Addressing consumer style requirements and climate change through genetically directed yeast selection: Excellence® Celsius
Winemakers must walk a delicate balance between market requirements, production costs and ultimately producing wines that are drinkable and of high quality. This challenge seems to get harder every year, and certainly production costs are ever-increasing, no better evidenced than the impacts of COVID on consumables and freight. The climate seems to be highly variable globally, but certainly the overall trend is for warmer temperatures. In 2021 Bordeaux allowed the use of new grape varietals to counter this. Consumers favour wines that have ripe flavours, which of course require ripe grapes. A warming climate makes it easier to grow ripe grapes, but the ancillary factors here are high must sugar and low acid levels, which manifest in the final wine as high alcohol levels and the production thereof requires significant acid additions. Wines can be diluted with water (which diminishes quality) or treated using membrane and mechanical technology (which comes at significant cost) to reduce alcohol levels, and acid additions are never free.
Wouldn’t it be nice if we could counter these factors through the smart use of biotechnology?
Climate effects and wine stylistic trends
Riper flavours require riper fruit which are favoured by consumers, but this arrives in concert with higher juice/must sugar levels and lower acid levels. Juice/must titratable acidity is known to decrease as fruit ripens (Godden et al, 2015). A generally warming climate superimposes added complications on top of these factors, which is perhaps most obvious in old-world regions such as France, as shown in Figure 1 (reproduced from van Leeuwen et al, 2019). Traditionally such regions have had “good” vintages (meaning one with favourable growing conditions thus producing higher quality wines) perhaps a few times per decade, but climate change has meant that these regions can now more frequently produce riper flavours and even need acid additions.
Figure 1. % Alcohol, pH and titratable acidity (g/L H2SO4) in red wines from the Languedoc region of France over 3 decades. Reproduced from van Leeuwen et al, 2019.
The changes in [red] wine composition in this region are clear: higher alcohol levels, higher pH and lower acidity. To a greater or lesser extent these same trends can be observed in other global markets, including Australia.
Hybrid yeast selection via QTL
For discussions on hybrid yeasts see: Bowyer et al, 2017; Marullo et al, 2006; Bowyer and Nogues, 2024. Hybrid yeast strains are those produced through parental strain selection and forced breeding under laboratory conditions. It cannot be stressed strongly enough that this process of yeast breeding is in principle no different to the process that occurs in nature, and this does not involve genetic modification. Historically, selected parental yeast strains have been crossed and the progeny strains examined for various characteristics and the most suitable strain commercialised. This approach is highly intensive and requires significant time to complete.
A more modern method of hybrid selection involves the technique of qualitative trait locus (QTL) targeting, which is facilitated these days by the ability to rapidly sequence yeast DNA. In this technique specific real-world traits (the phenotype) are statistically correlated with observed DNA markers (the genotype), which represents a far more efficient method of progeny strain examination. This methodology significantly improves the efficiency by which new hybrid yeast strains can be commercialised, the most recent example of which is Excellence® Celsius from Lamothe-Abiet. Parental backcrossing can also be used to evaluate the performance of different allelic combinations in progeny strains.
Yeasts vary in their efficiency in converting juice/must sugars to ethanol to the tune of around ± 0.5 % alcohol. In selecting Excellence® Celsius 5 genes were targeted, as noted in Table 1, drawing on the work of Peltier et al, 2019. Excellence® Celsius is homozygous for 86 % of the targeted loci, and as such was deemed the best candidate for commercial trials in 2023/4.
Table 1. Genes targeted via QTL in the development of Excellence® Celsius.
Excellence Celsius™: what does it do?
To put it simply, Excellence® Celsius metabolises a portion of the juice/must sugar and instead of simply producing ethanol and CO2 it produces some alternative secondary metabolites in the forms of glycerol and L-malic acid. Production of these secondary metabolites varies somewhat according to the environmental conditions of the fermentation, but approximate figures are a decrease in final alcohol of around 0.5 %, plus the production of malic acid from 0.8-2 g/L and glycerol at around 2-3 g/L. These parameters are not insignificant and each has a distinct impact on the organoleptic profile of the wine, in addition to the wine chemistry.
Trials vintage 2024 – France
Several trials were conducted across multiple regions in France, including Bordeaux (Merlot), the Rhone Valley (Grenache), and Burgundy (Chardonnay). Key results from the Rhone trial (Grenache) were a decrease in alcohol content of 0.51 % and in the Burgundian trial (Chardonnay) a pH decrease of 0.14 and a corresponding increase in TA of 2.1 g/L (data not shown). The following data pertain to the Bordeaux trial and data are post AF/MF (Figure 2a-f).
