Effect of pure and mixed cultures of the main wine yeast species on grape must fermentations

Influence of Vineyard Location, Cluster Thinning and Spontaneous Alcoholic Fermentation on Wine Composition

The influence of the vineyard location, the yield per vine and the type of alcoholic fermentation on the composition of Merlot wine from two consecutive vintages was investigated in a simultaneous experiment. Grapes from two locations and two crop loads per vine, from controlled and thinned vines, were vinified. At the same time, grapes from control vines were vinified with inoculated and spontaneous alcoholic fermentation. Comparisons of the wine composition were made using a targeted metabolomic approach, microbiological analysis and sensory evaluation. It has been confirmed that the composition of Merlot wine is essentially determined by the location of the vineyard. The analytical marker used to distinguish the two locations was the content of 3-mercaptohexan-1-ol (significantly higher in location B with 38-130%). It has also been shown that the type of alcoholic fermentation has a greater influence on the composition of the wine than the crop load. The analytical marker used for the cluster thinning was the pH of the wine, which increased significantly by 0.03 to 0.08 units with the lower crop load, and for the type of alcoholic fermentation, the concentration of 2-phenethyl acetate, which relates to the sum of acetates and 2-phenylethanol, which increased significantly by 58-299%, 54-218%, and 24-46% in the spontaneously fermented wines. Both the location of the vineyard and spontaneous alcoholic fermentation influenced the significant differences in the sensory characteristics of the wine, while cluster thinning had no such influence. The other influences of the two technical factors on the wine composition depended on the location of the vineyard and the vintage. It can also be concluded that spontaneous alcoholic fermentation reduced the influence of the vintage on the wine composition, while the opposite was the case with cluster thinning.

Grape-specific native microbial communities influence the volatile compound profiles in fermenting grape juices

The impact of native grape microbiota on wine identity is not completely elucidated. In this work, we explored this issue using microbial communities prepared from V. vinifera (Malbec) and V. labrusca (Isabella) grapes as starters for the fermentation of Malbec grape juice. Analyses of early-stage reconstituted homologous and heterologous fermentations revealed that each Vitis-specific microbial starter influenced the volatile profiles of the resulting fermented grape juice. Changes in the relative abundance of the three main non-Saccharomyces yeast species identified (Hanseniaspora uvarum, Hanseniaspora opuntiae, and Starmerella bacillaris) were observed throughout these fermentations, which could explain the differences in their volatile profiles. Growth parameters determined for yeast isolates from these species, obtained from the Isabella and Malbec microbiotas, showed no growth differences in either Malbec or Isabella grape juices. Our findings support the notion that Vitis-specific microbial communities play a critical role in shaping the identity of grape juice fermentations.

Enhancing variety aromatic characteristics of Muscat wine through cold maceration with indigenous cryotolerant Metschnikowia pulcherrima Mp0520

Cold maceration (CM) is widely applied in winemaking to improve wine aroma and overall quality. However, more efficient CM techniques for industrial-scale winemaking are still needed. This study examined the impact of CM with indigenous cryotolerant Metschnikowia pulcherrima Mp0520 (Mp-CM) on the Muscat wine aromatic characteristics. The results demonstrated a significant divergence in the types and concentrations of aroma compounds between Mp-CM wine and the control. The Mp-CM wine exhibited a significantly higher terpenes content, resulting in a Muscat wine characterized by terpenes, compared to the control predominated by esters. Additionally, the Mp-CM wine demonstrated elevated levels of α-terpineol and terpinolene, potentially enhancing the varietal aroma stability of Muscat wine. Furthermore, Mp-CM gave Muscat wine a heightened fruity aroma and a more complex aroma. These findings suggested that the Mp-CM utilized in this study offered promising avenues for enhancing the variety aroma characteristics of Muscat wine on large scale winemaking.

Improving aromatic higher alcohol acetates in wines by co-fermentation of Pichia kluyveri and Saccharomyces cerevisiae: growth interaction and amino acid competition

BACKGROUND

Higher alcohol acetates (HAAs) are potent aroma-active esters that impart desirable fruity and floral aromas. However, the conversion of higher alcohol precursors into HAAs is extremely low in winemaking. To investigate the underlying yeast-yeast interaction on targeted improvement of aromatic HAAs, we evaluated fermentation activity, cell viability, amino acid consumption and HAA production when Pichia kluyveri and Saccharomyces cerevisiae were inoculated concurrently or sequentially.

RESULTS

Pichia kluyveri PK-21 possessed the ability to survive and increased HAA level up to 5.2-fold in mixed fermentation. Such an increment may benefit from the efficient conversion of higher alcohol precursors into HAAs (>27-fold higher than S. cerevisiae). During mixed fermentation, the two yeasts exhibited crucial interactions regarding cell growth and amino acid competition. Saccharomyces cerevisiae dominated over the co-inoculated P. kluyveri by efficient uptake of amino acids and biomass production. However, this dominance decreased in sequential fermentation, where P. kluyveri growth increased due to the consumption of preferred amino acids prior to S. cerevisiae. Pearson correlation analysis indicated that phenylalanine and aspartic acid may act as positive amino acids in boosting P. kluyveri growth and HAA production. Laboratory-scale winemaking validated the fermentation performance of P. kluyveri in sequential inoculum, resulting in a balanced aroma profile with enhanced floral and tropical fruity characteristics in the final wines.

CONCLUSION

This study proposes a microbial, non-genetically engineered approach for targeted increase of HAA production in winemaking and the findings provide new insights into yeast-yeast interactions. © 2024 Society of Chemical Industry.

Exploring future applications of the apiculate yeast Hanseniaspora

As a metaphor, lemons get a bad rap; however the proverb 'if life gives you lemons, make lemonade' is often used in a motivational context. The same could be said of Hanseniaspora in winemaking. Despite its predominance in vineyards and grape must, this lemon-shaped yeast is underappreciated in terms of its contribution to the overall sensory profile of fine wine. Species belonging to this apiculate yeast are known for being common isolates not just on grape berries, but on many other fruits. They play a critical role in the early stages of a fermentation and can influence the quality of the final product. Their deliberate addition within mixed-culture fermentations shows promise in adding to the complexity of a wine and thus provide sensorial benefits. Hanseniaspora species are also key participants in the fermentations of a variety of other foodstuffs ranging from chocolate to apple cider. Outside of their role in fermentation, Hanseniaspora species have attractive biotechnological possibilities as revealed through studies on biocontrol potential, use as a whole-cell biocatalyst and important interactions with Drosophila flies. The growing amount of 'omics data on Hanseniaspora is revealing interesting features of the genus that sets it apart from the other Ascomycetes. This review collates the fields of research conducted on this apiculate yeast genus.

