Biological aging status characterization of Sherry type wines using statistical and oenological criteria

Influence of flor yeast starters on volatile and nitrogen compounds during a controlled biological aging

Fino Sherry wine undergoes biological aging carried out by a velum of flor yeast within a traditional dynamic system known as "criaderas and solera". The complex microbiota of biofilm-forming Saccharomyces cerevisiae strains play a crucial role in shaping the distinctive organoleptic profile of these types of wines. For this reason, the aim of this study is to analyze the changes produced by different flor yeast strains in the volatilome and the aminogram of different wines from the criaderas and solera system during biological aging in the laboratory, simulating a flor yeast velum condition at different stages of the system. Results suggest that each strain metabolizes wine differently, finding that depending on the wine, some strains are better suited for the process than others. In addition, it is found that the content of biogenic amines in Fino Sherry wines, previously attributed to malolactic bacteria, varies according to the yeast strain metabolizing the wine, suggesting that flor yeast could be used to modify biogenic amines content during biological aging. Results indicate that the use of selected flor yeast starters in biological aging may be of interest to modulate some parameters during Fino Sherry wine aging.

Microbial diversity in sherry wine biofilms and surrounding mites

Sherry wines are film wines produced in the Jerez-Xérès-Sherry and Montilla-Moriles regions in southern Spain which require an aging process under flor biofilms, known as "biological aging". The presence of mites in Sherry wine wineries has been reported and associated with improved wine volatile properties. This work analyzes the microbial diversity in flor biofilms and mites in Sherry wine wineries using Matrix-Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) and ITS/gene amplification. Two mite species, Carpoglyphus lactis and Tyrophagus putrescentiae, were spotted in the sampled winery and 32 microorganism species were identified in their exoskeleton or surrounding biofilms. To our knowledge, 26 of these species were never described before in sherry wine environments. We hypothesized that mites feed on the flor biofilms as well as another type of biofilm located in barrel cracks, known by winemakers as "natas" (cream in English). These non-studied biofilms showed the highest microbiome diversity among all samples (followed by C. lactis spotted nearby) thus, representing a niche of microorganisms with potential biotechnological interest. Besides mites, Drosophila flies were spotted in the sampling areas. The role of flies and mites as vectors that transport microorganisms among different niches (i.e., flor biofilms and natas) is discussed.

Flor yeast immobilization in microbial biocapsules for Sherry wine production: microvinification approach

Sherry wine is a pale-yellowish dry wine produced in Southern-Spain which features are mainly due to biological aging when the metabolism of biofilm-forming yeasts (flor yeasts) consumes ethanol (and other non-fermentable carbon sources) from a previous alcoholic fermentation, and produces volatile compounds such as acetaldehyde. To start aging and maintain the wine stability, a high alcohol content is required, which is achieved by the previous fermentation or by adding ethanol (fortification). Here, an alternative method is proposed which aims to produce a more economic, distinctive Sherry wine without fortification. For this, a flor yeast has been pre-acclimatized to glycerol consumption against ethanol, and later confined in a fungal-based immobilization system known as "microbial biocapsules", to facilitate its inoculum. Once aged, the wines produced using biocapsules and free yeasts (the conventional method) exhibited chemical differences in terms of acidity and volatile concentrations. These differences were evaluated positively by a sensory panel. Pre-acclimatization of flor yeasts to glycerol consumption was not successful but when cells were immobilized in fungal pellets, ethanol consumption was lower. We believe that immobilization of flor yeasts in microbial biocapsules is an economic technique that can be used to produce high quality differentiated Sherry wines.

Influencia de la reducción del grado alcohólico en los vinos de crianza biológica sobre sus características físico-químicas y sensoriales. Primeros resultados

Las Denominaciones de Origen Protegidas Jerez-Xérez-Sherry, Manzanilla Sanlúcar de Barrameda y Montilla-Moriles son de las más antiguas de España. En ellas se elaboran los vinos tipo Fino y Manzanilla mediante una etapa de crianza biológica bajo velo de Flor durante varios años. Estos vinos, que presentan características organolépticas específicas, tienen establecido una graduación alcohólica mínima del 15% (14,5% en el caso de los vinos Finos sin alcohol añadido en la DO Montilla-Moriles).

Los gustos de los consumidores van cambiando y cada vez hay una mayor preocupación por la salud, por lo que la tendencia actual es la de consumir bebidas alcohólicas con un contenido en alcohol moderado. En el presente trabajo, se ha estudiado la viabilidad de elaborar vinos tipo Fino y Manzanilla con un grado alcohólico más reducido. Los primeros resultados nos indican que es viable elaborar esta tipología de vinos con un menor contenido en alcohol, manteniendo la elaboración tradicional y calidad de estos vinos, aunque es un proceso que habrá que seguir estudiando a largo plazo.

