Starch is a staple food present in water-insoluble granules in many economically important crops. It is composed of two glucose polymers: the linear α-1,4-linked amylose and amylopectin with a backbone of α-1,4-glycosidic bonds and α-1,6-linked side chains. To dissolve starch completely in water it needs to be heated; when it cools down too much the starch solution forms a thermo-irreversible gel. Amylomaltases (EC 184.108.40.206) are enzymes that transfer a segment of an α-1,4-D-glucan to a new 4-position in an acceptor, which may be glucose or another α-1,4-D-glucan. Acting upon starch, amylomaltases can produce cycloamylose or a thermoreversible starch gel, both of which are of commercial interest.