Application of Schizosaccharomyces japonicus in makgeolli fermentation and its brewing characteristics

Recently, unconventional yeasts have become popular as fermentation starters in the brewing industry due to the growing consumer demand for aromatic diversity. Specifically, Schizosaccharomyces japonicus has been explored as a potential starter culture for beer and wine production because of its distinct brewing characteristics; however, its application in makgeolli fermentation has not been tested. Therefore, in the present study, two Sz. japonicus strains (SZJ-1 and SZJ-2) were isolated from natural sources, and their brewing characteristics for makgeolli fermentation were compared with those of commercial S. cerevisiae strain. Although the tested isolates showed a lower fermentation and carbon source consumption rate than control-, their overall alcohol fermentation characteristics were suitable for makgeolli production. Regarding flavor composition, Sz. japonicus-fermented makgeolli possessed more ester compounds (e.g., 2-phenylethyl acetate, ethyl acetate, and ethyl decanoate) than S. cerevisiae-fermented makgeolli. Therefore, Sz. japonicus can be used as an alternative culture starter in makgeolli fermentation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01265-6.

Starmerella lactis-condensi, a yeast that has adapted to the conditions in the oenological environment

The yeast Starmerella (Candida) lactis-condensi is considered a food contaminant microorganism. The aim of our research was to determine why St. lactis-condensi could become the dominant species of Essences, the top sweet wine speciality of Tokaj wine region in Hungary. We investigated the physiological properties of these yeasts based on parameters that may influence their ability to selectively proliferate and persist during maturation in wines with very high sugar content. These include glucose and fructose, alcohol, and sulphur tolerance. Our studies have shown that St. lactis-condensi is a fructophilic yeast that is able to adapt quickly to very high sugar concentrations (up to 500 g/L) in the Essences. The high glucose concentration inhibits its growth, as well as that of the St. bacillaris (Candida zemplinina) strains tested. The type and amount of sugars in the Essences, together with the sulphur and alcohol content, influence the composition of the dominant yeast biota. Analysis of (GTG)₅ microsatellite in the nuclear genome and mtDNA-RFLP studies demonstrate that a diverse population of St. lactis-condensi occurs in the Tokaj wine region, in the Essences. This yeast species is characterised by both physiological and genetic biodiversity. GC-MS analysis of Essences colonised exclusively with these yeasts showed no deterioration in quality.

Enological Suitability of Indigenous Yeast Strains for 'Verdejo' Wine Production

The use of indigenous yeasts for the production of wines is a tool to defend the typicity of a particular region. The selection of appropriate indigenous yeasts ensures the maintenance of oenological characteristics by simulating spontaneous alcoholic fermentation (AF) while avoiding the risks of stuck or sluggish fermentations. In this study, autochthonous yeasts from Verdejo grape juice (Appellation of Origin Rueda) were selected, identified, and characterized to exploit the characteristics of the 'terroir'. The fermentation capacity of seven strains was studied individually at the laboratory scale. The most suitable strains (Saccharomyces cerevisiae: Sacch 1, Sacch 2, Sacch 4, and Sacch 6) and Sacch 6 co-inoculated with Metschnikowia pulcherrima were characterized at the pilot scale. The fermentation kinetics, bioproduct release, volatile composition, and sensory profile of the wines were evaluated. Significant differences were found, especially in the aroma profile. In particular, Sacch 6 and Sacch 6 co-inoculated with M. pulcherrima produced higher amounts of ethyl esters and acetates and lower amounts of higher alcohols than the spontaneous AF. Wines inoculated with indigenous yeasts had higher sensory scores for fruit aromas and overall rating. The selection of indigenous yeasts improved the aroma of Verdejo wines and could contribute to determining the wine typicity of the wine region.

Oenological characteristics of two indigenous Starmerella bacillaris strains isolated from Chinese wine regions

To broaden knowledge about the oenological characteristics of Starmerella bacillaris, the influence of two Chinese indigenous S. bacillaris strains on the conventional enological parameters and volatile compounds of Cabernet Sauvignon wines were investigated under different inoculation protocols (single inoculation and simultaneous/sequential inoculation with the commercial Saccharomyces cerevisiae EC1118). The results showed that the two S. bacillaris strains could complete alcohol fermentation alone under high sugar concentrations while increasing the content of glycerol and decreasing the content of acetic acid. Compared with wines fermented by EC1118 single inoculation, S. bacillaris single inoculation and S. bacillaris/EC1118 sequential inoculation increased the contents of isobutanol, ethyl isobutanoate, terpenes, and ketones and decreased the contents of isopentanol, phenylethyl alcohol, fatty acids, acetate esters, and total ethyl esters. Furthermore, for S. bacillaris/EC1118 simultaneous inoculation, the concentrations of ethyl esters were increased, contributing to a higher score of "floral" and "fruity" notes in agreement with sensory analysis. KEY POINTS: • S. bacillaris single and simultaneous/sequential inoculation. • Conventional enological parameters and volatile compounds were investigated. • S. bacillaris/EC1118 simultaneous fermentation increased ethyl esters.

Effects of Purified β-Glucosidases from Issatchenkia terricola, Pichia kudriavzevii, Metschnikowia pulcherrima on the Flavor Complexity and Typicality of Wines

The aim of this study was to investigate the effects of purified β-glucosidases from Issatchenkia terricola SLY-4, Pichia kudriavzevii F2-24, and Metschnikowia pulcherrima HX-13 (named as SLY-4E, F2-24E, and HX-13E, respectively) on the flavor complexity and typicality of wines. Cabernet Sauvignon wines were fermented by Saccharomycescerevisiae with the addition of SLY-4E, F2-24E, and HX-13E; the fermentation process and characteristics of wines were analyzed. The addition of SLY-4E, F2-24E, and HX-13E into must improved the contents of terpenes, higher alcohols, and esters, and decreased the contents of C6 compounds and fatty acids, which enhanced the fruity, floral, and taste aspects, reducing the unpleasant green of wines with no significant difference in their appearance. β-glucosidases from different yeast species produced different aroma compound profiles which presented different flavor and quality. F2-24EW had the best effect on flavor and quality of wine followed by SLY-4EW and HX-13EW. These research results can provide references for the use of β-glucosidases from non-Saccharomyces yeasts to improve the flavor complexity, typicality, and quality of wines.