Valorization of Traditional Alcoholic Beverages: The Study of the Sicilian Amarena Wine during Bottle Aging

Traditional alcoholic beverages have always been part of the Mediterranean culture and, lately, they have been re-evaluated to valorize both the territory and local customs. In this study, the Amarena wine, a fortified wine included in the national list of the traditional agri-food products, was characterized during bottle aging for oenological parameters, chromaticity, volatiles, and inorganic elements. Then, experimental data were visually interpreted by a principal component analysis (PCA). PCA revealed that most of oenological parameters (i.e., alcoholic grade, total dry extract, sugars, organic acids, and phenolic compounds) had a scarce discriminating power. Additionally, ethyl esters were only present in younger products, while remaining at quite constant levels. Conversely, certain metals (i.e., Mg, Na, Mn, Zn, and Cu), chromatic properties, and pH differentiated older Amarena bottles from the younger counterpart. Particularly, acetaldehyde and furanic compounds proved to be valid aging markers. A sensorial analysis highlighted that fruity and floral odors and flavors characterized younger beverages, while dried fruity, nutty, and spicy notes were displayed by older products, along with the valuable attribute of “oxidized” typically observed in aged Sherry wines. Overall, this study may encourage the production and commercialization of the Amarena wine, thus preserving the cultural heritage of the Mediterranean area.

Revealing the Yeast Diversity of the Flor Biofilm Microbiota in Sherry Wines Through Internal Transcribed Spacer-Metabarcoding and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry

Flor yeast velum is a biofilm formed by certain yeast strains that distinguishes biologically aged wines such as Sherry wine from southern Spain from others. Although Saccharomyces cerevisiae is the most common species, 5.8 S-internal transcribed spacer (ITS) restriction fragment length polymorphism analyses have revealed the existence of non-Saccharomyces species. In order to uncover the flor microbiota diversity at a species level, we used ITS (internal transcribed spacer 1)-metabarcoding and matrix-assisted laser desorption/Ionization time of flight mass spectrometry techniques. Further, to enhance identification effectiveness, we performed an additional incubation stage in 1:1 wine:yeast extract peptone dextrose (YPD) before identification. Six species were identified: S. cerevisiae, Pichia manshurica, Pichia membranifaciens, Wickerhamomyces anomalus, Candida guillermondii, and Trichosporon asahii, two of which were discovered for the first time (C. guillermondii and Trichosporon ashaii) in Sherry wines. We analyzed wines where non-Saccharomyces yeasts were present or absent to see any potential link between the microbiota and the chemical profile. Only 2 significant volatile chemicals (out of 13 quantified), ethanol and ethyl lactate, and 2 enological parameters (out of 6 quantified), such as pH and titratable acidity, were found to differ in long-aged wines. Although results show a low impact where the non-Saccharomyces yeasts are present, these yeasts isolated from harsh environments (high ethanol and low nutrient availability) could have a potential industrial interest in fields such as food microbiology and biofuel production.

Analyzing the minor volatilome of Torulaspora delbrueckii in an alcoholic fermentation

Torulaspora delbrueckii is an emerging yeast species in the beverage and food industry that is suitable for alcoholic fermentation and to improve the organoleptic quality of wine, beer, mead, and other beverages. Modern consumer preference toward new flavors and products drives the application of T. delbrueckii to ferment less traditional fruits and vegetables. Thus, it has become increasingly relevant to define those metabolites produced in minute quantities by T. delbrueckii, because they may have an impact when producing these new alcoholic beverages. In this study, we have identified metabolites of T. delbrueckii and have compared them with those of Saccharomyces cerevisiae in a controlled setting with a synthetic, high glucose medium using gas chromatography coupled to flame ionization detector (GC–FID) and stir bar sorptive extraction (SBSE) with GC coupled to mass spectrometry (MS). Results showed that T. delbrueckii produced metabolites with higher changes in odor activity complexes than S. cerevisiae: ethyl propanoate, 1,1-diethoxyethane, ethyl isobutyrate, ethyl butyrate, isoamyl acetate, ethyl heptanoate, nonanal, and decanal. We also report seven metabolites detected for the first time in T. delbrueckii. This datum serves to expand the knowledge of T. delbrueckii performance and shows that application of this yeast species is more suitable to a wide array of beverage producers.

