Exochitinase that generates exclusively chitobiose from chitotetraose, chitohexaose, and colloidal high-molecular mass chitin. Random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins. Inhibited by the pseudosugar allosamidin A. Optimum pH is 7.3. Optimum temperature is 55 degrees Celsius. By chitin. The N-terminus is blocked. Belongs to the glycosyl hydrolase 18 family. Chitinase class II subfamily.