Browsing by Author "Jolly, N. P."

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    Characterisation of non-saccharomyces yeasts using different methodologies and evaluation of their compatibility with malolactic fermentation
    (South African Society for Enology and Viticulture, 2017) Du Plessis, H. W.; Du Toit, M.; Hoff, J. W.; Hart, R. S.; Ndimba, B. K.; Jolly, N. P.
    Although Saccharomyces cerevisiae is the yeast species predominantly used for alcoholic fermentation, non-Saccharomyces yeast species are also important because they produce secondary metabolites that can contribute to the final flavour and taste of wines. In this study, 37 strains representing seven non-Saccharomyces species were characterised and evaluated for potential use in wine production, as well as for their effects on malolactic fermentation (MLF). Contour-clamped homogeneous electric field (CHEF) gel electrophoresis and matrix-assisted laser desorption ionisation using a time-of-flight mass spectrometer (MALDI-TOF MS) were used to verify species identity and to determine intra-species variation. Extracellular enzyme production, malic acid degradation and the fermentation kinetics of the yeasts were also investigated. CHEF karyotyping and MALDI-TOF MS were useful for identifying and typing Hanseniaspora uvarum, Lachancea thermotolerans, Candida zemplinina (synonym: Starmerella bacillaris) and Torulaspora delbrueckii strains. Only H. uvarum and Metschnikowia pulcherrima strains were found to have β-glucosidase activity. M. pulcherrima strains also had protease activity. Most of the strains showed limited malic acid degradation, and only Schizosaccharomyces pombe and the C. zemplinina strains showed mentionable degradation. In synthetic wine fermentations, C. stellata, C. zemplinina, H. uvarum, M. pulcherrima and Sc. pombe strains were shown to be slow to medium fermenters, whereas L. thermotolerans and T. delbrueckii strains were found to be medium to strong fermenters. The effect of the yeasts on MLF varied, but inhibition was strain dependent.
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    The effect of non-Saccharomyces yeasts on fermentation and wine quality
    (South African Society for Enology and Viticulture, 2003) Jolly, N. P.; Augustyn, O. P. H.; Pretorius, I. S.
    Research has shown that non-Saccharomyces yeast strains can be detected throughout wine fermentation. Non-Saccharomyces yeasts can therefore influence the course of fermentation and also the character of the resultant wine. Previously it was shown that four non-Saccharomyces species, i.e. Kloeckera apiculata, Candida stellata, Candida pulcherrima and Candida colliculosa, predominated in grape must at the start of fermentation. In this study these four yeasts were used singularly and in combination with an industrial wine yeast (Saccharomyces cerevisiae strain VIN 13) to ferment must on a laboratory scale. The resultant wine was analysed for ethanol, volatile acidity, total S02 and glycerol. Results show that, in comparison with the industrial wine yeast, the non-Saccharomyces yeast strains could not ferment all the sugar. Furthermore, while the individual non-Saccharomyces-fermented wines had different chemical analyses, the wines fermented by the combinations were similar to the wine produced by the industrial yeast only. In subsequent, small-scale winemaking trials some of the wines produced by combined fermentations were judged to be of better quality than those produced by the S. cerevisiae only. However, this quality increase could not be linked to increased ester levels.
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    Non-Saccharomyces yeast and lactic acid bacteria in Co-inoculated fermentations with two Saccharomyces cerevisiae yeast strains : a strategy to improve the phenolic content of Syrah wine
    (MDPI, 2019) Minnaar, P. P.; Du Plessis, H. W.; Jolly, N. P.; Van Der Rijst, M.; Du Toit, M.
    Syrah must was co-inoculated with mixed cultures of Saccharomyces + O. oeni/Lb. plantarum and Saccharomyces + non-Saccharomyces + O. oeni/Lb. plantarum to evaluate the effect on phenolics and sensory attributes. Reference wines were produced by S. cerevisiae. Malvidin-3-O-glucoside, flavan-3-ols, flavonols and phenolic acids were quantified using a RP-HPLC technique. Physicochemical characteristics and sensory attributes were measured. Total acidity and alcohol in mixed co-inoculations were different from reference wines. The concentration of l-malic acid was 7-times less in mixed co-inoculations. Mixed co-inoculations had ca. 1.3-times more malvidin-3-O-glucoside and phenolic acids than reference wines. Flavan-3-ols and flavonols were not different between mixed co-inoculations and reference wines. Acidity and astringency were least in mixed co-inoculations. Mouthfeel and bitterness least in S. cerevisiae wines. Tasters preferred mixed co-inoculated wines. Mixed co-inoculation is a strategy to contemplate for Syrah vinification but the modalities of inoculation need further investigation. Success depends on a suitable combination of yeast/bacteria and consideration of strain variation.
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    The occurrence of non-Saccharomyces yeast strains over three vintages in four vineyards and grape musts from four production regions of the Western Cape, South Africa
    (South African Society of Enology & Viticulture, 2003) Jolly, N. P.; Augustyn, O. P. H.; Pretorius, I. S.
