2 to 4 hours are required for the second stage of the process according to the invention when working under pressure a pressure of up to 4 atmospheres gauge in particular 1 3 atmospheres gauge is used preferentially and the temperature is preferably 125 u00b0 135 u00b0 c the acid concentration is preferably 0 2 0 6 by weight hcl or hbr or 0 2 0 6 by volume of h 2 so 4 and the ratio of liquid to solid should preferably be from 4 1 to 7 1 volumes weight of solids the time required is approximately 1 2 hours after completion of the second stage of the process the batch is filtered the liquid can be processed to give xylose or directly to give xylitol if sulphuric acid has been used in the second stage the mixture can be neutralized with calcium oxide calcium carbonate or preferably barium carbonate in the calculated amount in that case after removing the precipitate a xylose solution which can be reduced directly to xylitol is obtained while hitherto it has been necessary to concentrate the solution or pass it over ion exchangers to remove acetic acid the yield of pure xylose is up to 25 and further proportions of xylose namely up to 10 can be isolated from the mother liquor the process according to the invention results in splitting of the bonds of the lignin to the polysaccharides in the oat husks without the lignin undergoing a further polymerization as is the case in the known hydrolysis processes the lignin can easily be dissolved out of the filtration residue from the second stage of the process according to the invention by washing with an organic solvent such as methanol or.