The aim of this study3 was to select and evaluate naturally bred Saccharomyces cerevisiae intra-genus hybrids for the production of wine with enhanced fruity and tropical fruit aromas, but low volatile acidity levels.3
Sauvignon blanc wine aroma is comprised of compounds emanating directly from the grapes, compounds produced by the wine yeast Saccharomyces cerevisiae, such as esters (fruity aroma) and yeast mediated compounds, e g volatile thiols (tropical fruit aroma).1 However, S. cerevisiae yeasts vary in their ability to develop the full aroma potential of Sauvignon blanc grapes as some have an inability to release volatile thiols.4 S. cerevisiae yeasts can also produce volatile acidity (VA) during alcoholic fermentation,2 although excessive levels are mainly caused by lactic acid bacteria (LAB), acetic acid bacteria (AAB) and wild yeasts.
Materials and methods
A total of 136 S. cerevisiae hybrids, parental yeasts and commercial reference yeasts were evaluated in laboratory-scale fermentation trials in previously frozen Sauvignon blanc grape must (total sugar = 21.9°B; total acidity = 9.3 g/ℓ; pH = 3.28). Wines were subjected to chemical analyses and descriptive sensory evaluation three months after bottling. Judges were requested to indicate aroma intensities and to specify the most prominent aroma/s perceived, i e ‘tropical fruit’; ‘vegetative’ or ‘floral’. Wines with the most prominent fruity aromas were also subjected to GC-MS analysis to quantify flavour compounds, namely esters, total fatty acids and higher alcohols.7,8
Results and discussion
Wine chemical and sensory quality are affected by the yeast strain used to carry out the alcoholic fermentation.5,6 As a result, differentiation of yeast strains is essential to ensure that the correct yeast strain is used to inoculate grape must.3 The CHEF DNA karyotyping proved useful to differentiate between the closely related S. cerevisiae hybrid strains descending from mutual parental yeast strains. Additionally, MALDI-TOF/MS biotyping was successfully deployed to distinguish between commercial reference strains, parental strains and hybrid strains. This study, therefore, showed that MALDI-TOF/MS biotyping is a reliable yeast identification method that complements CHEF DNA karyotyping.
All the hybrids fermented the grape must at a rate similar, or even faster, to commercial reference and parental strains. Chemical analyses showed that some promising hybrids produced wine with parameters equal to, or better than that of the commercial reference and parental strains, especially concerning VA production. The same observation was made following descriptive sensory evaluation, as these hybrids also produced wines that were perceived to have enhanced tropical fruit aromas in comparison to the reference wines.
Gas chromatography analyses on selected wines based on descriptive sensory evaluation showed that some of the hybrids produced wines with ester levels that were comparable to those produced by commercial reference strains, while having lower VA levels. Some hybrids also produced wines with enhanced tropical fruit aromas. Fourteen hybrids complied with the selection criteria indicated in the aims, were further investigated.
Improved hybrid strains were identified compared to commercial references and parental yeast strains. These hybrids showed lower VA formation, whilst producing aromatic Sauvignon blanc wines. In addition, this study showed that classical mating is still practical to produce novel yeast strain with desired traits. Further studies with these promising yeast strains would be required to evaluate their performance under industry conditions.
A laboratory-scale trial was undertaken to evaluate Saccharomyces cerevisiae intra-genus hybrid yeasts for the production of Sauvignon blanc wine with enhanced fruity and tropical aromas and lower VA. Commercially available yeasts with “thiol-releasing” abilities recommended for the production of aromatic Sauvignon blanc, were included as references. Most intra-genus hybrids produced wines with VA levels significantly lower than those produced by the references. Low VA forming hybrids also produced wines with tropical fruit aromas. Overall, 14 hybrids showed promise for future commercial trials.
The authors wish to thank the Agricultural Research Council (ARC) and University of the Western Cape (UWC) for the infrastructure and/or financial support; Anchor Bio-Technologies for financial support and the NRF/THRIP; as well as the wine technology subdivision for technical support. Winetech is also thanked for supporting the initial yeast development projects which preceded this one.
- Bovo, B., Carlot, M., Fontana, F., Lombardi, A., Soligo, S., Giacomini, A. & Corich, V., 2015. Outlining a selection procedure for Saccharomyces cerevisiae isolated from grape marc to improve fermentation process and distillate quality. Food Microbiology 46, 573 – 581.
- Cordente, A.G., Cordero-Bueso, G., Pretorius, I.S. & Curtin, C.D., 2013. Novel wine yeast with mutations in YAP1 that produce less acetic acid during fermentation. FEMS Yeast Research 13, 62 – 73.
- Hart, R., Jolly, N., Mohamed, G., Booyse, M. & Ndimba, B., 2016. Characterisation of Saccharomyces cerevisiae hybrid yeasts selected for low volatile acidity formation and the production of aromatic Sauvignon blanc wine. African Journal of Biotechnology 15, 2068 – 2081.
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– For more information, contact Rodney Hart at email@example.com.