TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The pretreatment reactor: comprises extruder, first drain (where the first liquid fraction exits the pretreatment reactor through the first drain), eductor (where the eductor is adapted to transfer the solid matrix to the hydrolysis reactor), conical reactor, and continuously stirred tank reactor; is adapted to separate a pretreated composition, where the pretreated composition comprises a first liquid fraction and a solid matrix; and is adapted to continuously feed the solid matrix into the hydrolysis reactor. In the pretreatment reactor, the eductor comprises a steam inlet, where the steam inlet is adapted such that the solid matrix is transferred to the hydrolysis reactor in response to an elevated pressure of steam. The hydrolysis reactor: comprises an extruder, and second drain (where the second liquid fraction exits the transferring means through the second drain); is adapted to separate a hydrolyzed composition comprising second liquid fraction and insoluble lignin fraction. The continuously stirred tank reactor comprises a flexible blade impeller associated with a motor, where the motor is associated with the continuously stirred tank reactor. The apparatus further comprises: many water injection units associated along the length of the pretreatment reactor, where the water injection units are adapted to allow adjustment of temperature and pressure of the pretreatment reactor by injection through the water injection units of a solution having known temperature and comprising water; and many temperature control units associated along the length of the pretreatment reactor, where the temperature control units are adapted to allow adjustment of temperature of the pretreatment reactor by injection of a fluid having a known temperature.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The pretreatment step occurs at a temperature and pressure below the critical point of at least one component of the first supercritical, near-critical, or sub-critical fluid, where the pretreatment step is performed at 150-300 degrees C and pressure of 50-115 bar. The biomass has a residence time of 1-5 minutes in the pretreatment step. In the method of treating biomass, at least one of the solid matrix and first liquid fraction are cooled to a temperature below that of the pretreatment step, where the solid matrix and first liquid fraction are cooled to 20-90 degrees C. The method of treating biomass further comprises: a first separation step after the pretreatment step and prior to the hydrolysis step, where the solid matrix and first liquid fraction are separated using extruder or centrifugal press; second separation step after the hydrolysis step, where the lignin fraction and second liquid fraction are separated; second hydrolysis step, where the second liquid fraction is contacted with a third near-critical or sub-critical fluid to produce a third liquid fraction comprising glucose monomers, and the third near-critical or sub-critical fluid comprises water and optionally acid; reducing the pressure exerted on the solid matrix such that lignin precipitates, after the hydrolysis step, where the lignin is recovered by skimming; and xylo-oligosaccharide hydrolysis step, where the first liquid fraction is contacted with a fourth near-critical or sub-critical fluid to produce a fourth liquid fraction comprising xylose monomers, where the fourth near-critical or sub-critical fluid comprises water and optionally acid. The pretreatment step and hydrolysis step are continuous. The solid matrix has a residence time of 1-30 seconds in the hydrolysis step. The hydrolysis step occurs at a temperature and pressure above the critical point of at least one component of the second supercritical or near-critical fluid, where the hydrolysis step occurs at 275-450 degrees C, and pressure of 200-250 bar. The solid matrix is kept at greater than or equal to 185 degrees C from the beginning of the pretreatment step through at least the end of the hydrolysis step. The method of treating biomass further comprises: cooling at least one of the lignin fraction and the second liquid fraction after the hydrolysis step, where at least one of the lignin fraction and the second liquid fraction is cooled to 180-240 degrees C; or flash cooling at least one of the lignin fraction and second liquid fraction, where at least one of the lignin fraction and second liquid fraction is flash cooled to 20-90 degrees C. The second hydrolysis step occurs at 220-320 degrees C (preferably 240-300 degrees C), and a pressure of 30-90 bar (preferably 35-85 bar). The second liquid fraction has a residence time of 1-30 seconds in the second hydrolysis step. In the method of treating