An indigenous &lt;I&gt;Saccharomyces cerevisiae&lt;/I&gt; yeast strain isolated from Paarl regional Shiraz grapes to enhance Shiraz wine typicity

Michell Williams,Wesaal Khan,Rodney Hart,Nombasa Ntushelo

doi:10.20870/oeno-one.2021.55.2.4552

Abstract

Wine yeast starter cultures differ in their ability to release aroma-enhancing metabolites associated with typical varietal wines. Therefore, this study investigated an indigenous Saccharomyces cerevisiae isolated from Paarl regional Shiraz grapes for the release of, amongst others, volatile thiols (aroma compounds traditionally associated with white cultivars, especially Sauvignon blanc) during the 2016 and 2017 vintages using Shiraz grape must. Chemical analyses of final wines showed that the indigenous strain i.e., NI6 produced Shiraz wines lower volatile acidity (VA) and acetic acid concentrations than wines produced with reference strains i.e., WE372 and MERIT, respectively. This was further supported by descriptive sensory evaluations of wines, as NI6 wines had typical Shiraz varietal aromas and flavours, i.e.,“berry”, “jammy”, “smoky” and “spicy and peppery”. This yeast strain also produced wines with more 3-mercapto-1-hexanol (3MH), a volatile thiol that imparts black currant aromas in red wines, than both red wine reference strains in 2016. Both red wine reference strains, however, produced red wines with higher ester compounds (imparts “fruity” aroma) concentrations than strain NI6. Nonetheless, the ability of NI6 to consistently release volatile thiols during both vintages is advantageous for Shiraz wine typicity. Overall, this study showed that wines with a positive correlation with black and/or fruits aromas and flavours also had volatile thiol levels above its sensory detection thresholds, which indicates that ester compounds are not solely responsible for Shiraz wine fruity aromas and flavours as was traditionally reported.

Highlights

Red wines are said to have many health benefits such as the reduced risk of heart disease, depression some cancers (Shukla and Singh, 2011), moderate consumption of no more than two glasses per day were previously recommended (Arranz et al, 2012; O’Keefe et al, 2007)
This study investigated an indigenous Saccharomyces cerevisiae isolated from Paarl regional Shiraz grapes for the release of, amongst others, volatile thiols during the 2016 and 2017 vintages using Shiraz grape must
Chemical analyses of final wines showed that the indigenous strain i.e., NI6 produced Shiraz wines lower volatile acidity (VA) and acetic acid concentrations than wines produced with reference strains i.e., WE372 and MERIT, respectively

Summary

Introduction

Red wines are said to have many health benefits such as the reduced risk of heart disease, depression some cancers (Shukla and Singh, 2011), moderate consumption of no more than two glasses per day were previously recommended (Arranz et al, 2012; O’Keefe et al, 2007). Grape berries and juice contain free volatile and bound non-volatile compounds (metabolites) which are responsible for the primary sensory attributes of the cultivar (Robinson et al, 2014; Swiegers et al, 2005). The wine yeast strain (starter culture) used for alcoholic fermentation contributes to varietal aroma and flavour by converting the non-volatile bound compounds i.e. thiols namely 4-mercapto4-methyl-2-pentanone (4MMP), 3-mercapto-1hexanol (3MH) 3-mercapto-hexyl acetate (3MHA) present in the grape berries and juice to aromatic volatile thiols during fermentation. Volatile thiols are considered varietal impact aroma compounds of, especially Sauvignon blanc due to the characteristic tropical fruit aroma and flavours it brings about in this cultivar (Coetzee and Du Toit, 2012; Tominaga et al, 2003). Wine sensory characteristics originate from grapederived metabolites (Ebeler and Thorngate, 2009; González-Barreiro et al, 2015), yeast-synthesised and yeast-released metabolites (Bartowsky and Pretorius, 2009; Hart et al, 2017)

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Discussion

Conclusion