Investigation of the potential of whisky pot ale as a resource to produce high-value sustainable products

Abstract

For every litre of whisky produced, approximately 8 litres of the by-product pot ale are generated, corresponding to an estimated 8.8 billion litres produced annually across Scotland and Ireland. Pot ale is generally discharged either to nearby land or water, although significant environmental concerns regarding both practices have led to research into alternative processing methods, such as using it as feed, and its anaerobic digestion for biogas production. This work attempts to identify potential valorisation opportunities in pot ale through extensive characterisation with the aim of making the whisky production process more sustainable.

Seven samples of malt whisky pot ale were extensively characterised, along with one sample of pot ale from pot still whisky production, and one spent lees and one centrate sample. Soluble protein (mean 10.5 g/L), phosphate (mean 1.95 g/L), potassium (mean 1.24 g/L) and carbohydrates (mean 8.97 g/L) present the most attractive routes for valorisation via a feed or food-grade protein isolate, fertiliser (phosphate and potassium), and fermentation or AD (carbohydrates) for bioenergy. Several valuable phenolic antioxidants were also identified in pot ale, including six derivatives of cinnamic acid and three of benzoic acid. These compounds could have applications in pharmaceuticals, cosmetics and functional foods. The presence of copper at a mean concentration of 2.07 mg/L could complicate downstream treatments for valorisation so this should be removed as a first processing step for pot ale.

Disruption of the solid fraction of pot ale (5% (w/w)), consisting mainly of deactivated yeast cells, could enrich the soluble protein if done efficiently. Yeast contains high concentrations of essential amino acids and a significant amount of protein, with the potential of adding further value to the pot ale protein. Ball milling of pot ale at an agitation speed of 20 Hz and a 1/1 (w/v) bead load achieved an 84% increase in soluble protein. The amino acid composition of the soluble protein after yeast disruption needs to be determined so that it can be seen whether a highly valuable food-grade protein isolate can be produced.

Thesis is embargoed until 31 July 2029.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Sky East UK Ltd
Supervisor	Mark Muldoon (Supervisor) & Panagiotis Manesiotis (Supervisor)