Effect of must characteristics on the diversity of Saccharomyces strains and their prevalence in spontaneous fermentations

Opportunities and Challenges of Understanding Community Assembly in Spontaneous Food Fermentation

Spontaneous fermentations that do not rely on backslopping or industrial starter cultures were especially important to the early development of society and are still practiced around the world today. While current literature on spontaneous fermentations is observational and descriptive, it is important to understand the underlying mechanism of microbial community assembly and how this correlates with changes observed in microbial succession, composition, interaction, and metabolite production. Spontaneous food and beverage fermentations are home to autochthonous bacteria and fungi that are naturally inoculated from raw materials, environment, and equipment. This review discusses the factors that play an important role in microbial community assembly, particularly focusing on commonly reported yeasts and bacteria isolated from spontaneously fermenting food and beverages, and how this affects the fermentation dynamics. A wide range of studies have been conducted in spontaneously fermented foods that highlight some of the mechanisms that are involved in microbial interactions, niche adaptation, and lifestyle of these microorganisms. Moreover, we will also highlight how controlled culture experiments provide greater insight into understanding microbial interactions, a modest attempt in decoding the complexity of spontaneous fermentations. Further research using specific in vitro microbial models to understand the role of core microbiota are needed to fill the knowledge gap that currently exists in understanding how the phenotypic and genotypic expression of these microorganisms aid in their successful adaptation and shape fermentation outcomes. Furthermore, there is still a vast opportunity to understand strain level implications on community assembly. Translating these findings will also help in improving other fermentation systems to help gain more control over the fermentation process and maintain consistent and superior product quality.

Biodiversity and oenological attitude of Saccharomyces cerevisiae strains isolated in the Montalcino district: biodiversity of S. cerevisiae strains of Montalcino wines

The biodiversity of Saccharomyces cerevisiae was studied in the Montalcino area (Italy). Two wineries were involved in the study, which compared the genotypic and oenological characteristics of the S. cerevisiae strains isolated in spontaneous fermentations. After isolation yeasts were identified by 26S rRNA gene sequence analysis, and S. cerevisiae strains were characterized through interdelta sequence analysis (ISA). Oenological tests were performed in synthetic grape must by varying the magnitude of the main wine-imiting factors. The evolution of alcoholic fermentation was monitored by measuring sugar consumption and flow cytometry. The results revealed the prevalence of S. cerevisiae from the third day of fermentation and the presence of a wide range of S. cerevisiae strains having ISA profiles characteristic of each winery. From an oenological point of view, the features of such strains, in terms of resistance to wine-limiting factors, seemed to be linked to the main oenological variables applied in the production process of each winery. Extreme fermentation temperatures and copper residues are the variables that mostly depress the yeast population, in terms of fermentation rate and cell viability. Flow cytometry revealed the different impact of limiting factors on the viability of yeast by the quantification of the ratio between live/dead yeast cells of each strain, suggesting different mechanisms of inhibition, for instance stuck of cell growth or cell killing, in response to the different stress factors.

Application of Autochthonous Yeast Saccharomyces cerevisiae XG3 in Treixadura Wines from D.O. Ribeiro (NW Spain): Effect on Wine Aroma

Yeast plays an essential role in winemaking. Saccharomyces cerevisiae strains involved in fermentation determine the chemical and sensory characteristics of wines. S. cerevisiae XG3, isolated in Galicia (NW Spain), has desirable oenological potential, which has been proved at a pilot scale to produce quality wines. This study applies XG3 as active dry yeast at an industrial scale for Treixadura wine elaboration, and compares it with commercial yeast and spontaneous fermentation within three wineries included in Denomination of Origin Ribeiro over two vintages. Fermentations are monitored using conventional methods, and microbiological implantation controls are carried out by mtDNA-RFLPs analysis. Wine basic chemical parameters are determined using OIV official methodology, and volatile aroma compounds are determined by GC-MS. Finally, wine sensory analysis is also performed. S. cerevisiae XG3 shows an acceptable implantation ability—as compared to commercial control strains. The wines from XG3 have a higher total acidity and lower alcohol content. Their volatile composition differs from control wines, since XG3 produces significantly higher concentrations of acetates, volatile acids, esters and volatile phenols, depending on the vintage and winery. However, lower differences are perceived at the sensory level, where fruity and floral descriptors are perceived by the panellists in XG3 wines. Therefore, XG3 constitutes an alternative to differentiate Treixadura wines.

