NOVELTY - Hemicellulose removal is carried out during a cooking phase in which the release of hemicellulose into the cooking liquor from the lignocellulosic material is at or close to the maximum and the released hemicellulose is in a polymeric state.    USE - The recovered hemicellulose contains galactoglucomannan, which can be cleaved to form galactose, glucose and mannose, which can then be fermented to produce ethanol for e.g. vehicle fuel or as a petrochemical product substitute. Galactoglucomannan can also be used to prepare hydrogels used for coating seeds and other agricultural applications, for medical applications (e.g. as slimming aids) or for preparing barrier films for foodstuff packaging.    ADVANTAGE - Large quantities of hemicellulose, especially galactoglucomannan, can be recovered, providing a cheap and readily available raw material for the production of ethanol by fermentation. The removal of hemicellulose also improves the quality of the pulp, reducing bleaching chemical consumption and reducing the load on the soda furnace.    DETAILED DESCRIPTION - A method for recovering hemicellulose during cooking of lignocellulosic material using an acidic, neutral or weakly alkaline cooking liquor in order to produce chemical or chemimechanical pulp, comprises removing some of the cooking liquor and subjecting it to ultrafiltration (22) or reverse osmosis in order to remove at least a considerable proportion of the hemicellulose. The treated liquid is then preferably returned to the cooking step (1-3). Hemicellulose removal is carried out during a cooking phase in which the release of hemicellulose into the cooking liquor from the lignocellulosic material is at or close to the maximum and the released hemicellulose is in a (predominantly) polymeric state.    DESCRIPTION OF DRAWING(S) - The figure shows a batch digester in a sulfite pulp mill.    digesters (1-3)    cooking liquor collection tank (20)    ultrafiltration device (22)    buffer tank for permeate (25)    outlet pipe for hemicellulose concentrate (26)