    The role of non-Saccharomyces yeasts in wine production has been extensively debated and there is growing evidence that non-Saccharomyces yeasts play an important role in wine quality. It has been suggested that metabolites formed by some non-Saccharomyces species may contribute to wine quality. Recently a comprehensive, longterm research programme was launched by role players in the South African wine industry, whose aims include the isolation, characterisation and preservation of the natural yeast biodiversity of the Western Cape. As part of the programme, this paper investigates the presence of non-Saccharomyces yeast species over three vintages in four vineyards and musts in four distinct areas of the Western Cape. Samples were taken and the non-Saccharomyces yeast isolates were characterised by biochemical profiling and pulse field gel electrophoresis. In total 720 yeasts representing 24 species were isolated. Predominant species found in the must samples, i.e. Candida stellata, Kloeckera apiculata, Candida pulcherrima and Candida colliculosa, should have the most impact on subsequent fermentation.
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    The role and use of non-saccharomyces yeasts in wine production
    (South African Society for Enology and Viticulture, 2006) Jolly, N. P.; Augustyn, O. P. H.; Pretorius, I. S.
    The contribution by the numerous grape-must-associated non-Saccharomyces yeasts to wine fermentation has been debated extensively. These yeasts, naturally present in all wine fermentations, are metabolically active and their metabolites can impact on wine quality. Although often seen as a source of microbial spoilage, there is substantial contrary evidence pointing to a positive contribution by these yeasts. The role of non-Saccharomyces yeasts in wine fermentation is therefore receiving increasing attention by wine microbiologists in Old and New World wine producing countries. Species that have been investigated for wine production thus far include those from the Candida, Kloeckera, Hanseniaspora, Zygosaccharomyces, Schizosaccharomyces, Torulaspora, Brettanomyces, Saccharomycodes, Pichia and Williopsis genera. In this review the use and role of non-Saccharomyces yeast in wine production is presented and research trends are discussed.
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    Saccharomyces cerevisiae, non-saccharomyces yeasts and lactic acid bacteria in sequential fermentations : effect on phenolics and sensory attributes of South African syrah wines
    (South African Society for Enology and Viticulture, 2017) Minnaar, P. P.; Du Plessis, H. W.; Paulsen, V.; Ntushelo, N.; Jolly, N. P.; Du Toit, M.
    Wine consumers predominantly use visual, sensory and textual descriptors as quality/preference indicators to describe olfactory sensations. In this study, different wines were analysed to generate relevant chemical and sensory characterisation data and attributes. Sequential inoculation of Syrah grape must was performed with a combination of Saccharomyces yeast, non-Saccharomyces yeasts and lactic acid bacteria for the possible improvement of Syrah wine quality. Selected anthocyanins, flavan-3-ols, flavonols and phenolic acids were quantified in Syrah wines using the reversed-phase high-performance liquid chromatography photodiode array detection (RP-HPLC-DAD) technique. Sensory (descriptive evaluation) and physicochemical/oenological parameters (Winescan® and OenoFoss™) results were compared to phenolic compound concentrations. Phenolic compound concentrations increased in Syrah wines made with a combination of a Saccharomyces reference yeast, non-Saccharomyces yeasts and lactic acid bacteria. Syrah wines made with a combination of Metschnikowia pulcherrima + Saccharomyces cerevisiae + Oenococcus oeni, and M. pulcherrima + S. cerevisiae + Lactobacillus plantarum, had higher flavonol concentrations compared to wines made without lactic acid bacteria. Syrah wines made with a combination of Saccharomyces cerevisiae (Sc) + Oenococcus oeni (LAB1) were highest in phenolic acid concentrations. Syrah wines made with a combination of M. pulcherrima + S. cerevisiae + L. plantarum had higher total anthocyanins than wines made without lactic acid bacteria. Syrah wine sensory attributes, viz. mouthfeel and astringency, correlated with a combination of lactic acid bacteria and yeast treatments. Syrah wines made with a combination of yeast and lactic acid bacteria (LAB) scored highest in overall quality. Indications are that the S. cerevisiae reference yeast retained more phenolic compounds during fermentation when compared to wines made with a combination of non-Saccharomyces yeasts and LAB. The improved red colour of Syrah wines may be achieved by sequential inoculation with non-Saccharomyces yeast and LAB. This could be beneficial where winemakers use grape cultivars with low anthocyanin levels in the grape skin to produce wines of improved quality.
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    The use of Candida pulcherrima in combination with Saccharomyces cerevisiae for the production of Chenin blanc wines
    (South African Society of Enology & Viticulture, 2003) Jolly, N. P.; Augustyn, O. P. H.; Pretorius, I. S.
    Wine fermentations are conducted by naturally occurring or selected industrial wine yeast strains of Saccharomyces cerevisiae. However, non-Saccharomyces yeasts also occur naturally in fermenting grape musts, especially in the initial stages of the fermentation. It has been speculated that these yeasts can contribute to the overall characteristics of the wine. Generally, it is accepted that Kloeckera apiculata is the predominant non-Saccharomyces yeast species in grape must. However, it was shown previously that Candida pulcherrima was the predominant non-Saccharomyces yeast species in a grape must after sedimentation and prior to inoculation with commercial wine yeast. Subsequently, this yeast was investigated in laboratory and small-scale wine fermentations of Chenin blanc wine. As it could not ferment grape juice to dryness on its own, it was used in combination with a S. cerevisiae wine yeast strain. The effect of SO2, di-ammonium phosphate (DAP), pH and temperature on the growth of C. pulcherrima was also investigated. In combined fermentations, no change in overall fermentation rate or standard wine chemical analyses could be observed in comparison to a control S. cerevisiae fermentation. However, wine production in three consecutive years showed that the wine produced by the combined fermentation was of higher quality than that produced by the S. cerevisiae only.