NOVELTY - Biochemical production of biofuel from lignocellulosic biomass by enzymatic hydrolysis of cellulose in biomass and fermentation of sugars obtained, involves: a) heating biomass with steam to preselected temperature/pressure/time to obtain dissolved hemicellulose breakdown products and solids fraction; b) explosively decomposing biomass by rapidly releasing pressure to break down biomass into reaction mixture containing fibers; c) removing liquid fraction from reaction mixture, before/after explosive decomposition; and d) liquid extracting solids fraction, before/after decomposition.    USE - For the biochemical production of biofuel from lignocellulosic biomass by enzymatic hydrolysis of cellulose in the biomass and fermentation of the sugars obtained from it (claimed); or for the production of ethanol from biomass. The lignocellulosic biomass includes: wood residues (sawdust, bark or other); municipal paper waste; agricultural residues (including corn stover, corncobs and sugarcane bagasse); and dedicated energy crops (composed of fast growing tall, woody grasses such as switchgrass and miscanthus).    ADVANTAGE - The method reduces the inhibitory impact of breakdown products and other inhibitory compounds produced or released during the pretreatment of lignocellulosic biomass; provides an improved lignocellulosic biomass pretreatment step for a biofuel production where hemicellulose, hemicellulose degradation and hydrolysis products, cellulose degradation products and other inhibitory compounds typically present in biomass such as fatty acids, sterols, esters, and ethers are removed in a commercially viable, economical manner prior to the enzymatic hydrolysis step to achieve the most economical maximization of hydrolysis and fermentation yields; and improves the overall ethanol yield by successfully reducing the amount of inhibitory compounds in the pretreated biomass are generally linked to increased cost for operating the respective method, thus increased yields are only obtainable at significantly increased costs which are higher overall than the value of the increased ethanol yield or decreased hydrolysis or fermentation times and reduced enzyme costs, rendering existing methods economically unacceptable. Therefore, the removal of inhibitory compounds improves the economics of the process by reducing enzyme load and improving enzyme efficiency and fermentation performance.    DETAILED DESCRIPTION - Biochemical production of biofuel from lignocellulosic biomass by enzymatic hydrolysis of cellulose in the biomass and fermentation of the sugars obtained, the improvement comprising a pretreatment process involves: a) heating the lignocellulosic biomass with steam to a preselected temperature, at a preselected pressure and for a preselected time to hydrolyze and solubilize hemicelluloses in the lignocellulosic biomass and obtain a liquid fraction including dissolved hemicellulose breakdown products and a solids fraction; b) explosively decomposing the lignocellulosic biomass by rapidly releasing the pressure to break down the lignocellulosic biomass into a reaction mixture containing fibers; c) removing the liquid fraction from the reaction mixture, before or after the explosive decomposition, for removing dissolved compounds which are inhibitory to enzymatic cellulose hydrolysis; and d) liquid extracting the solids fraction, before or after explosive decomposition, for removing from the solids fraction soluble compounds which are inhibitory to enzymatic cellulose hydrolysis, where, for maximizing the overall economy of the biofuel production process by optimizing an amount of eluent used in the extracting step, the liquid extracting step is discontinued once a content of hemicellulose, xylo-oligosaccharides and xylose in the solids fraction, measured as a xylose equivalent content, has reached a level of 4-8 wt.% of the dry matter of the solids portion.