The present disclosure provides a method for pre-treating non-wood lignocellulosic material containing less than 5 % (w/w) starch or sugar in a process for production of ethanol from lignocellulose, comprising the steps of: adding organic acid or organic acid-producing bacteria to the lignocellulosic material; storing the lignocellulosic material in the presence of the organic acid for a period of at least two weeks in an atmosphere of less than 5% oxygen to obtain organic acid-impregnated material; and heating the organic acid-impregnated material at a temperature of at least 160° C. to obtain pre-treated lignocellulosic material, wherein no, or substantially no, inorganic acid or base, including SO2, is added in the method.