Enhanced winemaking outcomes and wine style diversification through provision of fit-for-purpose yeast starter cultures
It is common practice for winemakers to choose particular yeasts in pursuit of desired wine styles. Availability of new yeasts that impart novel flavour profiles or that accentuate specific varietal characters can provide winemakers with an expanding array of options to achieve stylistic flexibility. This project aims to facilitate the development of wine styles with distinctive flavour profiles and the production of existing wine styles with lower input costs, with a particular focus on the contribution of yeast to red wine flavour. A broad approach is being taken to microbial modulation of wine flavour, including harnessing the overall genetic diversity of yeast germplasm (both within and outside the S. cerevisiae species) with the objective of establishing yeast ‘flavour profiles’ and accompanying genomic markers. Classical breeding, nutagenesis and interspecies hybridisation, guided by genomic insights into ‘what each genome brings to a wine strain’, are being applied to generate novel wine strains that modulate red wine flavour, display appropriate flocculation behaviour, produce low levels of offflavours and exhibit stable performance.
Benchmarking yeast strain impact upon wine composition
The fermentation characteristics of approximately 100 genomesequenced yeast strains have been evaluated. More than 600 fermentations have been completed in chemically defined and real grape juice, with the resultant wines analysed for key yeast-derived wine flavour compounds. Significant variation has been observed for most flavour compounds analysed, and some non-volatile components such as succinic acid and glycerol. Correlations have been established between genomic datasets and a strain’s ability to produce the ‘rose’ aroma compounds 2-phenyl ethanol (2-PE) and 2-phenylethyl acetate (2-PEA). Similarly, correlations have been established for the production of volatile sulfur compounds. These datasets enhance knowledge of commercially available wine yeast strains and provide the basis for ongoing development of novel fit-for-purpose starter cultures.
Boosting floral aromas in red and white wines
Novel yeast mutants that produce high levels of 2-PE and 2-PEA were derived from a popular commercial wine yeast and had their genomes sequenced. This analysis revealed key mutations in a small number of genes that are important for the biosynthesis of ‘rose’-like floral aromas. In addition, one of the novel mutants was used to make pilotscale Shiraz and Chardonnay wines. Importantly, the mutant displayed fermentation characteristics indistinguishable from its parent; the resulting wine will undergo sensory assessment in the coming year. The ability for winemakers to specifically ‘dial up’ the floral aromas in their wine through choice of yeast will provide them with a readily applied and immediate option to shape wine style.
Toni Garcia Cordente