The Impact of Indigenous Non-Saccharomyces Yeasts Inoculated Fermentations on ‘Semillon’ Icewine

The emerging low acidity in icewine grapes is becoming a major problem in producing quality icewine. Using non-Saccharomyces cerevisiae yeasts in fermentation can improve wine’s organoleptic characteristics and aromatic quality. This study evaluated two indigenous non-Saccharomyces cerevisiae yeasts, Lachancea thermotolerans (LT-2) and Torulaspora delbrueckii (TD-3), for their ability to improve the acidity and quality of ‘Semillon’ icewine. Five different inoculation schemes were implemented, including a single inoculation of S. cerevisiae (SC), L. thermotolerans (LT), and T. delbrueckii (TD); the sequential inoculation of L. thermotolerans, followed by S. cerevisiae after 6 days (L-S); and the sequential inoculation of L. thermotolerans, followed by T. delbrueckii after 6 days (L-D). The results showed that, during sequential fermentation (L-S and L-D), the presence of S. cerevisiae or T. delbrueckii slightly restrained the growth of L. thermotolerans. Single or sequential inoculation with L. thermotolerans and T. delbrueckii significantly reduced the amount of volatile acidity and increased the glycerol content. Furthermore, fermentations involving L. thermotolerans produced relevant amounts of lactic acid (2.04–2.2 g/L) without excessive deacidification of the icewines. Additionally, sequential fermentations increased the concentration of terpenes, C13-norisoprenoid compounds, and phenethyl compounds. A sensory analysis also revealed that sequentially fermented icewines (L-S and L-D) had more fruity and floral odors and aroma intensity. This study highlights the potential application of L. thermotolerans and T. delbrueckii in sequential fermentation to improve the icewine quality.

Effect of Commercial Yeast Starter Cultures on Cabernet Sauvignon Wine Aroma Compounds and Microbiota

Commercial Saccharomyces cerevisiae plays an important role in the traditional winemaking industry. In this study, the correlation of microbial community and aroma compound in the process of alcohol fermentation of Cabernet Sauvignon by four different commercial starters was investigated. The results showed that there was no significant difference in the fermentation parameters of the four starters, but there were differences in microbial diversity among the different starters. The wine samples fermented by CEC01 had higher microbial abundance. GC-MS detected a total of 58 aromatic compounds from the fermentation process by the experimental yeasts. There were 25 compounds in the F6d variant, which was higher than in other samples. The PCA score plot showed that 796 and F15 yeast-fermented wines had similar aromatic characteristic compositions. According to partial least squares (PLS, VIP > 1.0) analysis and Spearman’s correlation analysis, 11, 8, 8 and 10 microbial genera were identified as core microorganisms in the fermentation of 796, CEC01, CECA and F15 starter, respectively. Among them, Leuconostoc, Lactobacillus, Sphingomonas and Pseudomonas played an important role in the formation of aroma compounds such as Ethyl caprylate, Ethyl caprate and Ethyl-9-decenoate. These results can help us to have a better understanding of the effects of microorganisms on wine aroma and provide a theoretical basis for improving the flavor quality of Cabernet Sauvignon wine.

Machine Learning Techniques Disclose the Combined Effect of Fermentation Conditions on Yeast Mixed-Culture Dynamics and Wine Quality

The use of yeast starter cultures consisting of a blend of Saccharomyces cerevisiae and non-Saccharomyces yeasts has increased in recent years as a mean to address consumers’ demands for diversified wines. However, this strategy is currently limited by the lack of a comprehensive knowledge regarding the factors that determine the balance between the yeast-yeast interactions and their responses triggered in complex environments. Our previous studies demonstrated that the strain Hanseniaspora guilliermondii UTAD222 has potential to be used as an adjunct of S. cerevisiae in the wine industry due to its positive impact on the fruity and floral character of wines. To rationalize the use of this yeast consortium, this study aims to understand the influence of production factors such as sugar and nitrogen levels, fermentation temperature, and the level of co-inoculation of H. guilliermondii UTAD222 in shaping fermentation and wine composition. For that purpose, a Central Composite experimental Design was applied to investigate the combined effects of the four factors on fermentation parameters and metabolites produced. The patterns of variation of the response variables were analyzed using machine learning methods, to describe their clustered behavior and model the evolution of each cluster depending on the experimental conditions. The innovative data analysis methodology adopted goes beyond the traditional univariate approach, being able to incorporate the modularity, heterogeneity, and hierarchy inherent to metabolic systems. In this line, this study provides preliminary data and insights, enabling the development of innovative strategies to increase the aromatic and fermentative potential of H. guilliermondii UTAD222 by modulating temperature and the availability of nitrogen and/or sugars in the medium. Furthermore, the strategy followed gathered knowledge to guide the rational development of mixed blends that can be used to obtain a particular wine style, as a function of fermentation conditions.

Oenological Characteristics of Four Non-Saccharomyces Yeast Strains With β-Glycosidase Activity

Non-Saccharomyces yeast with β-glucosidase activity might positively contribute to the flavor and quality of wines. The contribution of four non-Saccharomyces yeast strains Issatchenkia terricola SLY-4, Pichia kudriavzevii F2-24, P. kudriavzevii F2-16, and Metschnikowia pulcherrima HX-13 with β-glucosidase activity to the flavor and quality of wine making was studied. Compared with those of S. cerevisiae single fermentation, the four non-Saccharomyces yeast strains could grow and consume sugar completely with longer fermentation periods, and with no significantly negative effect on chemical characteristics of wines. Moreover, they produced lower content of C6 compounds, benzene derivative, and fatty acid ethyl ester compounds and higher content of terpene, β-ionone, higher alcohol, and acetate compounds. Different yeast strains produced different aroma compounds profiles. In general, the sensory evaluation score of adding non-Saccharomyces yeast-fermented wine was better than that of S. cerevisiae, and I. terricola SLY-4 fermentation received the highest one, followed by P. kudriavzevii F2-24, P. kudriavzevii F2-16, and M. pulcherrima HX-13 from high to low. The research results provide a theoretical basis for the breeding of non-Saccharomyces yeast and its application in wine making.

