There is disclosed a process for the hydrolysis of cellulose comprising the sequential steps (a) mixing cellulose with a viscosity below 900 ml/g with an aqueous solution to obtain a liquid, wherein particles comprising cellulose in said liquid have a diameter of maximum 200 nm, wherein the temperature of the aqueous solution is below 35° C., and wherein the pH of the aqueous solution is above 12, (b) subjecting the liquid to at least one of the steps: (i) decreasing the pH of the liquid with at least 1 pH unit and (ii) increasing the temperature by at least 20° C., and (c) hydrolyzing the cellulose. Moreover there is disclose glucose manufactured according to the method and ethanol manufactured from the glucose. Advantages include that the cellulose is hydrolyzed faster and to a greater extent after the treatment. The yield is increased.