Converts starch into maltose. hydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides so as to remove successive alpha-maltose residues from the non-reducing ends of the chains. Binds 3 Ca(2+) ions per subunit. Monomer. Used in the food industry to prevent bread from staling. Sold under the name Novamyl by Novozymes. Belongs to the glycosyl hydrolase 13 family.