Cultivable microbial ecology and aromatic profile of "mothers" for Vino cotto wine production

The aim of the present study was to assess the cultivable microbiota of "mothers" of Vino cotto collected from production of different years 1890, 1895, 1920, 1975, 2008. A total of 73 yeasts and 81 bacteria were isolated. Starmerella lactis-condensi, Starmerella bacillaris, Hanseniaspora uvarum, Saccharomyces cerevisiae, Hanseniaspora guillermondi and Metschnikowia pulcherrima were identified. Bacteria isolates belonged to lactic acid bacteria (Lactiplantibacillus plantarum and Pediococcus pentosaceus) and acetic acid bacteria (Gluconobacter oxydans). Remarkable biodiversity was observed for Starm. bacillaris, as well as L. plantarum and G. oxydans. Organic acids and volatile compounds were also determined. Malic and succinic acids were the main ones with values ranging from 8.49 g/L to 11.76 g/L and from 4.15 g/L to 7.73 g/L respectively, while citric acid was present at low concentrations (<0.2 g/L) in all samples. Esters and higher alcohols were the main volatile compounds detected followed by alkanes. This study permits to better understand the microbial communities associated to this product and could be considered a starting point for the definition of tailored starter cultures to improve the quality of Vino cotto preserving its typical traits.

Comparative analysis of intracellular metabolites, proteins and their molecular functions in a flor yeast strain under two enological conditions

Flor yeasts confer a wide range of organoleptic properties to Sherry-type wines during a process called "biological aging" that takes place after alcoholic fermentation. These kinds of yeasts adapt to a biological aging condition by forming a biofilm known as "flor velum" and by changing from fermentative to oxidative metabolism. It has been reported that some functions such as increase of cell surface hydrophobicity or changes to lipid metabolism are enhanced when yeasts switch to biofilm lifestyle. Here, we attempt to reveal intracellular metabolites and protein molecular functions not documented before that are relevant in biofilm formation and in fermentation by an endometabolome and proteome screening. We report that at early stages of biofilm formation, flor yeasts accumulate mannose, trehalose, glycerol, oleic and stearic acids and synthesize high amounts of GTPases, glycosylases and lipoproteins. On the other hand, in early fermentation, flor yeasts rapidly consume glucose and phosphoric acid; and produce abundant proteins related to chromatin binding, transcription factors and methyl transferases.

Biogenic amines and other polar compounds in long aged oxidized Vernaccia di Oristano white wines

Oxidized white wines are produced by techniques that provide a barrel ageing which can range from a few years to some decades. This step, characterized by the metabolic activity of peculiar strains of Saccharomyces cerevisiae yeast, can affect the chemical composition of these wines and the production of unwanted substances such as biogenic amines. In this study, Vernaccia di Oristano wines from different vintages have been analysed for the first time regarding the content of biogenic amines and amino acids (by HPLC-FLD), and polar compounds (by HPLC-DAD and LC-MS). Furthermore, colour and technological parameters (contents of alcohol, reducing sugars, total and volatile acidities, pH and organic acids) of the wines were also evaluated. Older samples showed dark shades, which may have derived from polyphenols' oxidation while ageing. Some typical ageing products, such as 5-(hydroxymethyl)furfural and hydroxycinnamic acid derivatives were found in larger quantities in these samples, as well as the purinic compound xanthine, which was also detected in relevant concentrations. Additionally, as expected, the average of the main biogenic amines quantified in Vernaccia di Oristano was higher compared to non-oxidized white wines, especially in the older samples. Thus, though this content does not exceed values which spoil the quality of the wine, the monitoring of the winemaking conditions is suggested, to further limit the presence of these undesirable compounds.

Yeast Immobilization Systems for Alcoholic Wine Fermentations: Actual Trends and Future Perspectives

Yeast immobilization is defined as the physical confinement of intact cells to a region of space with conservation of biological activity. The use of these methodologies for alcoholic fermentation (AF) offers many advantages over the use of the conventional free yeast cell method and different immobilization systems have been proposed so far for different applications, like winemaking. The most studied methods for yeast immobilization include the use of natural supports (e.g., fruit pieces), organic supports (e.g., alginate), inorganic (e.g., porous ceramics), membrane systems, and multi-functional agents. Some advantages of the yeast-immobilization systems include: high cell densities, product yield improvement, lowered risk of microbial contamination, better control and reproducibility of the processes, as well as reuse of the immobilization system for batch fermentations and continuous fermentation technologies. However, these methods have some consequences on the behavior of the yeasts, affecting the final products of the fermentative metabolism. This review compiles current information about cell immobilizer requirements for winemaking purposes, the immobilization methods applied to the production of fermented beverages to date, and yeast physiological consequences of immobilization strategies. Finally, a recent inter-species immobilization methodology has been revised, where yeast cells are attached to the hyphae of a Generally Recognized As Safe fungus and remain adhered following loss of viability of the fungus. The bio-capsules formed with this method open new and promising strategies for alcoholic beverage production (wine and low ethanol content beverages).

