Exploiting yeast diversity in whisky fermentations for biocatalysis of desirable flavour compounds

Yeast is an important component in producing flavourful fermented products. The Scotch Whisky industry currently only uses four different yeast strains all belonging to <i>Saccharomyces cerevisiae</i>. In recent years, the brewing and wine industries have proven that a variety of yeasts can impart flavourful notes, and this has prompted research into alternative yeasts for whisky production. In this study, a variety of non-<i>Saccharomyces</i> yeasts were investigated for their potential of becoming new Scotch Whisky yeasts. While most of the yeast strains tested had a decreased fermentation performance compared to the tested commercial distilling yeast strains, yeast strains of <i>Dekkera bruxellensis</i> and <i>Schizosacchaormyces pombe</i> showed high sugar to ethanol conversion. Flavourwise, the yeast strains tested showed a variety of different flavours resulting in different ratios of detected congeners opening a field of wider flavour research. The flavour differences could not be linked to differences between species, <i>Saccharomyces</i> spp. tested showed a large variety in produced congeners. A correlation between degree of fermentation and flavour could be found with completed fermentations being more sweet, <i>fruity</i>, and <i>floral </i>and less complete fermentations having increased <i>feinty</i>, cereal and <i>sulphur </i>notes. <i>D. bruxellensis</i> CBS 11269 was shown to be especially <i>fruity</i>. The congener production across four different yeast strains and how they were influenced by different fermentation conditions (time, temperature, original gravity, pitching rate) was investigated. The results showed that the yeast strains had the largest impact, but the fermentation conditions also significantly influenced the congener ratios. Of the assessed factors, temperature and original gravity were discovered to have the largest impact.<br/><br/>To examine the flavour differences between yeast strains, Napping was implemented as a new quick sensory technique for Scotch Whisky and produced similar product separation as Quantitative Descriptive Analysis and gas chromatography – mass spectrometry. Furthermore, the flavour and congener changes from wash to low wines and new make spirit were investigated. The result was that assessing the flavour and congener profile on wash and low wine level is sufficient for screening purposes and drastically reduces the workload. Additionally, the alcohol by volume before distillation does not impact the flavour and congeners detected in the spirit if the same distilling regime is used. Pre-treatment (boiling, autoclaving, filtration) of wort before fermentation was also assessed to investigate different ways of reducing the impact of the microflora in wort but all three techniques had too large an impact on the fermentation performance and congener development and would not be recommended for industrial applications.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral Thesis

Year dc:date.issued

2022

Author dc:creator

• Daute, Martina

Advisors dc:contributor.advisor

• Walker, Graeme
• Grigor, John

• Yeast
• Fermentation
• Whisky
• Non-Saccharomyces
• Spirit
• Sensory

Language dc:language

eng

Identifier

oai:rke.abertay.ac.uk:studenttheses/0b7ac2a4-4e10-4414-a8d1-b8abb52739b2

OAI identifier oai:identifier

oai:rke.abertay.ac.uk:studenttheses/0b7ac2a4-4e10-4414-a8d1-b8abb52739b2