as the main breakage mechanism was observed at impact velocities from 8 to 20 m/s. Experiments performed with attrition shearing indicated that the extent of breakage depend on surface friction and particle sphericity as well as intraparticular forces. The results obtained in this work are of importance for the design and formulation of mechanically resistant enzyme granules. (C) 2004 Elsevier B.V. All rights reserved.