Elucidating the interaction of carbon, nitrogen, and temperature on the biosynthesis of Aureobasidium pullulans antifungal volatiles

The combined biochemical impact of carbon, nitrogen and temperature on the biosynthesis of the antifungal volatile organic compounds (VOCs): ethanol, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethanol produced by Aureobasidium pullulans A1 and A3 was investigated using a Box-Behnken experimental design and response surface methodology (RSM). Normalized peak areas derived from solid phase micro extraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis, indicated that initial carbon content had a significant influence on the biosynthesis of ethanol and alcohols with greater than three carbon atoms. This result suggests a dominant activity of the A. pullulans anabolic pathway to biosynthesize three higher alcohols via de novo biosynthesis of amino acids from sugar metabolism. Low concentrations of carbon (3-13 g l^-1 ) with nitrogen as both ammonium and amino acids in the growth medium resulted in a higher number of significant linear and quadratic relationships. Nitrogen availability and growth temperature had significant negative linear and quadratic correlations with VOCs biosynthesis in most instances. Isolate-dependant metabolic response was evident for all abiotic parameters tested on alcohol production. The findings of this study offer new perspectives to improve the production of key antifungal compounds by antagonists in biological control systems.

Chemical and Sensory Profiles of Merlot Wines Produced by Sequential Inoculation of Metschnikowia pulcherrima or Meyerzyma guilliermondii

Inoculation of selected non-Saccharomyces yeasts with Saccharomyces cerevisiae as means to produce Merlot wines with reduced ethanol contents was investigated. Fermentations of grape musts (25.4° Brix, pH 3.50, and 4.23 g/L titratable acidity) were conducted in stainless steel tanks inoculated with Metschnikowia pulcherrima strains P01A016 or NS-MP or Meyerozyma guilliermondii P40D002 with S. cerevisiae Syrah added after three days. After fermentation, wines with Mt. pulcherrima contained 13.8% (P01A016) or 13.9% (NS-MP) v/v ethanol, respectively, amounts which were lower than in wines with S. cerevisiae alone (14.9% v/v). Delayed inoculation of must with S. cerevisiae (day 3) or musts with My. guilliermondii contained elevated concentrations of ethyl acetate (145 and 148 mg/L, respectively), concentrations significantly higher than those with S. cerevisiae inoculated on day 0 or with either strain of Mt. pulcherrima. Descriptive sensory analysis revealed a significant effect due to panelist but not due to Mt. pulcherrima or My. guilliermondii. This research indicates the potential for commercial application of these yeasts towards the production of reduced alcohol wines but without imparting negative sensory attributes.

Yeast Interactions and Molecular Mechanisms in Wine Fermentation: A Comprehensive Review

Wine can be defined as a complex microbial ecosystem, where different microorganisms interact in the function of different biotic and abiotic factors. During natural fermentation, the effect of unpredictable interactions between microorganisms and environmental factors leads to the establishment of a complex and stable microbiota that will define the kinetics of the process and the final product. Controlled multistarter fermentation represents a microbial approach to achieve the dual purpose of having a less risky process and a distinctive final product. Indeed, the interactions evolved between microbial consortium members strongly modulate the final sensorial properties of the wine. Therefore, in well-managed mixed fermentations, the knowledge of molecular mechanisms on the basis of yeast interactions, in a well-defined ecological niche, becomes fundamental to control the winemaking process, representing a tool to achieve such objectives. In the present work, the recent development on the molecular and metabolic interactions between non-Saccharomyces and Saccharomyces yeasts in wine fermentation was reviewed. A particular focus will be reserved on molecular studies regarding the role of nutrients, the production of the main byproducts and volatile compounds, ethanol reduction, and antagonistic actions for biological control in mixed fermentations.

Genetic, Physiological, and Industrial Aspects of the Fructophilic Non-Saccharomyces Yeast Species, Starmerella bacillaris

Starmerella bacillaris (synonym Candida zemplinina) is a non-Saccharomyces yeast species, frequently found in enological ecosystems. Peculiar aspects of the genetics and metabolism of this yeast species, as well as potential industrial applications of isolated indigenous S. bacillaris strains worldwide, have recently been explored. In this review, we summarize relevant observations from studies conducted on standard laboratory and indigenous isolated S. bacillaris strains.

Characterization of the β-Glucosidase activity in indigenous yeast isolated from wine regions in China

β-glucosidase is a pivotal enzyme that hydrolyzes bound volatile aromatic compounds. However, the activity of β-glucosidase in winemaking and the mechanism by which it affects the flavor and taste of wines have not been fully investigated. In this study, we profiled the characteristics of β-glucosidase derived from wine-related yeasts isolated from different wine-making regions in China, and analyzed the enzyme activity from different parts of the cells under aerobic and anaerobic conditions. A total of 56 strains of wine-related yeasts producing β-glucosidases were screened using the YNB-C medium (YNB 6.7 g L^-1 , cellobiose 5 g L^-1 , pH 5.0). We found that strain Clavispora lusitaniae C117 produced the highest enzyme activity (152.39 µmol pNP ml^-1 h^-1 ). In most strains, β-glucosidase were located in whole cells (periplasmic space) and permeabilized cells (intracellular). The non-Saccharomyces species had the highest enzymatic activity in a strain-dependent manner. Under aerobic conditions, C. lusitaniae C117, Hanseniaspora guilliermondii A27-3-4, Metschnikowia pulcherrima F-1-6, and Pichia anomala C84 had the highest β-glucosidase activity. We further investigated the β-glucosidase activity during the wine fermentation and the effects of sugar, pH, temperature, and ethanol on the enzyme activities of P. anomala C84 and commercial Saccharomyces yeast strains RC212 and VL1. The presence of fructose, glucose, and sucrose strongly inhibited enzyme activity. Similarly, low pH and low temperature inhibited the activity of β-glucosidase, whereas ethanol promoted enzyme activity. Our findings provide a theoretical basis on understanding the different yeast characteristics of β-glucosidase and their potential application for further improving wine aroma complexity.

