Abstract: It includes the stages of grinding the lignocellulosic biomass to a size of 15-30 mm, subjecting the product obtained to steam explosion pre-treatment at a temperature of 190-230° C. for between 1 and 10 minutes in a reactor (2), collecting the pre-treated material in a cyclone (3) and separating the liquid and solid fractions by filtration in a filter press (9), introducing the solid fraction in a fermentation deposit (10), adding a cellulase at a concentration of 15 UFP per gram of cellulose and 12.6 International Units of ?-glucosidase enzyme dissolved in citrate buffer pH 4.8, inoculating the fermentation deposit (10) with a culture of the heat-tolerant bacteria Kluyveromyces marxianus CECT 10875, obtained by chemical mutagenesis from strain DER-26 of Kluyveromyces marxianus and shaking the mixture for 72 hours at 42° C.