The Oxford Companion to Beer definition of
Diastatic Power (DP) is the total activity of malt enzymes that hydrolyze starch to fermentable sugars. The starch-degrading enzymes contributing to this process are alpha-amylase, beta-amylase, limit dextrinase, and alpha-glucosidase. The driving force for DP appears to be beta amylase, which usually correlates better with DP than the other starch-degrading enzymes and has the highest activity of all starch-degrading enzymes in malt. Behind malt extract, DP is usually considered the second most important malt quality measurement. For complete conversion of starch to sugars, high levels of barley malt DP are especially important when adding substantial amounts of unmalted adjunct to the mash tun during brewing. See adjuncts. Mashing converts malt starch into fermentable sugars; however, beta amylase and other starch-degrading enzymes are inactivated as the temperature during mashing increases and DP disappears. There is a dilemma in this phenomenon in that as temperatures rise, starch becomes gelatinized and is a better substrate for starch-degrading enzymes. The term “DP” had its origins with the discovery of diastase in barley malt in 1833 by two French chemists, Anselme Payen and Jean-François Persoz. They precipitated diastase from an aqueous mixture of milled barley and found that small amounts could liquefy starch to form sugars, and that it was unstable at high temperatures. This was one of the first reports of the properties of an enzyme. The suffix -ase, commonly used for naming enzymes, was derived from the name diastase. Methodologies for measuring malt DP were developed in the late 19th and early 20th centuries.
Bamforth, Charles W. “Barley and malting.” In: Scientific principles of malting and brewing , 21–44. St. Paul, MN: American Society of Brewing Chemists, 2006.
Briggs, Dennis, E. “The biochemistry of malting.” In: Malts and malting, 133–228. London: Blackie Academic & Professional, 1998.
Buchholz, Klaus, Volker Kasche, and Uwe T. Bornscheuer. “Introduction to enzyme technology.” In: Biocatalysts and enzyme technology, 1–25. Weinheim, Germany: Wiley–VCH, 2005.
Stanley H. DukeandCynthia A. Henson