Displays a broad range of substrate specificity, with the capacity to hydrolyze carbohydrates as simple as maltotriose. Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Optimum pH is 6.5-7.5. Optimum temperature is 100 degrees Celsius. Inactive below 40 degrees Celsius. Extremely thermostable. Homodimer. Belongs to the glycosyl hydrolase 57 family.