A repeated impact test was used to determine the breakage behavior of granules containing an organic matetial which had a narrow size distribution of 600-700 mum and a moisture content (mass fraction) ranging from 0.02 to 0.32. In this test, a sample of approximately 200 granules encounters 100 particle-wall impacts per second with an adjustable impact velocity. The strength of the granules was thus determined by observing the breakage caused. Over the range of moisture contents tested, the granules have a maximum strength at a moisture content of between 0.20 and 0.25. From the amount of material sticking to the walls of the particle container, qualitative insight into the attrition strength of the granules is obtained. Using image analysis, the change of the particle size distribution and of the shape of the granules was determined. From these changes, appropriate breakage mechanisms are proposed: the breakage of granules with a high moisture content is mainly by attrition, while at low moisture contents, fracture of the granules into smaller pieces is the dominating mechanism.