A review of malting and malt processing for whisky distillation

This paper encompasses a re‐evaluation of published literature and data regarding wort attenuation in malt distilleries raising questions and discussing how the conventional wisdom has changed over time and what questions still need to be answered. Current knowledge is summarized in the following four points: (a) Under normal malting conditions, starch granules are partially degraded by a combination of α ‐amylase and α ‐glucosidase. This complex can open up the granule at specific sites on the surface and create characteristic ‘pin‐hole’ lesions, which may be widened by secondary hydrolysis by α ‐ and β ‐amylase, limit dextrinase and α ‐glucosidase (maltase). (b) All of these diastatic enzymes can survive mild kilning, probably by forming heat stable complexes on and within the starch granules and can continue a complete degradation of starch when mashed at ambient temperatures with glucose as the end product. (c) At normal mashing temperatures, starch granules gelatinize and dissolve with a concomitant rapid degradation to glucose, maltose, maltotriose and dextrins ranging from degree of polymerization (DP) 4 to > DP20. If there is immediate wort boiling after run‐off, this is the final composition of starch derived carbohydrates according to the conventional paradigm. (d) All malt worts also contain a small amount of panose, isopanose as well as glucosyl maltodextrins, based on a core of 6 2 ‐ α ‐glucosyl maltose (panose) or 6‐ α ‐maltosyl glucose (isopanose), which are remnants of the α ‐amylase/glucosidase degradation of granular starch. These dextrins are resistant to the action of debranching enzymes and their concentration may vary between 4 and 8% of the malt extract, depending on the degree of modification of the host starch granules. They may be created at the active sites of this enzyme complex when the granule is gelatinized. In a conventional mash of unboiled distilling wort, the spectrum of wort dextrins produced from gelatinized starch is reduced to true ‘limit’ dextrins of DP4–8 by continued α ‐amylolysis during early fermentation. These dextrins will contain side chains of either maltose or maltotriose residues surrounding the α ‐1,6‐glucosidic linkage and can be debranched by limit dextrinase during late fermentation, leaving only the above glucosyl maltodextrins dextrins in the spent wash. Copyright © 2016 The Institute of Brewing & Distilling