Evaluation of the active odorants in Amontillado sherry wines during the aging process

Insights into microbial communities and metabolic profiles in the traditional production of the two representative Hongqu rice wines fermented with Gutian Qu and Wuyi Qu based on single-molecule real-time sequencing

Hongqu rice wine, a famous traditional fermented alcoholic beverage, is brewed with traditional Hongqu (mainly including Gutian Qu and Wuyi Qu). This study aimed to compare the microbial communities and metabolic profiles in the traditional brewing of Hongqu rice wines fermented with Gutian Qu and Wuyi Qu. Compared with Hongqu rice wine fermented with Wuyi Qu (WY), Hongqu rice wine fermented with Gutian Qu (GT) exhibited higher levels of biogenic amines. The composition of volatile flavor components of Hongqu rice wine brewed by different fermentation starters (Gutian Qu and Wuyi Qu) was obviously different. Among them, ethyl acetate, isobutanol, 3-methylbutan-1-ol, ethyl decanoate, ethyl palmitate, ethyl oleate, nonanoic acid, 4-ethylguaiacol, 5-pentyldihydro-2(3H)-furanone, ethyl acetate, n-decanoic acid etc. were identified as the characteristic aroma-active compounds between GT and WY. Microbiome analysis based on high-throughput sequencing of full-length 16S rDNA/ITS-5.8S rDNA amplicons revealed that Lactococcus, Leuconostoc, Pseudomonas, Serratia, Enterobacter, Weissella, Saccharomyces, Monascus and Candida were the predominant microbial genera during the traditional production of GT, while Lactococcus, Lactobacillus, Leuconostoc, Enterobacter, Kozakia, Weissella, Klebsiella, Cronobacter, Saccharomyces, Millerozyma, Monascus, Talaromyces and Meyerozyma were the predominant microbial genera in the traditional fermentation of WY. Correlation analysis revealed that Lactobacillus showed significant positive correlations with most of the characteristic volatile flavor components and biogenic amines. Furthermore, bioinformatical analysis based on PICRUSt revealed that microbial enzymes related to biogenic amines synthesis were more abundant in GT than those in WY, and the enzymes responsible for the degradation of biogenic amines were less abundant in GT than those in WY. Collectively, this study provides important scientific data for enhancing the flavor quality of Hongqu rice wine, and lays a solid foundation for the healthy and sustainable development of Hongqu rice wine industry.

Determination of volatile compounds for the differentiation of PDO fortified wines with different ageing methods as a tool for controlling their authenticity

The aim of this work was to study the differentiating volatile profiles of the Spanish protected designation of origin (PDO) fortified wines obtained by headspace solid phase microextraction in conjunction with gas chromatography-mass spectrometry and powerful chemometric tools, to finally identify the marker volatile compounds most related to fortified wine types. Results revealed a satisfactory discrimination, for the first time, of the different types of PDO fortified wines, involving only a reduced number of volatile compounds selected by chemometrics. Thus, 28 volatile compounds were responsible for the differentiation according to ageing type (biological, oxidative, or mixed) resulting useful markers for the identification of each specific type of fortified wine. Among them, some esters were strongly related to biological ageing, aldehydes and acids to oxidative ageing, and lactones to mixed ageing. These volatile molecules involved in their differentiation could explain the unique organoleptic characteristics or attributes of these PDO fortified wines.

Identification of the key odor-active compounds responsible for varietal smoky aroma in wines made from the East Asian species

A smoky aroma was found in wines made from East Asian species that had not been treated with oak products or exposed to smoke. In this study, a combined method of sensory analysis and quantitation of aroma compounds was used to identify the chemical basis of this smoky aroma. Syringol, eugenol, 4-ethylguaiacol, and 4-ethylphenol were confirmed as the key odor-active compounds contributing to the varietal smoky notes in wines of East Asian species. The concentrations of these compounds showed significant variation between grape species. The highest levels of syringol were found in Vitis amurensis wines, with an average of 178.8 μg/L. The average concentration of eugenol in V. davidii wines was 101.5 μg/L, about 10 times higher than in other species. 4-Ethylphenol and 4-ethylguaiacol were both abundant in the wines of the East Asian species. The results of the sensory interaction between the four compounds showed a complete addition effect for eugenol, a partial addition effect for syringol, and a hyper-addition effect for 4-ethylguaiacol and 4-ethylphenol on the smoky attribute.

