A new study led by Dr Shiwen Zhuang from the university's International Centre for Brewing and Distilling suggests that raising the wash strength from the industry standard of 8% alcohol by volume (ABV) to between 10% and 14% ABV could lead to substantial environmental and operational improvements.
The 'wash', a beer-like liquid produced after yeast converts sugars into alcohol during fermentation, is then distilled. The research, utilising a model of real-world fermentation and traditional two-pot distillation, found that a wash strength of 14% ABV could reduce energy use and carbon emissions by approximately 16% per litre of pure alcohol produced.
Furthermore, this approach could decrease the volume of 'pot ale' (liquid remaining after the first distillation) by 55% and 'spent lees' (liquid after the second distillation) by over 30%, thereby significantly lowering liquid residues from the distillation process. These findings align with the Scotch whisky industry's ongoing efforts towards net zero targets and improved efficiency.
“"This study highlights the potential environmental and operational benefits of stronger wash. These benefits could be achieved in different ways. Existing distilleries may be able to increase output without expanding fermentation capacity, while new or growing distilleries could produce the same amount of whisky using smaller equipment and lower processing volumes."
Dr Jane White, also an Assistant Professor at Heriot-Watt's International Centre for Brewing and Distilling and co-author, noted potential economic advantages. Reduced volumes of pot ale and spent lees could lower handling, transport, and treatment costs, while preserving valuable materials for recovery and reuse.
The authors acknowledge that challenges remain for widespread adoption, including the need for new mashing approaches for higher fermentable sugars and further study into yeast performance and flavour development. Despite these hurdles, the research offers a valuable framework for enhancing the sustainability of Scotch whisky production.
The research, published in the Journal of the Institute of Brewing, was conducted by Dr Shiwen Zhuang, Dr Jane White, and Professor Chris Boulton. It supports Heriot-Watt University's commitment to the brewing and distilling sector through its proposed Centre for Brewing and Distilling (CABD), which aims to foster innovation and sustainability.
