Co-fermentation as a strategy for sustainable Scotch whisky production

Climate pressures and rising water constraints are driving the Scotch whisky industry toward more resource-efficient production, including the adoption of high gravity fermentations. However, these conditions place significant stress on yeast, often resulting in reduced fermentation efficiency, lower alcohol yields, and undesirable flavour outcomes.
This PhD project has explored co-fermentation, the use of more than one yeast strain, as a strategy to improve fermentation performance under high-gravity conditions while maintaining flavour quality.
A diverse yeast library was curated and systematically screened using a combination of phenotyping, applied clustering algorithms, design of experiments (DoE), and tree-based predictive modelling. From a reduced experimental dataset, the outcomes of over 1,200 potential strain combinations were inferred, enabling the selection of representative co-fermentations for detailed study. Fermentation performance, volatile composition, and metabolomic profiles were assessed and compared to parental monocultures.
Results demonstrated that co-fermentation behaviour is not uniform, but instead falls into distinct interaction types: antagonistic, neutral, and synergistic. Importantly, synergistic co-fermentations produced significantly higher alcohol yields under high-gravity conditions compared to monocultures, while maintaining broadly comparable flavour profiles. Multivariate analysis of volatile compounds revealed that co-fermentations do not converge to a single profile but instead occupy a bounded and tuneable flavour space, a potential novel and desirable outcome for blenders and distillers.
Metabolomic analysis identified early accumulation patterns of mevalonate as a potential biomarker of synergistic interactions, suggesting a role for coordinated lipid metabolism and sterol pathway flux in determining compatibility between strains. This provides a mechanistic framework linking co-fermentation performance with intracellular metabolic state, which can be translated into a decision-making framework for industry adoption.
Altogether, the work has reframed co-fermentation from a trial-and-error approach to a predictable and optimisable system. But crucially, the findings have demonstrated that co-fermentation can enhance alcohol yield, supporting water-efficient production, without compromising flavour integrity.