Specialty malts are extensively used in brewing industry to enhance beer taste, mouthfeel and colour. Such malts are produced under conditions of high temperature, which results in non-enzymatic browning and an increased concentration of aromatic constituents, primarily through the action of Maillard chemistry. The majority of Scotch malt whisky is made using lightly kilned malted barley that yields only delicate aromas to the finished product, and the characteristics differentiating whisky of one distillery from another is primarily introduced by varied fermentation, distillation and maturation practices. With demand increasing for greater product variety, there is increasing interest in the use of specialty malts as a tool for aroma control. However, current knowledge relating to the use of high colour malt for whisky production is largely anecdotal, and the substantial differences between distillery and brewery practice necessitate investigation.
Our research group at Heriot-Watt University are investigating the impact of malt roasting conditions on efficiency of wort/wash production and resulting aroma volatile composition of distillate. Samples of pot still malt were roasted at laboratory scale and incorporated to distillery grist across a range of inclusion rates (10-50% w/w). Experimental grists were mashed, fermented and double-distilled in 2 L copper pot stills. Grain processing characteristics were assessed using industry recognised methodology and distillate aroma was assessed using GC-MS. Designed experimentation was employed to produce response surface models, assessing the impact of roasting temperature and time on measured qualities in malt, wort, wash and spirit.
The results demonstrated that although use of roasted malt for distillate production reduced alcohol yield, there was a substantial increase in number and concentration of heat-derived flavour-active molecules in the distillate. Appropriate selection of malt roasting conditions and grist composition were identified as key for limiting impact of high colour malts on ethanol yield whilst retaining a significant impact on aroma volatile profile. The findings of our study have considerable implications for the commercial use of roasted malts in whisky production, and for the production of roasted malts directed towards the distilling industry.