Capturing yeast associated with grapes and spontaneous fermentations of the Negro Saurí minority variety from an experimental vineyard near León

‘Microbial terroir’ relates to the influence of autochthonous yeasts associated with a grape cultivar on the resultant wine. Geographic region, vineyard site and topography, climate and vintage influence the biodiversity of these microbial communities. Current research focus attempts to correlate their ‘microbial fingerprint’ to the sensorial and chemical characteristics of varietal wines from distinct geographical wine regions. This study focuses on the minor red grape variety, Negro Saurí, which has seen a resurgence in the León Appellation of Origin in Spain as a varietal wine. An experimental vineyard at Melgarajo S.A. (42° 15′ 48.68_N 5° 9′ 56.66_W) was sampled over four consecutive vintages, with autochthonous yeasts being isolated from grapes, must and pilot-scale un-inoculated fermentations, and identified by ITS sequencing. Forty-nine isolates belonging to Metschnikowia pulcherrima, Lachancea thermotolerans, Hanseniaspora uvarum and Torulaspora delbrueckii were isolated from grapes and must, and early stages of fermentation dependent on seasonal variation. Saccharomyces cerevisiae predominated throughout fermentation, as a heterogeneous and dynamic population, with seven major biotypes identified amongst 110 isolates across four consecutive vintages. Twenty-four S. cerevisiae isolates representing five strains dominated in two or more vintages. Their persistence through fermentation warrants further validation of their oenological properties as starter cultures.

An indigenous Saccharomyces uvarum population with high genetic diversity dominates uninoculated Chardonnay fermentations at a Canadian winery

Saccharomyces cerevisiae is the primary yeast species responsible for most fermentations in winemaking. However, other yeasts, including Saccharomyces uvarum, have occasionally been found conducting commercial fermentations around the world. S. uvarum is typically associated with white wine fermentations in cool-climate wine regions, and has been identified as the dominant yeast in fermentations from France, Hungary, northern Italy, and, recently, Canada. However, little is known about how the origin and genetic diversity of the Canadian S. uvarum population relates to strains from other parts of the world. In this study, a highly diverse S. uvarum population was found dominating uninoculated commercial fermentations of Chardonnay grapes sourced from two different vineyards. Most of the strains identified were found to be genetically distinct from S. uvarum strains isolated globally. Of the 106 strains of S. uvarum identified in this study, four played a dominant role in the fermentations, with some strains predominating in the fermentations from one vineyard over the other. Furthermore, two of these dominant strains were previously identified as dominant strains in uninoculated Chardonnay fermentations at the same winery two years earlier, suggesting the presence of a winery-resident population of indigenous S. uvarum. This research provides valuable insight into the diversity and persistence of non-commercial S. uvarum strains in North America, and a stepping stone for future work into the enological potential of an alternative Saccharomyces yeast species.

Saccharomyces cerevisiae Strain Diversity Associated with Spontaneous Fermentations in Organic Wineries from Galicia (NW Spain)

Yeast play an essential role in wine quality. The dynamics of yeast strains during fermentation determine the final chemical and sensory characteristics of wines. This study aims to evaluate the Saccharomyces cerevisiae strains diversity in organic wineries from Galicia (NW Spain). Samples from spontaneous fermentations were taken in five wineries over three consecutive years (2013 to 2015). The samples were transported to the laboratory and processed following standard methodology for yeast isolation. S. cerevisiae strains were differentiated by mDNA-RFLPs. A total of 66 different strains were identified. Some of them presented a wide distribution and appeared in several wineries. However, other strains were typical from a specific winery. Similarity analysis using two different statistical tests showed significant differences in strain diversity among wineries. The results also revealed high biodiversity indexes; however, only some strains showed an important incidence in their distribution and frequency. Our findings confirmed that spontaneous fermentation favored the existence of a high S. cerevisiae strain diversity in organic wineries from Galicia. The presence of different yeasts during fermentation, specially winery-specific strains, contribute to increased wine complexity and differentiation.

