Process for producing bioethanol from a lignocellulosic vegetable raw material, comprising the successive steps of: - a) pretreatment of the lignocellulosic vegetable raw material in order to separate the cellulose, the hemicelluloses and the lignins contained in this lignocellulosic vegetable raw material, the pretreatment comprising the following successive steps consisting in: • (i) destructuring the lignocellulosic vegetable raw material by placing it in the presence of a mixture containing formic acid and water, at a reaction temperature between 95°C and 110°C; • (ii) then, at atmospheric pressure and prior to any hydrolysis and fermentation action, in separating: * on the one hand, the solid phase mainly consisting of said cellulose capable of then being hydrolysed and fermented for the production of bioethanol; * and on the other hand, the liquid phase, containing in particular, in a solution of water, the formic acid, the lignins and the hemicelluloses; - b) enzymatic hydrolysis of said solid phase; - c) alcoholic fermentation of the products resulting from said hydrolysis step, which are capable of being fermented for the production of bioethanol, characterized in that the process for producing bioethanol comprises, prior to the enzymatic hydrolysis step b), a step of partial elimination of the lignins that is carried out by means of a treatment with sodium hydroxide, followed by a washing step intended to eliminate the residual sodium hydroxide before the enzymatic hydrolysis step, so as to obtain a residual overall level of lignins, expressed as percentage by weight, which is included in a range determined by a lower limit (Llow), and an upper limit (Lupp), respectively equal to 0.30% and 4% and in that in order to obtain conditions of acidification before the enzymatic hydrolysis step, the process comprises a step for re-acidification of the mixture, which is carried out by means of a mixture of acids of determined pKa which are acetic acid and formic acid. - a) pretreatment of the lignocellulosic vegetable raw material in order to separate the cellulose, the hemicelluloses and the lignins contained in this lignocellulosic vegetable raw material, the pretreatment comprising the following successive steps consisting in: • (i) destructuring the lignocellulosic vegetable raw material by placing it in the presence of a mixture containing formic acid and water, at a reaction temperature between 95°C and 110°C; • (ii) then, at atmospheric pressure and prior to any hydrolysis and fermentation action, in separating: * on the one hand, the solid phase mainly consisting of said cellulose capable of then being hydrolysed and fermented for the production of bioethanol; * and on the other hand, the liquid phase, containing in particular, in a solution of water, the formic acid, the lignins and the hemicelluloses; • (i) destructuring the lignocellulosic vegetable raw material by placing it in the presence of a mixture containing formic acid and water, at a reaction temperature between 95°C and 110°C; • (ii) then, at atmospheric pressure and prior to any hydrolysis and fermentation action, in separating: * on the one hand, the solid phase mainly consisting of said cellulose capable of then being hydrolysed and fermented for the production of bioethanol; * and on the other hand, the liquid phase, containing in particular, in a solution of water, the formic acid, the lignins and the hemicelluloses; * on the one hand, the solid phase mainly consisting of said cellulose capable of then being hydrolysed and fermented for the production of bioethanol; * and on the other hand, the liquid phase, containing in particular, in a solution of water, the formic acid, the lignins and the hemicelluloses; - b) enzymatic hydrolysis of said solid phase; - c) alcoholic fermentation of the products resulting from said hydrolysis step, which are capable of being fermented for the production of bioethanol,