Abstract: A method for separating and recovering compounds from biomass is provided. In the method, an aqueous extraction fluid in essentially gaseous phase, such as steam, is propagated through a reaction area containing biomass feedstock. When extraction fluid advances through the biomass feedstock, in predetermined reaction conditions, a target compound separates from the essentially solid feedstock matter and travels, with the extraction fluid, towards the end of the reaction area, in where the target compound is recovered in the form of an essentially liquid medium. The method is beneficial for extracting long-chain hemicelluloses from cellulose-containing feedstocks.

Abstract: Method of treating a biomass containing a fibrous structure and polysaccharides. According to the method the biomass is subjected to extractive treatment at which it is heated in aqueous phase at an absolute pressure of over 0.6 MPa and a temperature of at least 160° C. for separating polysaccharides from the mass. According to the invention, the pH of the biomass which is subjected to the extractive treatment is not actively lowered during the extraction and after the treatment the pressure is controllably reduced so as not to decompose the fibrous structure of the biomass. The polysaccharides separated from the mass are recovered as a first fraction, the fibrous structure of the biomass as a second fraction and at least one of the fractions is subjected to further processing. By means of the invention it is possible to isolate from the starting materials valuable compounds and groups of compounds by a method suitable for use on an industrial scale.