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.
Diastastic enzymes are used in mashing to convert starches from unfermentable long chain starches to shorter chain fermentable sugars. These sugars are then used by the yeast to produce alcohol and CO2. Diastatic power or DP is a measure of how much starch-converting enzyme any given malt contains.