A pyrolysis plant 20 comprises a grinding pyrolyser 22, being a machine or apparatus in which both particle size reduction and pyrolysis occur simultaneously. Plant 20 also comprises a bin (hopper) 30 for holding wet particulate biomass feedstock. Chute 32 leads from the bin 30 to a biomass dryer 34 which reduces moisture content of the feedstock as low as possible, e.g., to below about 10. Dried feedstock is conveyed from dryer 34 via line 36 to a dried biomass feedstock hopper 38. Dried feedstock is fed from hopper 38 into a chute 40 which leads to an inlet trunnion 42 of grinding pyrolyser 22. A discharge trunnion 44 of grinding pyrolyser 22 leads to a char holder 60 for collecting char particles and a condensation train 62 for condensing vapour generated by the pyrolysis to produce oil.