Disclosed is a method for the continuous hydrothermal pretreatment of a lignocellulosic biomass feedstock selected from cereal straw, wheat straw, corn stover or bagasse, comprising the steps of: (i) soaking (such as in the presence of an acetic acid containing liquid from a subsequent step of the hydrothermal pretreatment) so as to drive out air from the feedstock and to ensure that all the feedstock is saturated with liquid； (ii) continuous pressurised hydrothermal pretreatment at temperatures of between 170 and 200° C (conducted with or without addition of acids, bases or other chemicals)； (iii) pressing the pretreated feedstock while it is still under pressure or after it has been unloaded from the pretreatment reactor to create a fibre fraction and a liquid fraction； and (iv) subjecting the fibre fraction to enzymatic saccharification (such as a simultaneous saccharification and fermentation (SSF) process to produce ethanol)； and wherein the temperature and residence time for the hydrothermal pretreatment step are selected such that greater than 80% of the original lignin content of the feedstock prior to pretreatment remains in the fibre fraction.
