Quantifying the impact of increasing wash strength for Scotch malt whisky production: a modelling study

Why was the work done: High gravity fermentation (ca 8% ABV) is used in the production of Scotch malt whisky but the impact of increasing wash strength on fermentation and distilling has not been quantified, especially in relation to environmental and operational performance. How was the work done: A representative scenario of a 200 hL wash at 8% ABV was used to model wash strengths of 10-14% ABV under two conditions: the same wash volume (Condition 1) and the same ethanol mass (Condition 2). All scenarios were assessed quantitatively. What are the main findings: In Condition 1, increasing wash strength enhanced batch production capacity but may require a larger spirit still or multiple distillation batches. In Condition 2, higher wash strength reduced batch processing volumes, enabling the use of smaller vessels without compromising the capacity for ethanol production. Distilling energy dominated the total energy demand, whereas fermenter cooling energy was negligible. On the basis of a litre of pure alcohol (100% ABV) and an annual target basis, increasing wash strength from 8 to 14% ABV progressively reduced energy use and carbon footprint by 15.8-16.1%, while also reducing post-distillation discharge volumes by 55.0% in pot ale and 30.4% in spent lees. Why is the work important: This study provides quantitative evidence of the effects of increasing wash strength (8-14% ABV) on the operational and environmental performance in Scotch malt whisky production. This supports process innovation, capacity planning, and industrial decarbonisation strategies.