Process for the treatment of a feedstock containing biomass, the process including a) drying the feedstock at a temperature between 20 and 180° C. for a duration between 5 and 180 minutes, b) torrefaction of the feedstock originating from step a) in order to produce at least one torrefied biomass solid effluent, c) co-grinding the torrefied biomass solid effluent originating from step b), in the presence of at least one solid fossil feedstock in order to obtain a powder.