A diastase (/ˈdaɪəsteɪz/; from Greek διαστασις, "separation") is any one of a group of enzymes which catalyses the breakdown of starch into maltose. Alpha amylase degrades starch to a mixture of the disaccharide maltose, the trisaccharide maltotriose, which contains three α (1-4)-linked glucose residues, and oligosaccharides known as dextrins that contain the α (1-6)-linked glucose branches.
Diastase was the first enzyme discovered. It was extracted from malt solution in 1833 by Anselme Payen and Jean-François Persoz, chemists at a French sugar factory. The name "diastase" comes from the Greek word διάστασις (diastasis) (a parting, a separation) because, when beer mash is heated, the enzyme causes the starch in the barley seed to transform quickly into soluble sugars and hence the husk to separate from the rest of the seed. Today, "diastase" refers to any α-, β-, or γ-amylase (all of them hydrolases) that can break down carbohydrates.
The commonly used -ase suffix for naming enzymes was derived from the name diastase.
When used as a pharmaceutical drug, diastase has the ATC code A09AA01 (WHO).
Amylases can also be extracted from other sources including plants, saliva and milk.