The invention relates to a method and a device with the aid of which hydrogen halide and water are removed from biomass hydrolyzates containing halogen acid. The core of the invention is an evacuated container (B1), which is continuously supplied with a heat-transfer medium and which is completely filled with the heat-transfer medium in a part. In said evaporation chamber, the biomass hydrolyzate is likewise continuously introduced. In the container (B1), heat is transferred from the heat-transfer medium to the hydrolyzate, wherein hydrogen halide and water are continuously evaporated. The remaining hydrolyzate particles are continuously discharged with the cooled heat-transfer medium and continuously removed by means of the heat-transfer medium and continuously separated from said heat-transfer medium. The invention described can also be used to treat other mixtures or solutions for the purpose of evaporation. The following is fundamental in regard to the heat-transfer medium used: the heat-transfer medium is chemically inert with respect to the introduced substances.