TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Composition: The molecules solubilized out of biomass including lignin and polysaccharides are fragmented into smaller fragments, less than 3000 (preferably less than 300) g/mol. The weight ratio of water and lactic acid or lactic acid oligomer is 95:5-0.1:99.9. The fraction of biomass in reactor is 2-75 wt.%. Preferred Components: The biomass originates from wood, straw plants, peat or any other plant based crude material including other biomass based crude materials. Preferred Conditions: The temperature and pressure of continuous reactor can be regulated at 100-350 degrees C and 1-50 bars. The residence time of biomass and/or its components including and polysaccharides and lactic acid and/or lactic acid oligomers containing mixture is 2 minutes to 15 hours. Preferred Method: The biomass based fibers and lignin, polysaccharides and its components and compounds of smaller molecular weight are separated from water and lactic acid and/or lactic acid oligomers by distillation, extraction, crystallization, nanofiltration, ultrafiltration or reverse osmosis. The lactic acid and/or lactic acid oligomer is recycled.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The continuous reactor comprises pressure vessel provided with temperature regulator and including stirred tank or pipe reactor, preferably pipe reactor with or without recirculation. The product stream is led out from continuous pipe reactor through pressure drop valve. The reaction mixture containing biomass and/or its components and lactic acid and/or lactic acid oligomers is fed to reactor having no gas phase including pipe reactor by using pressure increasing pump, preferably piston pump or gear pump. EXAMPLE - A reactor was charged with 88% lactic acid aqueous solution (97.5 wt.%) and chopped wood (2.5 wt.%). The reactor was immersed into oil bath, the temperature was elevated at 180 degrees C, and cooking was continued until 4 hours. As dark mixture product was recovered, lignin was solubilized and wood material was disintegrated. The fiber structure was largely degraded, and easy to pump fluid was formed. The recovered black liquor was conducted into pipe reactor. The residence time was controlled stepwise through pumping speed for 5 minutes to 2 hours. Samples were recovered corresponding each residence time at outlet. Lignin was detected to be in a form of far reached degradation, with molecular weight of 200-1000 g/mol.