Endo-1,4-beta-xylanase involved in the hydrolysis of xylan, a major structural heterogeneous polysaccharide found in plant biomass representing the second most abundant polysaccharide in the biosphere, after cellulose. Endohydrolysis of (1->4)-beta-D-xylosidic linkages in xylans. Optimum pH is 4.0. Optimum temperature is 60 degrees Celsius. Glycan degradation; xylan degradation. Belongs to the glycosyl hydrolase 11 (cellulase G) family.