NOVELTY - Method for pretreating cellulose for fermentation in aqueous environment, involves grinding biomass to reduce its particle size, adding liquid to the ground biomass, soaking the slurry, heating the slurry at a first pressure greater than atmospheric pressure, reducing the pressure of the slurry, reducing the temperature of the slurry, adding enzymes to the slurry, determining whether the enzymes used require preliminary enzymatic hydrolysis, and performing preliminary enzymatic hydrolysis on the slurry.    USE - The method is useful for pretreating cellulose for fermentation in aqueous environment (claimed).    DETAILED DESCRIPTION - Method for pretreating cellulose for fermentation in aqueous environment, involves (a) (i) grinding biomass to reduce its particle size, (ii) adding liquid to the ground biomass to create a slurry, (iii) soaking the slurry, (iv) heating the slurry at a first pressure greater than atmospheric pressure, (v) reducing the pressure of the slurry, (vi) reducing the temperature of the slurry, (vii) adding enzymes to the slurry, (viii) determining whether the enzymes used require preliminary enzymatic hydrolysis, and (ix) performing preliminary enzymatic hydrolysis on the slurry if the enzymes used require preliminary enzymatic hydrolysis, (b) (i) performing the above-mentioned steps (i)-(ix), (ii) performing fermentation at a temperature lower than the temperature of the preliminary enzymatic hydrolysis on the slurry if the enzymes used require preliminary enzymatic hydrolysis, and (iii) performing combined enzymatic hydrolysis and fermentation on the slurry if the enzymes used do not require preliminary enzymatic hydrolysis, or (c) (i) performing the above-mentioned steps (i)-(iv), (ii) determining the particle size of the slurry and regrinding the slurry at the first pressure if the particle size is above a first value, (iii) reducing the pressure of the slurry, (iv) determining the particle size of the slurry and regrinding the slurry if the particle size is above the first value, (v) determining a water absorption of the slurry and resoaking the slurry if the water absorption is below a second value, (vi) determining an amount of cellulose hydrolyzation of the slurry and reheating the slurry if the amount of cellulose hydrolyzation is below a third value, (vii) reducing the temperature of the slurry, (viii) adding enzymes to the slurry, (ix) determining whether the enzymes used require preliminary enzymatic hydrolysis, (x) performing preliminary enzymatic hydrolysis on the slurry if the enzymes used require preliminary enzymatic hydrolysis, (xi) performing fermentation at a temperature lower than the temperature of the preliminary enzymatic hydrolysis on the slurry if the enzymes used require preliminary enzymatic hydrolysis, and (xii) performing combined enzymatic hydrolysis and fermentation on the slurry if the enzymes used do not require preliminary enzymatic hydrolysis.