NOVELTY - Producing sugar mixture solution from solid biomass feedstock involves adding solid biomass feedstock comprising hemicellulose, cellulose, and lignin into counter current extraction apparatus; adding acidic solution comprising primary solvent and miscible bulking agent into distal inlet port; contacting solid biomass feedstock with acidic solution within apparatus to form solution extract comprising mixture of lignin and sugar from solid biomass feedstock; recovering solution extract through the apparatus; and separating lignin from solution extract to give concentrated sugar solution.    USE - For producing a sugar mixture solution from a solid biomass feedstock comprising hemicellulose, cellulose, and lignin (claimed).    ADVANTAGE - The method is economic; reduces the overall cost of reagent and waste disposal; and produces at least 40 % of the theoretical yield of sugar from the solid biomass feedstock. The presence of the sugar yield enhancing agent increases the yield of sugar by at least 10% compared to the same solution in the absence of the sugar yield enhancing reagent.    DETAILED DESCRIPTION - Producing a sugar mixture solution from a solid biomass feedstock comprising hemicellulose, cellulose, and lignin using a counter current extraction apparatus, where the counter current extraction apparatus comprises a tube having a proximal end and a distal end, where the proximal end comprises a proximal inlet port and a proximal outlet port, and the distal end comprises distal inlet port and a distal outlet port; and at least one material-transporting element within the tube such that a first material introduced in the proximal inlet port is transported towards the distal outlet port and a second material introduced in the distal inlet port is transported towards the proximal outlet port, and where the material-transporting element intimately mixes the first material and the second material within the counter current extraction apparatus, involves: introducing a solid biomass feedstock comprising hemicellulose, cellulose, and lignin into the proximal inlet port of the counter current extraction apparatus and transporting the solid biomass feedstock towards the distal outlet port; introducing an acidic solution comprising a primary solvent and a miscible bulking agent into the distal inlet port and transporting the acidic solution towards the proximal outlet port; contacting the solid biomass feedstock with the acidic solution within the counter current extraction apparatus under conditions sufficient to produce a solution extract comprising a mixture of lignin and sugar from the solid biomass feedstock, where the step of contacting the solid biomass feedstock with the acidic solution fluidizes the solid biomass feedstock as the solid biomass feedstock is transported from the proximal inlet port to the distal outlet port of the counter current extraction apparatus such that the total amount of solid recovered from the distal outlet port is less than or equal to 20% of the total solid biomass feedstock introduced into the proximal inlet port; recovering the solution extract through the proximal outlet port of the counter current extraction apparatus; and separating lignin from the solution extract to produce a concentrated sugar solution that is free of lignin.