Co-fermentation in the Whisky industry for water sustainably and flavour development.

As the climate crisis continues to impact upon the natural resources essential to whisky production, utilisation of high gravity brewing and higher fermentation temperatures may be essential to reduce water requirements. However, this would necessitate use of yeast adapted to these conditions, therefore Co-fermentation has been proposed as a potential strategy to
maintain high ethanol yields and the production of desirable flavour compounds.

The success of co-fermentations is however subject to optimal yeast interactions and pairings. Strain ratios and inoculation modes, including timings can all be altered to influence positive yeast interactions and optimise fermentations, but this is highly strain specific and further dependant on fermentation conditions.

Strategies were introduced in this research to reduce workload and predict specific conditions at which optimal yeast pairings can be achieved utilising over 50 (conventional and non-conventional) yeast strains. Firstly, individual strains have been categorized via hierarchical clustering, based on fermentation performance (viability, pH, ABV%) under controlled conditions (4% YPD at 30°C), and stress tested under increasing temperature and gravity. Categorisation, by default, could reveal numerous potential pairings from fewer co-fermentations, but was primarily used to identify strain characteristics and tolerances and inform co-fermentation pairs. Secondly, a Design of Experiments (DOE) approach was used to create models that can predict optimal pairings and conditions, identifying strain pairs that show potential for optimisation.

From 220 unique strain pairs tested so far, a diverse range of yeast pairings has been revealed and the importance of strain pairing to the success of co-fermentations is evident, however Schizosaccharomyces pombe notably pairs well with many strains (both brewing and distilling strains of Saccharomyces, and non-conventional yeast), whilst maintaining good tolerances of elevated gravities and temperatures. In addition, preliminary data indicates the choice of second strain has a noticeable impact on the resultant congener profile of these S. pombe fermentations.