Unravelling the Impact of Grape Washing, SO2, and Multi-Starter Inoculation in Lab-Scale Vinification Trials of Withered Black Grapes

Wine quality is strongly affected by chemical composition and microbial population of grape must, which, in turn, are influenced by several post-harvest treatments, including grape withering. Different strategies have been suggested to manage the fermenting must microbiota, as it plays a central role in the outcomes of both spontaneous and guided fermentations. This study aimed at evaluating the impact of grape washing, SO2 addition, and selected starter culture inoculation on population dynamics, fermentation kinetics, and main oenological parameters in lab-scale trials, focusing on withered grapes usually used for Amarone production. Although grape washing treatment was effective in removing heavy metals and undesirable microorganisms from grape berry surface, inoculation of multi-starter cultures impacted more fermentation rates. Further, both grape washing and starter inoculation procedures had a remarkable impact on wine chemical characteristics, while 30 mg/L SO2 addition did not significantly affect the fermentation process. In summary, the best strategy in terms of limiting off-flavors and potentially reducing the need for SO2 addition in wine from withered grapes was the use of yeast starters, particularly mixed cultures composed by selected strains of Metschnikowia spp. and Saccharomyces cerevisiae. Application of a washing step before winemaking showed a potential to improve organoleptic characteristics of wine.

Impacts of non-Saccharomyces species and aeration on sequential inoculation with Saccharomyces cerevisiae to produce lower alcohol Merlot wines from Washington state

BACKGROUND

Species of non-Saccharomyces yeasts isolated from Washington vineyards were evaluated for their abilities to reduce alcohol contents of wines. As many of these yeasts benefit from some oxygen, the effect of limited aeration was also studied.

RESULTS

Although fermentations of a high sugar Merlot grape must (310 g L^-1 ) did not reach dryness, inoculation of Metschnikowia chrysoperlae, Mt. pulcherrima, Meyerozyma guillermondii, Pichia kluyveri, or P. membranifaciens yielded in wines with lower amounts of ethanol without excessive levels of acetic acid. Aeration frequently resulted in wines with less ethanol but with more acetic acid compared to non-aerated fermentations. Inoculation of Mt. pulcherrima or My. guilliermondii into another Merlot grape must that contained a lower initial amount of fermentable sugar (266 g L^-1 ) resulted in dry wines that contained less alcohol.

CONCLUSIONS

Inoculation of My. guilliermondii or Mt. pulcherrima before primary alcoholic fermentation resulted in wines with reduced alcohol contents without excessive acetic acid production. © 2020 Society of Chemical Industry.

Learning from 80 years of studies: a comprehensive catalogue of non-Saccharomyces yeasts associated with viticulture and winemaking

Non-Saccharomyces yeast species are nowadays recognized for their impact on wine´s chemical composition and sensorial properties. In addition, new interest has been given to the commercial exploitation of non-Saccharomyces starter cultures in the wine sector. However, over many years, these yeast species were considered sources of contamination in wine production and conservation, mainly due to the high levels of volatile acidity obtained. The present manuscript systematizes 80 years of literature describing non-Saccharomyces yeast species isolated from grapes and/or grape musts. A link between each reference, the accepted taxonomic name of each species and their geographical occurrence is presented, compiling information for 293 species, in a total of 231 citations. One major focus of this work relates to the isolation of non-Saccharomyces yeasts from grapevines usually ignored in most sampling studies, also as isolation from damaged grapes. These particular niches are sources of specific yeast species, which are not identified in most other explored environments. These yeasts have high potential to be explored for important and diversified biotechnological applications.

Influence of Hanseniasporauvarum AS27 on Chemical and Sensorial Characteristics of Aglianico Wine

In this work was evaluated the effect of sequential inoculum of Hanseniaspora uvarum AS27 strain and a commercial Saccharomyces cerevisiae yeast on the physical–chemical and organoleptic features of Aglianico, a traditional red wine of Southern Italy. Four fermentation treatments on a pilot scale were performed. In fermentation treatment A, the alcoholic fermentation was spontaneously conducted by the indigenous yeasts present in grape must. In the fermentation treatments B and C were inoculated respectively S. cerevisiae FE and H. uvarum AS27 strains, as a single starter. The fermentation treatment D was initially inoculated with H. uvarum AS27, and S. cerevisiae strain was added after 72 h (sequential inoculation). Microbiological, physical–chemical parameters and sensory profiles of the wines have been defined. The results showed that the use of H. uvarum AS27, in sequential inoculum with S. cerevisiae FE, influenced the wine composition, enriching it in polyphenolic and volatile compounds. Further, the sensory evaluation showed that the use of H. uvarum AS27 strain, in co-culture with S. cerevisiae, gives the wine more pleasant characteristics. Therefore, the results have highlighted how the use of particular non-Saccharomyces yeasts can represent a biotechnological resource in red wine production.

The Important Contribution of Non-Saccharomyces Yeasts to the Aroma Complexity of Wine: A Review

Non-Saccharomyces yeast plays an important role in the initial stages of a wild ferment, as they are found in higher abundance in the vineyard than Saccharomyces cerevisiae. As such, there has been a focus in recent years to isolate these yeast species and characterize their effect on wine fermentation and subsequent aroma. This effect on wine aroma is often species and strain dependent, as the enzymatic profile of each yeast will determine which aroma compounds are formed as secondary metabolites. Semi-fermentative yeast, such as Hanseniaspora spp., Candida spp. and Metschnikowia pulcherrima, are commonly in high abundance in fresh grape must and have diverse enzymatic profiles, however they show a weak tolerance to ethanol, limiting their impact to the initial stages of fermentation. Fully fermentative non-Saccharomyces yeast, characterized by high ethanol tolerance, are often found at low abundance in fresh grape must, similar to Saccharomyces cerevisiae. Their ability to influence the aroma profile of wine remains high, however, due to their presence into the final stages of fermentation. Some fermentative yeasts also have unique oenological properties, such as Lanchancea thermotolerans and Schizosaccharomyces pombe, highlighting the potential of these yeast as inoculants for specific wine styles.

