TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: The pretreatment process involves contacting the cellulosic biomass with at least one aqueous pretreatment fluid to obtain pretreated cellulosic biomass, or performing steam explosion or advanced steam explosion. The advanced steam explosion process involves pretreating the cellulosic biomass in a first pressurized reactor, where the cellulosic biomass undergoes hydrolysis in the first pressurized reactor, discharging the cellulosic biomass from the first pressurized reactor to pressurized sealing device having a first pressurized coupling to cellulosic biomass discharge port of the first pressurized reactor, maintaining vapor phase in the first pressurized reactor by injecting steam into the first pressurized reactor, where the injected steam provides heat energy to the cellulosic biomass in the first pressurized reactor, washing the cellulosic biomass in downstream region of the first pressurized reactor or the pressurized sealing device, draining liquid including dissolved hemicellulosic material extracted from the cellulosic biomass from at least one of the first pressurized reactor and the pressurized sealing device, discharging the cellulosic biomass from the pressurized sealing device through a second pressurized coupling to a second pressurized reactor, where the cellulosic biomass is maintained at a higher pressure in the second pressurized reactor than in the first pressurized reactor, infusing cells of the cellulosic biomass with steam or water vapor by injecting steam or water vapor into the second pressurized reactor, and rapidly releasing pressure applied to the cellulosic biomass infused with water to cause steam expansion in cells of the cellulosic biomass and refine the cellulosic biomass to obtain the pretreated cellulosic biomass. The method further involves fermenting the fermentable sugar in fermentation process utilizing at least one microorganism. The microorganism is chosen from wild-type bacteria, recombinant bacteria, wild-type filamentous fungi, recombinant filamentous fungi, wild-type yeast, recombinant yeast and their combinations. The pretreated cellulosic biomass has solid concentration of 10-35 weight/weight%. The starting pH is 5.7-6.1. The step (d) is performed for 50-200 hours. EXAMPLE - No suitable example given.