The impact of active dry yeasts in commercial wineries from the Denomination of Origen "Vinos de Madrid", Spain

This paper has studied the success of implantation for 16 commercial active dry yeasts (ADYs) during industrial fermentation (30) and the impact of these yeasts during spontaneous fermentations (19) in 10 wineries from the Denomination of Origin "Vinos de Madrid" over two consecutive years. Yeasts strains were identified by molecular techniques, pulsed field electrophoresis and microsatellite analysis. According to these techniques, all the ADYs were different with the exceptions of two strains, L2056 and Rh, which showed the same karyotype and loci size. The results showed that inoculating fermentations with ADYs did not ensure their dominance throughout the fermentation; the implantation level of ADYs was above 80% in only 9 of the 30 commercial fermentations studied; while in 16 fermentations, the dominance of the inoculated ADYs was below 50%. The type of vinification with the best implantation results overall were those associated with red wine fermentations. ADYs affected spontaneous fermentations, although their impact was observed to decrease in the second year of the study. Therefore, specific adaptation studies are necessary before using commercial yeasts during the fermentation process. At the same time, a study was carried out on the frequency of commercial strains in IMIDRA's yeast collection, made up of strains isolated from spontaneous fermentations of the different areas and cellars since the beginning of the Denomination of Origin "Vinos de Madrid" in 1990. Six different ADYs were found with a frequency of less than 5%.

The Different Physical and Chemical Composition of Grape Juice and Marc Influence Saccharomyces cerevisiae Strains Distribution During Fermentation

During white-grape winemaking, grape marc is separated from juice immediately after crushing. Both mark and juice are obtained from the same grapes, but they differ strongly for their physical and chemical properties. Marc is mainly composed of solid residues. Its pH is usually higher than that of the juice and Saccharomyces cerevisiae strains are largely present. Therefore, it can be considered as a potential alternative environment for the selection of industrial yeasts. In order to evaluate the effect of different pH and physical state of the two matrices on grapes yeast population composition, the isolation of S. cerevisiae, from both grape juice and marc during simultaneous fermentations, was performed. After yeast identification and genotyping, strains present at high frequencies were tested in fermentation at different pH values. Biofilm production was also tested to evaluate strain ability to develop on a solid matrix. Genotype analysis showed that high-frequency strains were always more abundant in one of the two environments, suggesting the existence of a selective effect. Generally, fermentations at different pH revealed that the best fermentation performance of each strain, in terms of CO₂ production, was in the pH range of its original environment. Only one strain, mostly present in grape marc, produced a high biofilm level. Therefore, biofilm production does not seem to favor strain adaptation to grape marc condition.

PRACTICAL APPLICATION

These results demonstrate that grape juice and marc represent two different environments able to influence yeast strains distribution. The pH level can be included among the selection factors acting on yeast strains distribution. Grape marc can be considered a yeasts reservoir and its fermentation can be used for the development and isolation of new strains, genetically and physiologically different from those present in the grape juice.

Past and Future of Non-Saccharomyces Yeasts: From Spoilage Microorganisms to Biotechnological Tools for Improving Wine Aroma Complexity

It is well established that non-Saccharomyces wine yeasts, considered in the past as undesired or spoilage yeasts, can enhance the analytical composition, and aroma profile of the wine. The contribution of non-Saccharomyces yeasts, including the ability to secret enzymes and produce secondary metabolites, glycerol and ethanol, release of mannoproteins or contributions to color stability, is species- and strain-specific, pointing out the key importance of a clever strain selection. The use of mixed starters of selected non-Saccharomyces yeasts with strains of Saccharomyces cerevisiae represents an alternative to both spontaneous and inoculated wine fermentations, taking advantage of the potential positive role that non-Saccharomyces wine yeast species play in the organoleptic characteristics of wine. In this context mixed starters can meet the growing demand for new and improved wine yeast strains adapted to different types and styles of wine. With the aim of presenting old and new evidences on the potential of non-Saccharomyces yeasts to address this market trend, we mainly review the studies focused on non-Saccharomyces strain selection and design of mixed starters directed to improve primary and secondary aroma of wines. The ability of non-Saccharomyces wine yeasts to produce enzymes and metabolites of oenological relevance is also discussed.

