β-Amylase (EC 3.2.1.2, saccharogen amylase, glycogenase) is an enzyme with the systematic name 4-α-D-glucan maltohydrolase.

[2][3][4] It catalyses the following reaction: This enzyme acts on starch, glycogen and related polysaccharides and oligosaccharides producing beta-maltose by an inversion.

Working from the non-reducing end, β-amylase catalyzes the hydrolysis of the second α-1,4 glycosidic bond, cleaving off two glucose units (maltose) at a time.

β-amylase is present in an inactive form prior to seed germination.

The optimum pH for β-amylase is 4.0–5.0[5] They belong to glycoside hydrolase family 14.