Mezcal as a Novel Source of Mixed Yeasts Inocula for Wine Fermentation

Mezcal yeasts were evaluated for their potential as grape-juice fermenters, characterizing their fermentation performance, both in terms of primary and volatile metabolites. Experiments were first carried-out in a semi-synthetic medium and then on grape juice, and population dynamics of the chosen mixed inoculum was assessed in grape juice. Accordingly, we initially tested 24 mezcal yeasts belonging to ten different species, and chose those that were more productive and stress tolerant for the mixed (dual) inoculum, having a final selection of three Saccharomyces cerevisiae strains (plus Fermichamp, a commercial wine strain) and three non-Saccharomyces strains, belonging to Kluyveromyces marxianus, Torulaspora delbrueckii, and Zygosaccharomyces bailii species. For the combination S. cerevisiae/T. delbrueckii (Sc/Td) mixed inoculum, we observed increasing isoamyl alcohol and phenyl ethyl acetate concentrations, as compared with the use of individual Saccharomyces strains, which resulted in a fruitier aroma profile. Alcohol final concentration was in average lower for the Sc/Td inoculum (fermentation power, FP, 13.6) as compared with the individual mezcal Saccharomyces strains (FP 14.3), and it was the highest when Td was co-cultured with the commercial strain (FP 14.6). Overall, our results show the feasibility of using yeasts isolated from mezcal as a novel source of inoculum for wine-type fermentation.

Non-Saccharomyces in Winemaking: Source of Mannoproteins, Nitrogen, Enzymes, and Antimicrobial Compounds

Traditionally, non-Saccharomyces yeasts have been considered contaminants because of their high production of metabolites with negative connotations in wine. This aspect has been changing in recent years due to an increased interest in the use of these yeasts in the winemaking process. The majority of these yeasts have a low fermentation power, being used in mixed fermentations with Saccharomyces cerevisiae due to their ability to produce metabolites of enological interest, such as glycerol, fatty acids, organic acids, esters, higher alcohols, stable pigments, among others. Additionally, existing literature reports various compounds derived from the cellular structure of non-Saccharomyces yeasts with benefits in the winemaking process, such as polysaccharides, proteins, enzymes, peptides, amino acids, or antimicrobial compounds, some of which, besides contributing to improving the quality of the wine, can be used as a source of nitrogen for the fermentation yeasts. These compounds can be produced exogenously, and later incorporated into the winemaking process, or be uptake directly by S. cerevisiae from the fermentation medium after their release via lysis of non-Saccharomyces yeasts in sequential fermentations.

Saccharomyces cerevisiae and Hanseniaspora uvarum mixed starter cultures: Influence of microbial/physical interactions on wine characteristics

The growing trend in the wine industry is the revaluation of the role of non-Saccharomyces yeasts, promoting the use of these yeasts in association with Saccharomyces cerevisiae. Non-Saccharomyces yeasts contribute to improve wine complexity and organoleptic composition. However, the use of mixed starters needs to better understand the effect of the interaction between these species during alcoholic fermentation. The aim of this study is to evaluate the influence of mixed starter cultures, composed by combination of different S. cerevisiae and Hanseniaspora uvarum strains, on wine characteristics and to investigate the role of cell-to-cell contact on the metabolites produced during alcoholic fermentation. In the first step, three H. uvarum and two S. cerevisiae strains, previously selected, were tested during mixed fermentations in natural red grape must in order to evaluate yeast population dynamics during inoculated fermentation and influence of mixed starter cultures on wine quality. One selected mixed starter was tested in a double-compartment fermentor in order to compare mixed inoculations of S. cerevisiae/H. uvarum with and without physical separation. Our results revealed that physical contact between S. cerevisiae and H. uvarum affected the viability of H. uvarum strain, influencing also the metabolic behaviour of the strains. Although different researches are available on the role of cell-to-cell contact-mediated interactions on cell viability of the strains included in the mixed starter, to our knowledge, very few studies have evaluated the influence of cell-to-cell contact on the chemical characteristics of wine.

Pilot Scale Fermentations of Sangiovese: An Overview on the Impact of Saccharomyces and Non-Saccharomyces Wine Yeasts

The production of wines with peculiar analytical and sensorial profiles, together with the microbiological control of the winemaking process, has always been one of the main objectives of the wine industry. In this perspective, the use of oenological starters containing non-Saccharomyces yeasts can represent a valid tool for achieving these objectives. Here we present the results of seven pilot scale fermentations, each of which was inoculated with a different non-Saccharomyces yeast strain and after three days with a commercial Saccharomyces cerevisiae starter. The fermentations were carried out in double on 70 L of Sangiovese grape must, the most widely planted red grape variety in Italy and particularly in Tuscany, where it is utilized for the production of more than 80% of red wines. Fermentations were monitored by assessing both the development of the microbial population and the consumption of sugars at the different sampling times. The impact of the different starters was assessed after stabilization through the evaluation of the standard analytical composition of the resulting wines, also taking into account polysaccharides and volatile compounds. Moreover, quantitative descriptive sensory analyses were carried out. Compared to the control wines obtained by inoculating the S. cerevisiae starter strain, those inoculated with non-Saccharomyces/Saccharomyces mixed starters presented a significant differentiation in the chemical-analytical composition. Moreover, sensory analysis revealed differences among wines mainly for intensity of color, astringency, and dryness mouthfeel perception.

Effects of Crude β-Glucosidases from Issatchenkia terricola, Pichia kudriavzevii, Metschnikowia pulcherrima on the Flavor Complexity and Characteristics of Wines

To investigate the effects of crude β-glucosidases from Issatchenkia terricola SLY-4 (SLY-4E), Pichia kudriavzevii F2-24 (F2-24E), and Metschnikowia pulcherrima HX-13 (HX-13E) on flavor complexity and characteristics of wines, grape juice was fermented by Saccharomyces cerevisiae with the addition of SLY-4E, F2-24E and HX-13E, respectively. The growth and sugar consumption kinetics of S. cerevisiae, the physicochemical characteristics, the volatile compounds, and the sensory dimensions of wines were analyzed. Results showed that adding SLY-4E, F2-24E, and HX-13E into must had no negative effect on the fermentation and physicochemical characteristics of wines, but increased the content of terpenes, esters, and fatty acids, while decreased the C₆ compound content. Each wine had its typical volatile compound profiles. Adding SLY-4E or F2-24E into must could significantly improve the flavor complexity and characteristics of wines. These results would provide not only an approach to improve flavor complexity and characteristics of wines, but also references for application of β-glucosidases from other sources.

