Research Articles (Institute for Wine Biotechnology)

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Browsing Research Articles (Institute for Wine Biotechnology) by Author "Chidi, B. S."

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    Determining the impact of industrial wine yeast strains on organic acid production under white and red wine-like fermentation conditions
    (South African Society for Enology and Viticulture, 2015) Chidi, B. S.; Rossouw, D.; Buica, A. S.; Bauer, Florian
    Organic acids are a major contributor to wine flavour and aroma. In the past, the scientific focus has mostly been on organic acids derived from grapes or on the transformation of malic acid to lactic acid by lactic acid bacteria, since these acids contribute significantly to the final total acidity of wine. However, the organic acid concentration and composition also change significantly during alcoholic fermentation, yet only limited information regarding the impact of different yeast strains on these changes has been published. Here we report on changes in organic acid (malic, tartaric, citric, succinic, acetic and pyruvic) composition during fermentation by five widely used industrial wine yeast strains in a synthetic grape must (MS300) reflecting two very different, but both wine-like, fermentation conditions. Samples were obtained from three physiological stages during fermentation, namely the exponential growth phase (day 2), early stationary phase (day 5) and late stationary phase (day 14). These different stages were selected to provide more information on acid evolution throughout fermentation, as well as on the impact of nutritional and environmental conditions during aerobic and anaerobic fermentation. Among other observations, some strains (such as VIN13 and 285) were shown to be generally higher producers of most acids in white and/ or red wine fermentation settings, while other strains (such as DV10) were generally lower acid producers. The data clearly demonstrate that different strains have different acid consumption and production patterns, and this presents a first step towards enabling winemakers to appropriately select strains for acid management during fermentation.
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    Impact of grape temperature at pressing on organic acids and oenological characteristics of Méthode Cap Classique wines
    (South African Society for Enology and Viticulture, 2018) Chidi, B. S.; Mafata, M.; Notshokovu, N. Z.; Van Jaarsveld, F.
    Maintaining the chemical composition of a wine is essential for the wine industry. Although the sugar-acid balance of a wine is of primary sensory importance, individual acids and oenological parameters are equally important. The main focus of this study was to investigate the impact of grape temperature at harvest, on the oenological volatile acidity (VA), titratable acidity (TA), pH and alcohol levels and organic acid (citric, malic, pyruvic and succinic) characteristics of Méthode Cap Classique (MCC) wines during winemaking, produced from grape cultivars obtained from two regions. Chardonnay and Pinot noir grapes were obtained from Robertson (warmer) and Elgin (cooler) regions and were subjected to different temperature treatments, i.e. 0, 10, 25 and 30oC before further processing, including pressing, primary fermentation, blending, tirage, secondary fermentation, riddling and disgorging. Grape temperature was mostly responsible for a significantly higher pH of Robertson (0 and 10ºC) and lower pH (0ºC) of Elgin post-tirage wines. Chardonnay base wines from both regions that were vinified from grapes at lower temperatures (0 and 10oC) were richer in malic- and succinic acid, while Pinot noir wines from both regions were characterised by higher malic-, citric- and pyruvic acid. Pyruvic acid was only detected after the secondary fermentations in wines from both regions. To our knowledge, this study is the first to investigate the influence of grape temperature on the oenological and organic acid characteristics of MCC wines in different regions, and throughout different production stages.