The Fingerprint of Fortified Wines-From the Sui Generis Production Processes to the Distinctive Aroma

The fortified wines that originated in Mediterranean countries have, in common, a high alcohol content to increase their shelf-life during long journeys to northern Europe and the American continent. Nowadays, the world's better-known wines, including Marsala, Madeira, Port, and Sherry, due to their high alcoholic content, sweet taste, and intense aromatic profile, are designated as dessert wines and sometimes served as aperitifs. This review gives an overview of the traditional vinification process, including the microbiota and autochthonous yeast, as well as the regulatory aspects of the main Italian, Portuguese, and Spanish fortified wines. The winemaking process is essential to defining the volatile organic compounds (VOCs) that characterize the aroma of each fortified wine, giving them an organoleptic fingerprint and "terroir" characteristics. The various volatile and odorous compounds found in fortified wines during the oxidative aging are discussed in the last part of this review.

Analytical, Chemometric and Sensorial Characterization of Oloroso and Palo Cortado Sherries during Their Ageing in the Criaderas y Solera System

Oloroso and Palo Cortado are two types of sherry wines, produced in the Sherry Wine Region in Southern Spain, known as Marco de Jerez, where it is aged following the traditional Criaderas y Solera system. All of them are aged through oxidative ageing, even though the peculiar Palo Cortado Sherry wine is also aged biologically under a veil of flor yeasts in the first stage. Total dry extract, organic acids, aldehydes, esters, higher alcohols and phenolic compounds in these sherry wines evolve during their ageing as a consequence of evaporation and/or perspiration processes, chemical reactions, extraction of compounds from oakwood and microbiological activity. Sherry wines develop their characteristic organoleptic profile during their ageing, as could be proven through their tasting sessions. According to the sherry type, some natural groupings of the wines could be observed after their principal component analysis. Furthermore, by multiple linear regression methods, an important correlation between the parameters that were analyzed and the ageing of each specific wine has been confirmed, which allowed us to establish two different models, each corresponding to the sherry type in question. Only five of the variables that were investigated were required to successfully estimate each wine's age at over 99% confidence. This represents a rather convenient tool for wineries to monitor the ageing of these sherry wines.

Sherry Wines: Worldwide Production, Chemical Composition and Screening Conception for Flor Yeasts

The manufacturing of sherry wines is a unique, carefully regulated process, from harvesting to quality control of the finished product, involving dynamic biological aging in a “criadera-solera” system or some other techniques. Specialized “flor” strains of the yeast Saccharomyces cerevisiae play the central role in the sherry manufacturing process. As a result, sherry wines have a characteristic and unique chemical composition that determines their organoleptic properties (such as color, odor, and taste) and distinguishes them from all other types of wine. The use of modern methods of genetics and biotechnology contributes to a deep understanding of the microbiology of sherry production and allows us to define a new methodology for breeding valuable flor strains. This review discusses the main sherry-producing regions and the chemical composition of sherry wines, as well as genetic, oenological, and other selective markers for flor strains that can be used for screening novel candidates that are promising for sherry production among environmental isolates.

A Comparative Study of Yeasts for Rosa roxburghii Wine Fermentation

Wine produced by fermentation of Chestnut rose (Rosa roxburghii) hips, known as cili (Chinese-Mandarin), in Guizhou province, and other places in China is becoming popular but there is limited knowledge of suitable yeast strains for its production. In this study, we first investigated the oenological properties of six commercial S. cerevisiae yeast strains (X16, F33, SH12, GV107, S102, RMS2), one commercial Saccharomyces cerevisiae var. bayanus (S103), one commercial, non-Saccharomyces yeast strain, Torulaspora delbrueckii Prelude, and one indigenous S. cerevisiae strain, CZ, for cili wine fermentation. We measured the key traits of each of the yeast strains, viz., sulfite resistance, flocculation, hydrogen sulfide production capacity, fermentation rate, and yeast growth curves. Subsequently, we measured the resultant wine characteristics, viz., pH, alcohol content, residual sugar, titratable acidity, volatile acidity, ascorbic acid content and headspace volatile compounds. The overall suitability of each yeast type was evaluated using a multi-factor, unweighted, scorecard. On that basis, RMS2 was the most suitable, and closely followed by CZ and X16. This study is the first comparative evaluation of yeasts for cili wine production and provides a preliminary guide for their selection.

Analytical and Chemometric Characterization of Fino and Amontillado Sherries during Aging in Criaderas y Solera System

Fino and Amontillado are Sherry wines, produced in Marco de Jerez area (southern Spain), and aged in Criaderas y Solera system. Fino Sherry wine follows a biological aging process, under a veil of flor yeasts, while Amontillado Sherry wine shares the same biological aging firstly, followed by oxidative aging, which gives them special features. Organic acids, esters, higher alcohols, phenolic compounds and total dry extract of Sherries evolve during aging due to evaporation processes, physical-chemical reactions, wood contributions and microbiological activity. During aging, Sherry wines improve their organoleptic profile, as could be proved in the tasting sessions. Hierarchical Cluster Analysis and Factor Analysis with factor extraction using Principal Components of Sherry wines studied were carried out and natural groupings of the wines according to the type of aging and their age were observed. A strong correlation between the parameters analyzed and the aging of each wine has been seen in the Multiple Linear Regression studies, establishing two different models, one for each type of Sherry wine, that, with only four of all the variables studied estimated the wine age with more than 99% of confidence. This constitutes a useful tool to control the age of these Sherry wines in the winery.

