A reactor for drying and torrefaction, configured for torrefying biomass, including a chamber in which two separate areas are delimited, a mechanism for mixing and transferring biomass from one end of the chamber to the other, a drying device in an upstream area of the chamber configured to dry the biomass introduced into the reactor, a torrefaction device in a downstream area of the chamber configured to torrefy biomass dried in the upstream area, and a transfer and sealing system configured to allow dried biomass to be transferred from the upstream area to the downstream area at time intervals, and to make the two areas mutually sealed during each interval. Such a reactor may, for example, find application to torrefaction of lignocellulosic biomass.