Figure 2. Must parameters are indicated where relevant. Yeats A and B are competitor strains. (a) [alcohol] % v/v; (b) [glycerol] g/L; (c) pH; (d); titratable acidity (g/L tartaric acid equivalents) (e) concentration of L-malic (must) and L-lactic (final wine) acids; (f) concentrations of fermentation esters by aroma type (ug/L). Fresh fruit esters are ethyl esters of fatty acids, starchy/waxy esters are higher alcohol acetates and florals are the remaining esters.
Ultimately, chemical parameters such as those quantified in Figure 2 are important, but it is arguably more important that an appropriate wine style is forthcoming. To that end, a sensory evaluation was made comparing the control wine and that made from Excellence® Celsius, the results for which are given in Figure 3. As expected, Excellence® Celsius delivered a wine more noticeable acid on the palate, palate freshness and reduced roundness, all of which are functions of the increased acid and lower alcohol levels. Other sensory aspects were found to be similar for both wines.
Figure 3. A radar plot of the sensory characteristics of the Control and Excellence® Celsius wines from the Bordeaux trial (Merlot).
Trials vintage 2024 – Australia
Trials in Australia were conducted on Cabernet sauvignon (Coonawarra) and Shiraz (Adelaide Hills and Coonawarra). The following data pertain to the Coonawarra Shiraz data set (Figure 4); other data are not shown. Must parameters were: Baumé 13.4, pH 3.45, TA 7.10 g/L TAE and an addition of tartaric acid of 1 g/L was made around 3 Bé.
Figure 4. (a) [alcohol] % v/v; (b) pH (c) titratable acidity (g/L tartaric acid equivalents).
Sensory analysis of the wines reflected those found for the French trial, where the wine made with Excellence® Celsius showed more freshness and acidity on the palate, with slightly decreased roundness relative to the control (Excellence XR™; data not shown).
Discussion
The reduction in ethanol production offered by Excellence® Celsius was reliable at the ~0.5 % level across all trials, with corresponding diversion of the sugar metabolism to the production of L-malic acid and glycerol. Given that the organic acids found in wine constitute a dynamic and interactive matrix it is perhaps not surprising that the final wine titratable acidity levels are not as linear as one might initially expect. The Coonawarra Shiraz trial wine showed an increase of
Summary
Even though winemakers are being pushed to deliver ripe wine styles to market biotechnological tools exist to make this task easier. Excellence® Celsius was genetically selected to provide a partial or complete solution to the problems generated by ripe fruit without compromising quality through dilution or increased production costs due to dealcoholisation technologies. Excellence® Celsius is non-GMO and offers lower alcohol production in addition to acidification through its production of L-malic acid, and this is also offset by the concurrent production of glycerol.
BHF wishes to thank The Australian and New Zealand Grapegrower and Winemaker for permission to reproduce this article. Subscription information can be found here.
Paul K. Bowyer1 and Galdric Nogues2
1BHF Technologies, Unit 1, 11-13 Wells Rd, Oakleigh VIC 3166. 2Lamothe-Abiet, Z. A. Actipolis, avenue Ferdinand de Lesseps, 33610 CANEJAN/Bordeaux – France
References
Bowyer, P. K., Chancholle, L. and Mennesson, A. (2017) Yeast breeding as a tool for wine stylistic manipulation, The Australian and New Zealand Grapegrower and Winemaker, October Issue, 73-76.
Bowyer, P. K. and Nogues, G. (2024) Modern commercial yeast selection Part 2: Hybrids, The Australian and New Zealand Grapegrower and Winemaker, May Issue, 82-88.
Godden, P., Wilkes, E. and Johnson, D. (2015), Trends in the composition of Australian wine 1984–2014. Australian Journal of Grape and Wine Research, 21: 741–753. doi:10.1111/ajgw.12195
Marullo, P., Bely, M., Masneuf-Pomarède, I., Pons, M., Aigle, M., Dubourdieu, D.; Breeding strategies for combining fermentative qualities and reducing off-flavor production in a wine yeast model, FEMS Yeast Research, Volume 6, Issue 2, 1 March 2006, Pages 268–279, https://doi.org/10.1111/j.1567-1364.2006.00034.x
Peltier, E., Friedrich, A., Schacherer, J. and Marullo, P., 2019. Quantitative trait nucleotides impacting the technological performances of industrial Saccharomyces cerevisiae strains. Frontiers in Genetics, 10, p.683.
Van Leeuwen, C., Destrac-Irvine, A., Dubernet, M., Duchêne, E., Gowdy, M., Marguerit, E., Pieri, P., Parker, A., De Resseguier, L. and Ollat, N., 2019. An update on the impact of climate change in viticulture and potential adaptations. Agronomy, 9(9), p.514.