Hydrolyzes barley beta-glucan, lichenan, carboxymethylcellulose and xylan. It shows preferential activity against the larger cellooligosaccharides (cellohexaose and cellopentaose); cellotetraose is the smallest substrate degraded completely. Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Optimum pH is 4.8. Optimum temperature is 43 degrees Celsius. Belongs to the glycosyl hydrolase 5 (cellulase A) family.