The Evolution of Dextrins During the Mashing and Fermentation of All-malt Whisky Production

Abstract

The production of malt whisky involves the mashing of barley malt, followed by the fermentation of the resulting wort without further treatment. While this process has many parallels to the production of an all-malt beer, one of the main differentiating steps during substrate preparation is the inclusion of a boiling step for the wort in the production of beer. Other than the destructive action of the boiling process on microorganisms, the boiling also destroys all malt enzyme activity. Since a typical whisky wash is not boiled it carries through a certain proportion of microbial activity associated with the malt, but more importantly it retains some enzyme activity that has been activated during the malting and mashing processes. The changes in sugars and dextrins during both mashing and fermentation of the resulting wash were investigated. Evidence of the continuous amylolytic activity during an unboiled, all-malt wash fermentation is shown; while no ongoing amylolytic activity could be deduced during the fermentation of a boiled all-malt wort. Furthermore, the data suggests that the amylolytic activity during mashing and fermentation are different with regards to α-amylase action linked to its multiple-attack action pattern as a function of substrate conformation, temperature, and effectiveness of potential hydrolytic events.

Letter to the Editor: Update on Knowledge Regarding Starch Structure and Degradation by Malt Enzymes (DP/DU and Limit Dextrinase)

“…Both of these enzymes are very active during mashing. The combined action of these enzymes can efficiently degrade starch amylose and amylopectin, but predominantly operate up to 2 units from the branch points, so there will be a large proportion of residual 'limit' dextrins, containing at least 4-8 glucose units 8,26 . However, the smallest dextrins found in all-malt wort are the trisaccharides panose (6 2 α-glucosyl-maltose) and iso-panose (6α-maltosyl-glucose) 3 .…”

“…These give some indication of the structures and properties of both linear and branched dextrins which can help us to appreciate their importance in determining wort fermentability, since some of them are easily degraded to fermentable substrates, while others can only be partially, or slowly degraded, or are limit dextrins and hence cannot be fully hydrolysed by the standard set of starch degrading enzymes (α-amylase, β-amylase and limit dextrinase 8,12,13 ). Vriesekoop et al 26 further elucidated the actions and activity of the main starch degrading enzymes α-amylase, β-amylase and limit dextrinase, and describe in some detail the turnover of dextrins during mashing and fermentation of brewing (boiled) and distilling (unboiled) type worts. They confirmed the previous suggestion 8 that there is a dynamic equilibrium as larger dextrins are hydrolysed and then further degraded and debranched to produce smaller dextrins.…”

“…Vrieskoop et al 26 suggest that there is a dynamic equilibrium as larger dextrins are hydrolysed and then debranched, and it is clear that there is an underlying concentration of dextrins that cannot be attacked by any of the active malt enzymes or utilized by yeast during fermentation 8 . As a result, there is a residue of unfermentable dextrins that still requires further study 26 .…”

“…As a result, there is a residue of unfermentable dextrins that still requires further study 26 . This might include 4-to 7-glucose unit dextrins containing glucosyl-1,6-maltotriose 12,13 , (-maltotetraose, -maltopentaose and -maltohexaose) which cannot be hydrolysed by limit dextrinase or pullulanase.…”

Comparison of fermentation results and quality of the agricultural distillates obtained by application of commercial amylolytic preparations and cereal malts

“…The activity of α-amylase results in an increase in (shorter) dextrins; while β-amylase rapidly removes a maltose moiety from the non-reducing end of all dextrins. If the concerted activity of malt α-and β-amylases was sufficiently random, then it could be expected that this would result in a general decrease in the concentration of dextrins [56].…”