The invention relates to a method of torrefaction of an optionally predried biomass in a torrefaction reactor such that torrefied biomass and torrefaction gases are obtained, and wherein an oxygen-containing gas is supplied to the torrefaction reactor at a first position in the reactor such that oxygen reacts with components of the torrefaction gases under the formation of heat and wherein torrefaction gases are withdrawn from the torrefaction reactor at a second position of the torrefaction reactor and wherein the first position is located downstream of the second position in relation to a biomass transport direction in the torrefaction reactor such that the torrefaction gases moves through the torrefaction reactor countercurrent with the biomass transport and wherein the optionally predried biomass has a temperature of between 30° C. and 230° C., preferably between 50° C. and 200° C., most preferably between 60° C. and 180° C. when entering the torrefaction rector.