Sequential Non-Saccharomyces and Saccharomyces cerevisiae Fermentations to Reduce the Alcohol Content in Wine

Over the last decades, the average alcohol content of wine has increased due to climate change and consumer preferences for particular wine styles that resulted in increased grape sugar levels at harvest. Therefore, alcohol reduction is a current challenge in the winemaking industry. Among several strategies under study, the use of non-conventional yeasts in combination with Saccharomyces cerevisiae plays an important role for lowering ethanol production in wines nowadays. In the present work, 33 native non-Saccharomyces strains were assayed in sequential culture with a S. cerevisiae wine strain to determine their potential for reducing the alcohol content in Malvar white wines. Four of the non-Saccharomyces strains (Wickerhamomyces anomalus 21A-5C, Meyerozyma guilliermondii CLI 1217, and two Metschnikowia pulcherrima (CLI 68 and CLI 460)) studied in sequential combination with S. cerevisiae CLI 889 were best able to produce dry wines with decreased alcohol proportion in comparison with one that was inoculated only with S. cerevisiae. These sequential fermentations produced wines with between 0.8% (v/v) and 1.3% (v/v) lower ethanol concentrations in Malvar wines, showing significant differences compared with the control. In addition, these combinations provided favorable oenological characteristics to wines such as high glycerol proportion, volatile higher alcohols, and esters with fruity and sweet character.

Effect of Co-Inoculation of Candida zemplinina, Saccharomyces cerevisiae and Lactobacillus plantarum for the Industrial Production of Negroamaro Wine in Apulia (Southern Italy)

The employment of multi-species starter cultures has growing importance in modern winemaking for improving the complexity and wine attributes. The assessment of compatibility for selected species/strains at the industrial-scale is crucial to assure the quality and the safety associated with fermentations. An aspect particularly relevant when the species belong to non-Saccharomyces, Saccharomyces spp. and malolactic bacteria, three categories with different biological characteristics and oenological significance. To the best of our knowledge, the present report is the first study regarding the utilization of a combined starter culture composed of three strains of non-Saccharomyces, Saccharomyces cerevisiae and Lactobacillus plantarum for production of wine at the industrial scale. More in-depth, this work investigated the oenological potential of the autochthonous characterized strains from the Apulian region (Southern Italy), Candida zemplinina (syn. Starmerella bacillaris) 35NC1, S. cerevisiae (NP103), and L. plantarum (LP44), in co-inoculation following a complete scale-up scheme. Microbial dynamics, fermentative profiles and production of volatile secondary compounds were assessed in lab-scale micro-vinification tests and then the performances of the mixed starter formulation were further evaluated by pilot-scale wine production. The above results were finally validated by performing an industrial-scale vinification on 100HL of Negroamaro cultivar grape must. The multi-starter formulation was able to rule the different stages of the fermentation processes effectively, and the different microbial combinations enhanced the organoleptic wine features to different extents. The findings indicated that the simultaneous inoculation of the three species affect the quality and quantity of several volatile compounds, confirming that the complexity of the wine can reflect the complexity of the starter cultures. Moreover, the results underlined that the same mixed culture could differently influence wine quality when tested at the lab-, pilot- and industrial-scale. Finally, we highlighted the significance of employment non-Saccharomyces and L. plantarum, together with S. cerevisiae, autochthonous strains in the design of custom-made starter culture formulation for typical regional wine production with pronounced unique quality.

Yeast-Yeast Interactions: Mechanisms, Methodologies and Impact on Composition

During the winemaking process, alcoholic fermentation is carried out by a consortium of yeasts in which interactions occurs. The consequences of these interactions on the wine matrix have been widely described for several years with the aim of controlling the winemaking process as well as possible. In this review, we highlight the wide diversity of methodologies used to study these interactions, and their underlying mechanisms and consequences on the final wine composition and characteristics. The wide variety of matrix parameters, yeast couples, and culture conditions have led to contradictions between the results of the different studies considered. More recent aspects of modifications in the composition of the matrix are addressed through different approaches that have not been synthesized recently. Non-volatile and volatile metabolomics, as well as sensory analysis approaches are developed in this paper. The description of the matrix composition modification does not appear sufficient to explain interaction mechanisms, making it vital to take an integrated approach to draw definite conclusions on them.

Nitrogen Preferences during Alcoholic Fermentation of Different Non-Saccharomyces Yeasts of Oenological Interest

Non-Saccharomyces yeasts have long been considered spoilage microorganisms. Currently, oenological interest in those species is increasing, mostly due to their positive contribution to wine quality. In this work, the fermentative capacity and nitrogen consumption of several non-Saccharomyces wine yeast (Torulaspora delbrueckii, Lachancea thermotolerans, Starmerella bacillaris, Hanseniaspora uvarum, and Metschnikowia pulcherrima) were analyzed. For this purpose, synthetic must with three different nitrogen compositions was used: a mixture of amino acids and ammonium, only organic or inorganic nitrogen. The fermentation kinetics, nitrogen consumption, and yeast growth were measured over time. Our results showed that the good fermentative strains, T. delbrueckii and L. thermotolerans, had high similarities with Saccharomyces cerevisiae in terms of growth, fermentation profile, and nitrogen assimilation preferences, although L. thermotolerans presented an impaired behavior when only amino acids or ammonia were used, being strain-specific. M. pulcherrima was the non-Saccharomyces strain least affected by the nitrogen composition of the medium. The other two poor fermentative strains, H. uvarum and S. bacillaris, behaved similarly regarding amino acid uptake, which occurred earlier than that of the good fermentative species in the absence of ammonia. The results obtained in single non-Saccharomyces fermentations highlighted the importance of controlling nitrogen requirements of the wine yeasts, mainly in sequential fermentations, in order to manage a proper nitrogen supplementation, when needed.

