The quality of biomass powders depends on the size reduction technology used to produce them. Attritional mills (e.g. hammer mills) require biomass that is chipped and pre-dried. These processes degrade the green chemical profile of biomass and complicate handling and storage. A multi-blade shaft mill (MBSM) produces fine powders in a single step from green biomass. This enhances utilisation in downstream biorefining processes. Investigations have evaluated the powder quality and the energy requirements of MBSM milling using pinewood at a range of moisture contents. The shape and size properties of powders were analysed using two-dimensional image analysis and surface features investigated by scanning electron microscopy. A higher fraction (55 to 80 %) of finer powders (< 0.5 mm) was observed through multi-blade milling in comparison to hammer milling (41 %). There were also significant differences in particle (MBSM powders produced from green logs) aspect ratios (0.54 to 0.58 vs. 0.36 to 0.43) and specific surface (33 to 56 mm-1 vs. 29 to 38 mm-1). The MBSM specific milling energy ranged from 99 to 232 kWh tâ1 (dry mass (DM)). These results are promising for the conversion of biomass powders into value added products (e.g. bio-based chemicals and nanocellulose) and indicate that MBSM technology may have a niche application in biorefining.