Abstract: The present invention provides a method for extracting polymeric pentose, preferably xylan, from a polymeric pentose containing liquid/slurry, preferably black liquor, comprising the following steps: a) providing a polymeric pentose containing liquid/slurry; b) concentrating the polymeric pentose by membrane separation of a said polymeric pentose containing liquid/slurry; and c) adding alcohol to the concentrate obtained in step b) and subsequently acidifying said concentrate obtained in step b) for precipitating polymeric pentose whereby a polymeric pentose product, or an intermediate polymeric pentose product, is obtained. In this above way polymeric pentose, e.g. xylan, is separated whereby the use of methanol (less lignin must be kept in solution) and acid (less acid which buffers the pH-decrease) become much lower.