South Africa Wine Research Projects 2025

3. OENOLOGY RESEARCH COMPLETED PROJECT

THE ROLE OF PHENOLIC LEVELS IN SPARKLING WINES: OPTIMISATION OF JUICE YIELD EXTRACTION IN SPARKLING WINE PRODUCTION

WW JT 22-01 Dr Jose-Luis Aleixandre-Tudo, South African Grape and Wine Research Institute,

Stellenbosch University Project completed: 2023

AIM AND INDUSTRY RELEVANCE: Maximising juice recovery has been a key objective in sparkling wine production; however, press fractions were often perceived as lower quality due to their elevated phenolic content. This study re-evaluated that assumption by examining how phenolics influence the sensory characteristics of still and sparkling wines. Blending free-run and press fractions provided a more accurate representation of phenolic increases than tracking individual press phases. Traditional absorbance at 280 nm proved to be an unreliable phenolic indicator, whereas UPLC-measured total phenolic content (TPC) offered a more accurate assessment. The ABS 262 nm/328 nm ratio was effective in estimating press fraction levels in still wine musts but not in sparkling wine musts, likely due to grape compositional variability. Phenolic trends in musts did not consistently persist throughout fermentation, highlighting the complexity of chemical interactions. pH was strongly correlated with press fraction levels, supporting its combined use with phenolic data for better process control. Cold maceration had a limited impact on phenolic extraction in still white wines, which were less sensitive to increasing press fractions. Sparkling wines, however, exhibited more pronounced sensory differences with rising phenolic levels. Hydroxycinnamic acids and flavanols were identified as useful markers of free-run and press fractions, respectively. Spectroscopy based methods, including UV-Vis and MIR, demonstrated promise for rapid phenolic monitoring. To optimise pressing operations and maintain wine quality, producers should collaboratively monitor phenolic markers (hydroxycinnamic acids, flavanols) and ph. Spectroscopy-based tools offer a practical solution for real-time decision-making—especially vital in sparkling wine production, where phenolics significantly influence sensory perception.

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SOUTH AFRICA WINE RESEARCH 2025