NOVELTY - Producing sweet juice from lignocellulosic substrate by enzymatic hydrolysis comprises supplementing cellulases with supported beta -glucosidase in a second reactor (2), which is separated from a first reactor (1) for enzymatic hydrolysis of lignocellulose in which the substrate, previously pretreated, is contacted with a cellulase solution; and introducing hydrolysate from an outlet of the first reactor to separate and extract cellulases before introducing into the second reactor.    USE - The process is useful for the preparation of the sweet juice, which is useful for the production of biofuels.    ADVANTAGE - The process economically improves the recycling of the enzymes thus facilitating the extraction of beta -glucosidase from the reaction medium.    DETAILED DESCRIPTION - Producing sweet juice from lignocellulosic substrate by enzymatic hydrolysis comprises supplementing cellulases with supported beta -glucosidase in a second reactor (2), which is separated from a first reactor (1) for enzymatic hydrolysis of lignocellulose in which the substrate, previously pretreated, is contacted with a cellulase solution; and introducing hydrolysate from an outlet of the first reactor to separate and extract cellulases before introducing into the second reactor, where the process comprises lignocellulose conversion phase, sweet juice production phase and complete emptying of reactors phase. An INDEPENDENT CLAIM is included for a device for the production of sweet juice by enzymatic hydrolysis from lignocellulosic substrate comprising at least one first reactor for enzymatic hydrolysis of lignocellulose, where the reactor is provided with at least one pipe for the introduction of substrate and the cellulase solution, at least one pipe to extract the H1 converted juice and sending it to at least one filter medium (3) placed in the reactor outlet, and at least a means for separation, which is preferably an ultra filtration membrane for extracting the cellulases from the hydrolysate, optionally a heat exchanger at the outlet of the first reactor, at least a second reactor comprising supported beta -glucosidase, connected to at least one means for separation, by at least one pipe, where the second reactor is equipped at the outlet of at least one filtering medium (4) and at least one pipe for the extraction of H2 flux constituted of the hydrolysate having low soluble oligomers, at least one pipe for introducing at least a part of the H2 flux in a contactor (5) and at least one pipe for returning at least a part of the flux H2 in the first reactor, and at least one contactor, equipped with at least one pipe for the introduction of the new substrate, one pipe for extracting the produced sweet juice (H3) and at least one pipe for the exit of the new substrate impregnated with cellulases and its introduction into the first reactor.    DESCRIPTION OF DRAWING(S) - The figure shows the schematical representation of the preparation of the sweet juice.    First reactor (1)    Second reactor (2)    Sweet juice (H3)    Filter medium (3, 4)    Contactor. (5)