Project number
SAWGRI BD 20-01
Project leaders
Prof Benoit Divol
Dr Evodia Setati
Institution
South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University
Completed
2024
EXECUTIVE SUMMARY
Objectives and Rationale
This project investigated how different wine yeast species and strains manage redox cofactors during alcoholic fermentation and the influence thereof on flavour compound production. Monitoring redox dynamics and assessing environmental factors identifies conditions winemakers may manipulate to potentially enhance yeast persistence and impact on wine characteristics.
Methods
Fermentations were conducted using synthetic grape juice to monitor redox status and metabolite production in various yeast species and strains. A multifactorial experiment assessed the impact of environmental factors, and sensory evaluations were performed on real grape juice fermentations. Next-generation sequencing compared gene expression under oxygenated and unoxygenated conditions.
Key Results
- A lack of NAD+ regeneration leads to yeast’s premature decline.
- Mechanisms to regenerate NAD+ differ between yeasts, resulting in unique metabolic footprints.
- Nicotinic acid deficiency impacts redox balance and fermentation performance.
- Thiamine deficiency impacts the fermentation rate.
- Oxygen could be a lever to alter metabolic footprint and sensory attributes in wine.
Key Conclusion of Discussion
Unlike S. cerevisiae, certain non-Saccharomyces species struggle to ferment due to insufficient NAD+ regeneration. Each yeast’s distinct redox metabolism results in different metabolite production and fermentation performance. Nicotinic acid deficiency results in poor fermentative efficiency and altered metabolic footprint. Oxygenation could be used to impact fermentation kinetics and wine properties.
Take Home Message for Industry
Yeast strain selection and nicotinic acid deficiency are important to consider as they impact fermentation and flavour production. Controlled oxygen can alter wine properties without causing oxidation or sensory defects.
Popular publications
Duncan, J.D., Ortiz-Julien, A., Setati, M.E. and Divol, B., (2023). Production of flavour compounds by wine yeasts is dependent on the management of their intracellular redox balance. IVES Technical Reviews.
Duncan, J.D. and Divol, B., (2023). Fruit salad vs varnish – nitrogen sources and their impact on aroma production in wine. WineLand, (August), pp. 57-60.
Duncan, J.D. and Divol, B., (2022). The role of thiamine in sluggish fermentations and crushed dreams. WineLand, (November), pp. 23-24.