biomass, at least one product of the second hydrolysis step is cooled to a temperature less than that of the second hydrolysis step. The pressure exerted on the solid matrix is reduced to less than or equal to 105 kPa after the hydrolysis step. The xylo-oligosaccharide hydrolysis step occurs at 220-320 degrees C (preferably 240-300 degrees C), and a pressure of 30-90 bar (preferably 35-85 bar). The second liquid fraction has a residence time of 1-30 seconds in the xylo-oligosaccharide hydrolysis step. The fourth liquid fraction is cooled after the xylo-oligosaccharide hydrolysis step to a temperature lower than that of the xylo-oligosaccharide hydrolysis step. In method (I): fractionating comprises contacting the biomass with a first reaction fluid comprising water and optionally carbon dioxide, where the first reaction fluid has temperature and pressure above the critical point of carbon dioxide, and at least one of the temperature and pressure of the first reactive fluid is below the critical temperature and critical pressure of water; the xylo-oligosaccharides in the first liquid fraction have 2-25 mer units, and the xylo-oligosaccharides in the second liquid fraction have 2-15 mer units; and the yield of the xylose is at least 70% of theoretical yield. The method (II) is continuous. In the method (II): reducing the temperature of the reaction mixture to a temperature below the critical point of water comprises contacting the reaction mixture with a composition comprising water with or without acid (less than 10 wt.%); fractionated biomass is prepared by contacting the biomass with a first reaction fluid comprising water and optionally carbon dioxide, where the first reaction fluid has temperature and pressure above the critical point of carbon dioxide, and at least one of the temperature and pressure of the first reactive fluid is below the critical temperature and critical pressure of water; pre-heating is carried out at 245-255 degrees C and pressure of 200-260 bar; contacting the slurry with a second reaction fluid is carried out at 358-380 degrees C and a pressure of 200-260 bar; reducing the temperature of the reaction mixture is carried out at 260-280 degrees C and a pressure of 200-260 bar; and the yield of the glucose is at least 63% of theoretical yield. Preferred Components: The first supercritical, near-critical, or sub-critical fluid comprises less than 10% of carbon dioxide. The first liquid fraction comprises xylose oligosaccharides in an amount greater than 50% of the maximum theoretical yield. The second liquid fraction comprises cello-oligosaccharides. The second supercritical or near-supercritical fluid does not include an acid. In the third and fourth liquid fractions: the acid is present in a catalytic amount, preferably in an amount less than 1%; and the acid comprises hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfonic acid, phosphoric acid, phosphonic acid, nitric acid and/or nitrous acid. The third liquid fraction comprises glycolaldehyde, which is present in an amount of at least 10% of the theoretical maximum yield. In the method (I), the aqueous acid comprises organic acid or inorganic acid, where the inorganic acid is dilute sulfuric acid. EXAMPLE - Biomass slurry in water was fed into a pretreatment reactor and heated. Optionally, carbon dioxide was introduced as a catalyst into the pretreatment reactor. After pretreatment, the fractionated biomass was cooled by the introduction of cooling fluid (water with or without acid (preferably inorganic acid)). The liquid fraction containing xylose was separated using a solid/liquid separator from the solid fraction containing cellulose and lignin, where the pretreatment of the biomass was carried out at 220-250 degrees C, pressure of 100 bar and residence time of 1-1.6 minutes. The pretreated biomass slurry was preheated and subjected to hydrolysis in a hydrolysis reactor using supercritical and near-critical fluids comprising supercritical water (prepared by heating water stream in a furnace under pressure) and supercritical carbon dioxide. The hydrolyzed slurry was quenched with water (with or without dilute acid (preferably sulfuric acid)) to slow down the hydrolysis reaction and prevent the formation of degradation products. The use of acid in the quench hydrolyzes the cello-oligosaccharides to glucose monomers. The hydrolyzed slurry is further cooled with cooling fluid (water). After solid/liquid separation of the slurry, the liquid phase containing hexose sugars (including glucose monomer (59.5 %)) and solid phase containing mostly lignin (50-70 %) were obtained, where the hydrolysis of the pretreated biomass was carried out at 353 plus minus 2.5 degrees C and pressure of 222 plus minus 5.7 bar.