Contribution of non-Saccharomyces yeasts to wine volatile and sensory diversity: A study on Lachancea thermotolerans, Metschnikowia spp. and Starmerella bacillaris strains isolated in Italy

Saccharomyces cerevisiae starter cultures are largely used in winemaking to repress the wild microorganisms and achieve more predictable and desired outcomes. Notwithstanding, alternative microbial resources received increasing attention for their potential to produce wines with more distinctive and typical features. Our previous survey revealed a great inter- and intra-species diversity in an extensive collection of non-Saccharomyces wine yeasts from multiple regions of Italy. This study aimed to explore the detected biodiversity evaluating the quality of wines obtained by sequential inoculation of specific selected strains of the collection (Lachancea thermotolerans or Metschnikowia spp. or Starmerella bacillaris), and S. cerevisiae EC 1118. Fermentations of natural grape must at laboratory scale were followed by microbiological, chemical and sensorial analysis of the wines. The results indicated that each yeast species and strain exerted a distinctive impact on the wine, giving final products clearly separated with Principal Component Analysis. In particular, L. thermotolerans contributed producing relevant amounts of lactic acid and had the highest potential to reduce ethanol content; the presence of S. bacillaris increased the level of glycerol, and, remarkably, reduced acetaldehyde and total SO₂; Metschnikowia spp. promoted the formation of higher alcohols and esters, and reduced volatile phenols. The sensory analysis based on the orthonasal aroma confirmed the separation between the wines obtained with the sequential fermentations and the control with single inoculation of EC 1118, although the three non-Saccharomyces species used could not be clearly distinguishable by the panelists. This study indicates that the use of selected native non-Saccharomyces strains in conjunction with S. cerevisiae positively modulates some relevant chemical parameters, and improves the aromatic intensity of wine, therefore justifying investments in non-conventional yeasts as co-starter cultures.

Characterizing the Potential of the Non-Conventional Yeast Saccharomycodes ludwigii UTAD17 in Winemaking

Non-Saccharomyces yeasts have received increased attention by researchers and winemakers, due to their particular contributions to the characteristics of wine. In this group, Saccharomycodes ludwigii is one of the less studied species. In the present study, a native S. ludwigii strain, UTAD17 isolated from the Douro wine region was characterized for relevant oenological traits. The genome of UTAD17 was recently sequenced. Its potential use in winemaking was further evaluated by conducting grape-juice fermentations, either in single or in mixed-cultures, with Saccharomyces cerevisiae, following two inoculation strategies (simultaneous and sequential). In a pure culture, S. ludwigii UTAD17 was able to ferment all sugars in a reasonable time without impairing the wine quality, producing low levels of acetic acid and ethyl acetate. The overall effects of S. ludwigii UTAD17 in a mixed-culture fermentation were highly dependent on the inoculation strategy which dictated the dominance of each yeast strain. Wines whose fermentation was governed by S. ludwigii UTAD17 presented low levels of secondary aroma compounds and were chemically distinct from those fermented by S. cerevisiae. Based on these results, a future use of this non-Saccharomyces yeast either in monoculture fermentations or as a co-starter culture with S. cerevisiae for the production of wines with greater expression of the grape varietal character and with flavor diversity could be foreseen.

Dynamic changes in norisoprenoids and phenylalanine-derived volatiles in off-vine Vidal blanc grape during late harvest

We investigated the dynamic changes in norisoprenoids and phenylalanine derivatives in off-vine Vidal blanc. Glycosidically bound as well as free-form volatile compounds were identified by GC-MS in two vintages. Thus, off-vine grape exhibited the development of four higher alcohols (viz. linalool oxide, 2-octanol, 1-pentanol, and 1-heptanol), C13-norisoprenoids (α-ionone), phenylalanine-derivates (2-phenylethanol), whereas β-ionone and geranial showed high correlation in on-vine grape. Freeze-thaw cycles and desiccation, two exterior stress affect volatile compound development, resulted in content fluctuations during late harvest. Interestingly, the total content of higher alcohols was higher in on-vine grapes than off-vine grapes in two vintages respectively. Interestingly, the content of higher alcohols was higher in off-vine samples in the 2016 and 2017 vintages. In terms of physicochemical parameters, off-vine Vidal showed results similar to those of on-vine sample. Nevertheless, sensorial impression of the grape juice was influenced by interaction of vintages and vine treatments.

Influence of nitrogen status in wine alcoholic fermentation

Nitrogen is an essential nutrient for yeast during alcoholic fermentation. Nitrogen is involved in the biosynthesis of protein, amino acids, nucleotides, and other metabolites, including volatile compounds. However, recent studies have called several mechanisms that regulate its role in biosynthesis into question. An initial focus on S. cerevisiae has highlighted that the concept of "preferred" versus "non-preferred" nitrogen sources is extremely variable and strain-dependent. Then, the direct involvement of amino acids consumed in the formation of proteins and volatile compounds has recently been reevaluated. Indeed, studies have highlighted the key role of lipids in nitrogen regulation in S. cerevisiae and their involvement in the mechanism of cell death. New winemaking strategies using non-Saccharomyces yeast strains in co- or sequential fermentation improve nitrogen management. Indeed, recent studies show that non-Saccharomyces yeasts have significant and specific needs for nitrogen. Moreover, sluggish fermentation can occur when they are associated with S. cerevisiae, necessitating nitrogen addition. In this context, we will present the consequences of nitrogen addition, discussing the sources, time of addition, transcriptome changes, and effect on volatile compound composition.

Analysis of the NCR Mechanisms in Hanseniaspora vineae and Saccharomyces cerevisiae During Winemaking

There is increasing interest in the use of non-Saccharomyces yeasts in winemaking due to their positive attributes. The non-Saccharomyces yeast Hanseniaspora vineae is an apiculate yeast that has been associated with the production of wine with good fermentation capacity and an increase in aromatic properties. However, this yeast represents a concern in mixed culture fermentation because of its nutrient consumption, especially nitrogen, as its mechanisms of regulation and consumption are still unknown. In this study, we analyzed the nitrogen consumption, as well as the nitrogen catabolism repression (NCR) mechanism, in two genome-sequenced H. vineae strains, using synthetic must fermentations. The use of synthetic must with an established nitrogen content allowed us to study the NCR mechanism in H. vineae, following the amino acid and ammonia consumption, and the expression of genes known to be regulated by the NCR mechanism in S. cerevisiae, AGP1, GAP1, MEP2, and PUT2. H. vineae exhibited a similar amino acid consumption and gene expression profile to S. cerevisiae. However, the wine strain of S. cerevisiae QA23 consumed ammonia and valine more quickly and, in contrast, tyrosine and tryptophan more slowly, than the H. vineae strains. Our results showed a similar behavior of nitrogen regulation in H. vineae and S. cerevisiae, indicating the presence of the NCR mechanism in this Hanseniaspora yeast differentiated before the whole genome duplication event of the Saccharomyces complex. Future study will elucidate if the NCR mechanism is the only strategy used by H. vineae to optimize nitrogen consumption.