Wine Yeasts Selection: Laboratory Characterization and Protocol Review

Wine aroma modification by Hanseniaspora uvarum: A multiple-step strategy for screening potential mixed starters

Hanseniaspora uvarum is a prevalent yeast species in vineyards. However, its application in grape wine fermentation remains limited. This study used culture-dependent and -independent approaches to investigate the dynamics of H. uvarum during the spontaneous fermentation of Cabernet Sauvignon grapes. The results revealed that H. uvarum constituted 77.49 % of the non-Saccharomyces yeast population during fermentation. An indigenous strain, QTX-C10, was isolated from the 148 H. uvarum strains using a multistep screening strategy. The 1:1 co-inoculation of QTX-C10 with Saccharomyces cerevisiae proved to be an optimal strategy for mixed fermentation, resulting in a 48.54 %-59.55 % increase in ethyl esters in Cabernet Sauvignon wine and a 96.94 %-110.92 % increase in Chardonnay wine. Furthermore, this approach reduced the acetic acid levels by 12.50 %-17.07 % for Cabernet Sauvignon wine and 10.81 %-17.78 % for Chardonnay wine. Additionally, increased ethyl ester content may enhance the tropical fruit flavor of Cabernet Sauvignon wines.

Developing a novel selection method for alcoholic fermentation starters by exploring wine yeast microbiota from Greece

The selection of native yeast for alcoholic fermentation in wine focuses on ensuring the success of the process and promoting the quality of the final product. The purpose of this study was firstly to create a large collection of new yeast isolates and categorize them based on their oenological potential. Additionally, the geographical distribution of the most dominant species, Saccharomyces cerevisiae, was further explored. Towards this direction, fourteen spontaneously fermented wines from different regions of Greece were collected for yeast typing. The yeast isolates were subjected in molecular analyses and identification at species level. RAPD (Random Amplified Polymorphic DNA) genomic fingerprinting with the oligo-nucleotide primer M13 was used, combined with Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) technique. All yeast isolates were scrutinized for their sensitivity to killer toxin, production of non-desirable metabolites such as acetic acid and H2S, β-glucosidase production and resistance to the antimicrobial agent; SO2. In parallel, S. cerevisiae isolates were typed at strain level by interdelta - PCR genomic fingerprinting. S. cerevisiae strains were examined for their fermentative capacity in laboratory scale fermentation on pasteurized grape must. Glucose and fructose consumption was monitored daily and at the final point a free sorting task was conducted to categorize the samples according to their organoleptic profile. According to our results, among the 190 isolates, S. cerevisiae was the most dominant species while some less common non-Saccharomyces species such as Trigonopsis californica, Priceomyces carsonii, Zygosaccharomyces bailii, Brettanomyces bruxellensis and Pichia manshurica were identified in minor abundancies. According to phenotypic typing, most isolates were neutral to killer toxin test and exhibited low acetic acid production. Hierarchical Cluster Analysis revealed the presence of four yeast groups based on phenotypic fingerprinting. Strain level typing reported 20 different S. cerevisiae strains from which 65% indicated fermentative capacity and led to dry wines. Sensory evaluation results clearly discriminated the produced wines and consequently, the proposed yeast categorization was confirmed. A novel approach that employs biostatistical tools for a rapid screening and classification of indigenous wine yeasts with oenological potential, allowing a more efficient preliminary selection or rejection of isolates is proposed.

Survey of the yeast ecology of dehydrated grapes and strain selection for wine fermentation

In this study we investigated the yeast population present on partially dehydrated Nebbiolo grapes destined for 'Sforzato di Valtellina', with the aim to select indigenous starters suitable for the production of this wine. Yeasts were enumerated, isolated, and identified by molecular methods (5.8S-ITS-RFLP and D1/D2 domain sequencing). A genetic, physiological (ethanol and sulphur dioxide tolerance, potentially useful enzymatic activities, hydrogen sulphide production, adhesive properties, and killer activity) and oenological (laboratory pure micro-fermentations) characterization was also carried out. Based on relevant physiological features, seven non-Saccharomyces strains were chosen for laboratory-scale fermentations, either in pure or in mixed-culture (simultaneous and sequential inoculum) with a commercial Saccharomyces cerevisiae strain. Finally, the best couples and inoculation strategy were further tested in mixed fermentations in winery. In both laboratory and winery, microbiological and chemical analyses were conducted during fermentation. The most abundant species on grapes were Hanseniaspora uvarum (27.4 % of the isolates), followed by Metschnikowia spp. (21.0 %) and Starmerella bacillaris (12.9 %). Technological characterization highlighted several inter- and intra-species differences. The best oenological aptitude was highlighted for species Starm. bacillaris, Metschnikowia spp., Pichia kluyveri and Zygosaccharomyces bailli. The best fermentation performances in laboratory-scale fermentations were found for Starm. bacillaris and P. kluyveri, due to their ability to reduce ethanol (-0.34 % v/v) and enhance glycerol production (+0.46 g/L). This behavior was further confirmed in winery. Results of this study contribute to the knowledge of yeast communities associated with a specific environment, like those of Valtellina wine region.

Screening of Saccharomyces and Non-Saccharomyces Wine Yeasts for Their Decarboxylase Activity of Amino Acids

The type and quantity of precursor amino acids present in grape must that are used by wine yeasts affect the organoleptic and health properties of wine. The aim of this work was to conduct a preliminary screening among Saccharomyces and non-Saccharomyces indigenous strains, which were previously isolated from different Italian regional grape varieties. This was performed in order to evaluate their decarboxylase activity on certain important amino acids-such as arginine, proline, serine, and tyrosine-that are present in grape must. In particular, a qualitative test on 122 wine yeasts was performed on a decarboxylase medium using arginine, proline, serine, and tyrosine as precursor amino acids. Our results showed a considerable variability among the microbial species tested for this parameter. Indeed, Saccharomyces cerevisiae strains exhibited a high decarboxylase capability of the four amino acids tested; moreover, only 10% of the total (i.e., a total of 81) did not show this trait. A high recovery of decarboxylation ability for at least one amino acid was also found for Zygosaccharomyces bailii and Hanseniaspora spp. These findings can, therefore, promote the inclusion of decarboxylase activity as an additional characteristic in a wine yeast selection program in order to choose starter cultures that possess desirable technological traits; moreover, this also can contribute to the safeguarding of consumer health.

Exploring Use of the Metschnikowia pulcherrima Clade to Improve Properties of Fruit Wines

Mixed fermentation using Saccharomyces cerevisiae and non-Saccharomyces yeasts as starter cultures is well known to improve the complexity of wines and accentuate their characteristics. This study examines the use of controlled mixed fermentations with the Metschnikowia pulcherrima clade, Saccharomyces cerevisiae Tokay, and non-conventional yeasts: Wickerhamomyces anomalus and Dekkera bruxellensis. We investigated the assimilation profiles, enzyme fingerprinting, and metabolic profiles of yeast species, both individually and in mixed systems. The chemical complexity of apple wines was improved using the M. pulcherrima clade as co-starters. M. pulcherrima with S. cerevisiae produced a wine with a lower ethanol content, similar glycerol level, and a higher level of volatilome. However, inoculation with the Dekkera and Wickerhamomyces strains may slightly reduce this effect. The final beneficial effect of co-fermentation with M. pulcherrima may also depend on the type of fruit must.