Effect of non-wine Saccharomyces yeasts and bottle aging on the release and generation of aromas in semi-synthetic Tempranillo wines

Impact of non-Saccharomyces yeasts derived from traditional fermented foods on beer aroma: Analysis based on HS-SPME-GC/MS combined with chemometrics

In recent years, numerous studies have demonstrated the significant potential of non-Saccharomyces yeasts in aroma generation during fermentation. In this study, 134 strains of yeast were isolated from traditional fermented foods. Subsequently, through primary and tertiary screening, 28 strains of aroma-producing non-Saccharomyces yeast were selected for beer brewing. Headspace-solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and chemometrics were employed to analyze the volatile flavor substances in beer samples fermented using these strains. Chemometric analysis revealed that distinct species of non-Saccharomyces yeast had a unique influence on beer aroma, with strains from the same genus producing more similar flavor profiles. Accordingly, 2,6-nonadienal, 1-pentanol, phenyl ethanol, isoamyl acetate, ethyl caprate, butyl butyrate, ethyl propionate, furfuryl alcohol, phenethyl acetate, ethyl butyrate, ethyl laurate, acetic acid, and 3-methyl-4 heptanone were identified as the key aroma compounds for distinguishing among different non-Saccharomyces yeast species. This work provides useful insights into the aroma-producing characteristics of different non-Saccharomyces yeasts to reference the targeted improvement of beer aroma.

Targeted 1-H-NMR wine analyses revealed specific metabolomic signatures of yeast populations belonging to the Saccharomyces genus

This study aimed to explore the non-volatile metabolomic variability of a large panel of strains (44) belonging to the Saccharomyces cerevisiae and Saccharomyces uvarum species in the context of the wine alcoholic fermentation. For the S. cerevisiae strains flor, fruit and wine strains isolated from different anthropic niches were compared. This phenotypic survey was achieved with a special focus on acidity management by using natural grape juices showing opposite level of acidity. A 1H NMR based metabolomics approach was developed for quantifying fifteen wine metabolites that showed important quantitative variability within the strains. Thanks to the robustness of the assay and the low amount of sample required, this tool is relevant for the analysis of the metabolomic profile of numerous wines. The S. cerevisiae and S. uvarum species displayed significant differences for malic, succinic, and pyruvic acids, as well as for glycerol and 2,3-butanediol production. As expected, S. uvarum showed weaker fermentation fitness but interesting acidifying properties. The three groups of S. cerevisiae strains showed different metabolic profiles mostly related to their production and consumption of organic acids. More specifically, flor yeast consumed more malic acid and produced more acetic acid than the other S. cerevisiae strains which was never reported before. These features might be linked to the ability of flor yeasts to shift their metabolism during wine oxidation.

Presence of Saccharomyces eubayanus in fermentative environments reveals a new adaptive scenario in Patagonia

Patagonia (Argentina and Chile) harbors the highest Saccharomyces eubayanus genomic diversity and its widest predominance in natural environments. In this work, S. eubayanus was isolated for the first time from a fermentative environment. This species was found dominating both a traditional apple chicha fermentation as well as feral apple trees in the Andean region of Aluminé (Argentina). S. eubayanus was the only Saccharomyces species found in the isolation substrates, although it coexisted with other non-Saccharomyces species. The absence of strong fermentative competitors of the Saccharomyces genus (like Saccharomyces uvarum or Saccharomyces cerevisiae) in the feral apples could promote the development and implantation of S. eubayanus in a spontaneous apple must fermentation. Phylogeographic analyses revealed a high intraspecific diversity in S. eubayanus, enabling the characterization of strains belonging to the genomic subpopulations PA1, PA2, and PB1 according to the sequences obtained for the intFR gene region. This result evidence that the studied sampling area represents a natural habitat for the species. Being a novel finding, studying the causes that allowed this species to prosper in a fermentative environment becomes essential. Hence, the physiological profile of the new isolates, including their ability to grow at different temperature, nitrogen, and ethanol concentrations was evaluated in comparison with a set of S. eubayanus strains previously isolated from natural environment and representing different genomic subpopulations. Greater physiological diversity was evidenced when strains isolated from both natural and fermentative environments were analyzed overall. Furthermore, no direct relationship between genomic population and physiological behavior was observed; on the opposite, strains appeared to exhibit similar behavior, primarily grouped by isolation origin.

