NOVELTY - Increasing the level of soluble 5C saccharides produced from lignocellulosic biomass, comprises: providing a fractionated lignocellulosic biomass comprising a solid fraction comprising optionally, insoluble 5C oligosaccharide, cellulose, and lignin and a first liquid fraction at a first temperature and a first pressure; acidifying the fractionated lignocellulosic biomass to form a second liquid fraction; optionally, separating the solid fraction from the second liquid fraction; and optionally, hydrolyzing the second liquid fraction to form 5C saccharides.    USE - The method is useful for increasing the level of soluble 5C saccharides produced from lignocellulosic biomass.    ADVANTAGE - The method provides yield of at least 68% of the soluble 5C saccharides, and minimizes the formation of degradation products.    DETAILED DESCRIPTION - Increasing the level of soluble 5C saccharides produced from lignocellulosic biomass, comprises: (a) providing a fractionated lignocellulosic biomass comprising a solid fraction comprising optionally, insoluble 5C oligosaccharide, cellulose, and lignin and a first liquid fraction at a first temperature and a first pressure comprising soluble 5C saccharides consisting of 5C oligosaccharides, xylose, arabinose, lyxose, and/or ribose, where the soluble 5C saccharides are present at a first level; (b) acidifying the fractionated lignocellulosic biomass to form a second liquid fraction comprising soluble 5C saccharides at a second lever and at a second temperature, where the second level is higher than the first level; (c) optionally, separating the solid fraction from the second liquid fraction; and (d) optionally, hydrolyzing the second liquid fraction to form 5C saccharides consisting of 5C oligosaccharides having fewer mer units, xylose, arabinose, lyxose, and/or ribose. INDEPENDENT CLAIMS are included for:    (1) a product produced by the method;    (2) a composition, comprising soluble 5C oligosaccharides capable of being membrane separated, and water, where the composition has a pH of 1.5-6, and the soluble 5C oligosaccharides have 2-15 mer units; and    (3) a method of increasing the level of fermentative or catalytic product produced from lignocellulosic biomass comprising the steps (a)-(d) as above per se, and fermenting, catalyzing, or fermenting and catalyzing the 5C saccharides to form the fermentation product, and/or catalytic product.