Population analysis of biofilm yeasts during fino sherry wine aging in the Montilla-Moriles D.O. region

Fino is the most popular sherry wine produced in southern Spain. Fino is matured by biological aging under a yeast biofilm constituted of Saccharomyces cerevisiae yeasts. Although different S. cerevisiae strains can be identified in such biofilms, their diversity and contribution to wine character have been poorly studied. In this work, we analyse the flor yeast population in five different wineries from the Montilla-Moriles D.O. (Denominación de Origen) in southern Spain. Yeasts present in wines of different ages were identified using two different culture-dependent molecular techniques. From 2000 individual yeast isolates, five different strains were identified with one of them dominating in four out of the five wineries analysed, and representing 76% of all the yeast isolates collected. Surprisingly, this strain is similar to the predominant strain isolated twenty years ago in Jerez D.O. wines, suggesting that this yeast is particularly able to adapt to such a stressful environment. Fino wine produced with pure cultures of three of the isolated strains resulted in different levels of acetaldehyde. Because acetaldehyde levels are a distinctive characteristic of fino wines and an indicator of fino aging, the use of molecular techniques for yeast identification and management of yeast populations may be of interest for fino wine producers looking to control one of the main features of this wine.

Use of a flor velum yeast for modulating colour, ethanol and major aroma compound contents in red wine

The most important and negative effect of the global warming for winemakers in warm and sunny regions is the observed lag between industrial and phenolic grape ripeness, so only it is possible to obtain an acceptable colour when the ethanol content of wine is high. By contrast, the actual market trends are to low ethanol content wines. Flor yeast growing a short time under velum conditions, decreases the ethanol and volatile acidity contents, has a favorable effect on the colour and astringency and significantly changes the wine content in 1-propanol, isobutanol, acetaldehyde, 1,1-diethoxiethane and ethyl lactate. The Principal Component Analysis of six enological parameters or five aroma compounds allows to classify the wines subjected to different velum formation conditions. The obtained results in two tasting sessions suggest that the flor yeast helps to modulate the ethanol, astringency and colour and supports a new biotechnological perspective for red winemakers.

Flor Yeast: New Perspectives Beyond Wine Aging

The most important dogma in white-wine production is the preservation of the wine aroma and the limitation of the oxidative action of oxygen. In contrast, the aging of Sherry and Sherry-like wines is an aerobic process that depends on the oxidative activity of flor strains of Saccharomyces cerevisiae. Under depletion of nitrogen and fermentable carbon sources, these yeast produce aggregates of floating cells and form an air–liquid biofilm on the wine surface, which is also known as velum or flor. This behavior is due to genetic and metabolic peculiarities that differentiate flor yeast from other wine yeast. This review will focus first on the most updated data obtained through the analysis of flor yeast with -omic tools. Comparative genomics, proteomics, and metabolomics of flor and wine yeast strains are shedding new light on several features of these special yeast, and in particular, they have revealed the extent of proteome remodeling imposed by the biofilm life-style. Finally, new insights in terms of promotion and inhibition of biofilm formation through small molecules, amino acids, and di/tri-peptides, and novel possibilities for the exploitation of biofilm immobilization within a fungal hyphae framework, will be discussed.

Proteins involved in wine aroma compounds metabolism by a Saccharomyces cerevisiae flor-velum yeast strain grown in two conditions

A proteomic and exometabolomic study was conducted on Saccharomyces cerevisiae flor yeast strain growing under biofilm formation condition (BFC) with ethanol and glycerol as carbon sources and results were compared with those obtained under no biofilm formation condition (NBFC) containing glucose as carbon source. By using modern techniques, OFFGEL fractionator and LTQ-Orbitrap for proteome and SBSE-TD-GC-MS for metabolite analysis, we quantified 84 proteins including 33 directly involved in the metabolism of glycerol, ethanol and 17 aroma compounds. Contents in acetaldehyde, acetic acid, decanoic acid, 1,1-diethoxyethane, benzaldehyde and 2-phenethyl acetate, changed above their odor thresholds under BFC, and those of decanoic acid, ethyl octanoate, ethyl decanoate and isoamyl acetate under NBFC. Of the twenty proteins involved in the metabolism of ethanol, acetaldehyde, acetoin, 2,3-butanediol, 1,1-diethoxyethane, benzaldehyde, organic acids and ethyl esters, only Adh2p, Ald4p, Cys4p, Fas3p, Met2p and Plb1p were detected under BFC and as many Acs2p, Ald3p, Cem1p, Ilv2p, Ilv6p and Pox1p, only under NBFC. Of the eight proteins involved in glycerol metabolism, Gut2p was detected only under BFC while Pgs1p and Rhr2p were under NBFC. Finally, of the five proteins involved in the metabolism of higher alcohols, Thi3p was present under BFC, and Aro8p and Bat2p were under NBFC.