Beyond S. cerevisiae for winemaking: Fermentation-related trait diversity in the genus Saccharomyces

Saccharomyces cerevisiae is the yeast of choice for most inoculated wine fermentations worldwide. However, many other yeast species and genera display phenotypes of interest that may help address the environmental and commercial challenges the wine industry has been facing in recent years. This work aimed to provide, for the first time, a systematic phenotyping of all Saccharomyces species under winemaking conditions. For this purpose, we characterized the fermentative and metabolic properties of 92 Saccharomyces strains in synthetic grape must at two different temperatures. The fermentative potential of alternative yeasts was higher than expected, as nearly all strains were able to complete fermentation, in some cases more efficiently than commercial S. cerevisiae strains. Various species showed interesting metabolic traits, such as high glycerol, succinate and odour-active compound production, or low acetic acid production, compared to S. cerevisiae. Altogether, these results reveal that non-cerevisiae Saccharomyces yeasts are especially interesting for wine fermentation, as they may offer advantages over both S. cerevisiae and non-Saccharomyces strains. This study highlights the potential of alternative Saccharomyces species for winemaking, paving the way for further research and, potentially, for their industrial exploitation.

Identification and assessment of non-conventional yeasts in mixed fermentations for brewing bioflavored beer

The increasing demand for more flavored and complex beers encourages the investigation of novel and non-conventional yeasts with the ability to provide a combination of bioflavoring and low ethanol yields. The present study identified 22 yeasts isolated from different brewing sources, including the fermentation by-products known as yeast sludges, and characterized a selection of strains to find the more suitable for the aforementioned aims. HPLC and GC-FID analysis of its brewing products were performed. The most promising results were obtained with the non-conventional yeasts Pichia kudriavzevii MBELGA61 and Meyerozyma guilliermondii MUS122. The former, isolated from a Belgian wheat beer sludge, was capable of growing in wort (17.0°Bx., 20 °C) with very low ethanol yields (1.19 % v/v). Besides, upon mixed fermentations with Saccharomyces cerevisiae, was suitable to produce volatile compounds such as ethyl acetate, 2-phenyl ethanol and isoamyl alcohol, with characteristic fruity notes. M. guilliermondii MUS122, isolated from a golden ale beer sludge, partially attenuated the wort with low production of ethanol and biomass. In addition, provided some fruity and floral nuances to the aroma profile of mixed fermentations with brewer's yeast. The results suggest that these strains favor the development of more fruity-flowery aroma profiles in beers. Furthermore, they are suitable for use in mixed fermentations with Saccharomyces brewer's strains, although the ethanol level did not decrease significantly.

Generation of intra- and interspecific Saccharomyces hybrids with improved oenological and aromatic properties

Non-wine yeasts could enhance the aroma and organoleptic profile of wines. However, compared to wine strains, they have specific intolerances to winemaking conditions. To solve this problem, we generated intra- and interspecific hybrids using a non-GMO technique (rare-mating) in which non-wine strains of S. uvarum, S. kudriavzevii and S. cerevisiae species were crossed with a wine S. cerevisiae yeast. The hybrid that inherited the wine yeast mitochondrial showed better fermentation capacities, whereas hybrids carrying the non-wine strain mitotype reduced ethanol levels and increased glycerol, 2,3-butanediol and organic acid production. Moreover, all the hybrids produced several fruity and floral aromas compared to the wine yeast: β-phenylethyl acetate, isobutyl acetate, γ-octalactone, ethyl cinnamate in both varietal wines. Sc × Sk crosses produced three- to sixfold higher polyfunctional mercaptans, 4-mercapto-4-methylpentan-2-one (4MMP) and 3-mercaptohexanol (3MH). We proposed that the exceptional 3MH release observed in an S. cerevisiae × S. kudriavzevii hybrid was due to the cleavage of the non-volatile glutathione precursor (Glt-3MH) to detoxify the cell from the presence of methylglyoxal, a compound related to the high glycerol yield reached by this hybrid. In conclusion, hybrid generation allows us to obtain aromatically improved yeasts concerning their wine parent. In addition, they reduced ethanol and increased organic acids yields, which counteracts climate change effect on grapes.