Implantation and persistence of yeast inoculum in Pinot noir fermentations at three Canadian wineries

Inoculated fermentations are practiced in most wine regions of the world. This type of fermentation involves adding a commercial Saccharomyces cerevisiae strain as an inoculant. It is often assumed that the inoculant maintains dominance throughout the fermentation; however, sometimes commercial or indigenous yeasts, which were not intentionally added, end up as the dominant yeast in the winery fermentation. The aim of this study was to compare implantation/persistence of inoculants among three Canadian wineries (Quails' Gate, Cedar Creek, and Road 13 wineries). In 2010, three inoculated fermentation tanks at each of three wineries were sampled at four stages of fermentation (pre-inoculation, early, mid, and end). In addition, results from the end stage of fermentation, from two of the three wineries, were compared among different vintages (resulting in a 4-year comparison at Quails' Gate winery and a 2-year comparison at Cedar Creek winery). Strains of S. cerevisiae were discriminated by microsatellite analysis and identified using commercial microsatellite databases, whereas DNA sequencing was used to identify non-Saccharomyces. The percent implantation/persistence of the inoculum was significantly lower at Quails' Gate and Cedar Creek wineries as compared with the Road 13 winery in the 2010 vintage. Relatively low persistence of the inoculum at Quails' Gate winery was also found in the 2009 vintage, but low values were not found at Quails' Gate winery in 2011 and 2012 or at Cedar Creek winery in 2012. In all tanks having <80% relative abundance of the inoculant, the commercial strain (Lalvin ICV-D254®/Fermol® Premier Cru) was the dominant or co-dominant yeast. Our findings highlight year-to-year variation in inoculum implantation/persistence and the idea that unless strain typing of S. cerevisiae is conducted at the winery, there are no obvious fermentation factors that would indicate a relatively low inoculum implantation/persistence.

Identification of indigenous yeast flora isolated from the five winegrape varieties harvested in Xiangning, China

Inoculated fermentation by selected indigenous yeast strains from a specific location could provide the wine with unique regional sensory characteristics. The identification and differentiation of local yeasts are the first step to understand the function of yeasts and develop a better strain-selection program for winemaking. The indigenous yeasts in five grape varieties, Chardonnay, Cabernet Franc, Cabernet Sauvignon, Marselan, and Merlot cultivated in Xiangning, Shanxi, China were investigated. Eight species of seven genera including Aureobasidium pullulans, Candida zemplinina, Hanseniaspora uvarum, Hanseniaspora occidentalis, Issatchenkia terricola, Metschnikowia pulcherrima, Pichia kluyveri, and Saccharomyces cerevisiae were identified using Wallerstein Laboratory Nutrient medium with sequencing of the 26S rDNA D1/D2 domain. H. uvarum and S. cerevisiae were the predominant species, while most non-Saccharomyces species were present in the whole fermentation process at different levels among the grape varieties. The genotypes of S. cerevisiae from each microvinification were determined by using interdelta sequence analysis. The 102 isolates showed eight different genotypes, and genotype III was the predominant genotype found. The distribution of S. cerevisiae strains during the fermentation of Marselan was also studied. Six genotypes were observed among the 92 strains with different genotypes of competitiveness at different sampling stages. Genotype V demonstrated the potential for organizing starter strains and avoiding inefficient fermentation. In general, this study explored the yeast species in the grapes grown in Xiangning County and provided important information of relationship of local yeast diversity and its regional wine sensory characteristics.