The Impact of All Grains in Fermentation Methodology on Whisky Wash Production Using Grists Comprised of Malted Barley and Malted Rye

During production of Scotch whisky, wort is often separated from insoluble components of the grist prior to fermentation. However, some whisky spirits are produced using an alternative All Grains In (AGI) approach in which insoluble material is conserved into the fermentation and even distillation phases of production. In Scotland (and globally), AGI methodology is generally used during the production of grain whisky, and there is increasing interest in its application for development of unique aroma congeners and improved production efficiency (as compared to filtered processes). There is likewise interest in the utility of this approach as applied to cereals associated with processing challenges (e.g. rye). The present study establishes the impact of AGI processing in grists containing varying proportions of malted barley and malted rye, comparing indicators of process efficiency and wort/wash quality with filtered protocols. Mashes (laboratory scale and pilot scale) were prepared using filtered and AGI approaches, with fermentation performance indicators tracked across a 114 h period. Compared to filtered approaches, AGI fermentation resulted in a wash with increased ethanol yield (8.18% ABV for 100% malted barley AGI compared with 7.41% ABV for filtered), pH, free amino nitrogen (182.4 mg/L for 100% malted rye AGI compared with 129.8 mg/L for filtered), dynamic viscosity and residual α-amylase activity, as well as decreased residual fermentable sugar content. The findings indicate potential yield benefits for use of AGI fermentation methodology as compared to use of filtered wort substrates, particularly where applied to wort derived from grists containing high proportions of malted rye.