Agricultural wastes are increasingly being used as biomass materials for co-firing in coal fired power stations. However issues in milling and conveyance of agricultural residues are limiting the use of these resources and a greater understanding of their milling and conveyance behaviours is required to overcome the issues being seen in industry. The batch milling process of a planetary ball mill can be used to simulate various conditions within a continuous flow ball mill, which allows for the analysis of the different of mill variables, and identify the optimal milling conditions within the mill for different biomasses. For this study, as received olive cake was milled in a laboratory scale planetary ball mill for a range of mill variables in order to ascertain the impact of these variables on milling behavior. The variables investigated were volume (100-200ml), mill rotational speed (200-600 RPM), and energy inputs/time (0.1 kJ-8 kJ). During the milling process caking was observed for all speeds and volumes, especially for long milling periods and was more pronounced for higher speeds. Dusting was observed for high volumes at low speeds for prolonged milling durations. The impact of overloading the mill can be seen by the increased energy requirements and milling times; low speeds result in incomplete milling and dusting, and high speeds result in extreme caking in short time periods.