South Africa Wine Research Projects 2025

3. OENOLOGY RESEARCH COMPLETED PROJECT

DOES INTRACELLULAR COENZYME AVAILABILITY LIMIT YEAST IMPACT ON WINE FLAVOURS?

SAGWRI BD 20-01 Prof Benoit Divol and Prof Evodia Setati, South African Grape and Wine Research Institute, Stellenbosch University Project is co-funded by Danstar Project completed: 2023

AIM AND INDUSTRY RELEVANCE: This project inve stigated how different wine yeast species and strains manage redox cofactors during alcoholic fermentation and how these processes influence flavour compound production. The aim was to identify environmental conditions that winemakers can manipulate to enhance yeast performance and influence wine sensory characteristics. Redox dynamics and metabolite production were monitored in several yeasts, including Saccharomyces cerevisiae , Lachancea thermotolerans , and Torulaspora delbrueckii , using synthetic grape juice. A multifactorial experiment explored the effects of nutrients such as tryptophan, thiamine, and nicotinic acid, while sensory evaluations were performed on wines fermented from real grape juice. Next generation sequencing was used to analyse gene expression under oxygenated and non oxygenated conditions. Key findings indicated that insufficient NAD ⁺ regeneration resulted in early yeast decline, with each yeast species exhibiting distinct mechanisms for maintaining redox balance and producing unique metabolic profiles. Nicotinic acid deficiency significantly impacted fermentation performance and redox stability, while thiamine deficiency mainly influenced fermentation rate. Oxygen emerged as an effective tool for modulating metabolic pathways and sensory properties without causing oxidation or sensory faults. In S. cerevisiae , NAD(H) levels decreased rapidly after mid-exponential growth, with strain-specific variations noted. Non- Saccharomyces yeasts, particularly weaker fermenters, showed significant redox imbalances. Oxygen supplementation accelerated fermentation and enhanced biomass production. In real grape juice fermentations, oxygen exposure improved yeast performance and altered the sensory profile, while vitamin supplementation led to minimal sensory changes, suggesting sufficient nutrient levels in the juice. This research offered valuable insights into yeast physiology and fermentation management, highlighting the significance of nutrient balance and oxygen as factors for influencing wine style. Yeast strain selection and the prevention of nicotinic acid deficiency are crucial for efficient fermentation and desirable flavour development. Controlled oxygen exposure during early fermentation can be strategically utilised to modify wine characteristics without compromising quality, providing winemakers a practical tool for tailoring sensory outcomes.

SOUTH AFRICA WINE RESEARCH 2025

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