Characteristic fingerprints and volatile flavor compound variations in Liuyang Douchi during fermentation via HS-GC-IMS and HS-SPME-GC-MS

The present study investigates volatile organic compound (VOC) compositional changes in Liuyang Douchi during fermentation via a HS-GC-IMS and HS-SPME-GC-MS combination approach. A total of 115 VOCs were identified from Douchi, most of which were accumulated during pile fermentation. Notably, most alcohols and acids decreased with fermentation, while esters, ketones, pyrazines, and phenols accumulated during pile fermentation. Depending on the VOCs identified by GC-IMS/MS, the different fermentation stages of Douchi could be facilely distinguished. Of these, 49 VOCs were regarded as the marker VOCs of Douchi in different fermentation stage: hexanol, hexanal, and propanoic acid was the marker VOCs of the black beans before fermentation and contributing beany and grassy odors; 1-octen-3-ol and 3-octanone supplying a mushroom aroma to the Douchi fermented for 3-9 days; and esters and pyrazine, especially ethyl acetate and 2,6-dimethylpyrazine, contributing the cocoa, fruity, and nutty aromas of matured Douchi.

Stress Resistance and Adhesive Properties of Commercial Flor and Wine Strains, and Environmental Isolates of Saccharomyces cerevisiae

Flor strains of Saccharomyces cerevisiae represent a special group of yeasts used for producing biologically aged wines. We analyzed the collection of commercial wine and flor yeast strains, as well as environmental strains isolated from the surface of grapes growing in vineyards, for resistance to abiotic stresses, adhesive properties, and the ability to form a floating flor. The degree of resistance of commercial strains to ethanol, acetaldehyde, and hydrogen peroxide was generally not higher than that of environmental isolates, some of which had high resistance to the tested stress agents. The relatively low degree of stress resistance of flor strains can be explained both by the peculiarities of their adaptive mechanisms and by differences in the nature of their exposure to various types of stress in the course of biological wine aging and under the experimental conditions we used. The hydrophobicity and adhesive properties of cells were determined by the efficiency of adsorption to polystyrene and the distribution of cells between the aqueous and organic phases. Flor strains were distinguished by a higher degree of hydrophobicity of the cell surface and an increased ability to adhere to polystyrene. A clear correlation between biofilm formation and adhesive properties was also observed for environmental yeast isolates. The overall results of this study indicate that relatively simple tests for cell hydrophobicity can be used for the rapid screening of new candidate flor strains in yeast culture collections and among environmental isolates.

Aroma of Sherry Products: A Review

Jerez (Sherry) is a well-known wine-producing region located in southern Spain, where world-renowned oenological products such as wines, vinegars, and brandies are produced. There are several factors that provide characteristic physical, chemical, and sensory properties to the oenological products obtained in this Sherry region: the climate in the area with hot summers, mild winters, and with limited rainfall; the raw material used consisting on Palomino Fino, Moscatel, and Pedro Ximénez white grape varieties; the special vinification with fortified wines; and aging techniques such as a dynamic system of biological or oxidative aging. These special organoleptic characteristics are responsible for, among others, the aromatic profile of the wines, vinegars and brandies from the area, which explains why this is a subject that has been extensively researched over the years. This bibliographic review aims to compile the different scientific contributions that have been found to date, in relation with the aroma of the oenological products from the Sherry area (dry wines, sweet wines, vinegars, and brandies). We have mainly focused on the different analytical methodologies used and on the main analytes of interest.

Comparative Evaluation of Key Aroma-Active Compounds in Sweet Osmanthus (Osmanthus fragrans Lour.) with Different Enzymatic Treatments

Sweet osmanthus (Osmanthus fragrans Lour.) (OF) is one of the ten most famous flowers in China for its unique and delicate fragrance. A combined solid-phase microextraction and solvent-assisted flavor evaporation method was used to accurately capture the overall aromatic profile and characterize the predominant odorants of fresh osmanthus with the help of gas chromatography (GC)-olfactometry and comprehensive two-dimensional GC-quadrupole time-of-flight mass spectrometry (GC × GC-QTOF-MS). Twenty-six volatiles were identified for the first time in OF. A total of 23 potent odorants, dominated by monoterpene oxides and C₆ aliphatic aldehydes, were identified. The efficacy of pectinase, β-glucosidase, and their combination on the aroma enhancement of OF was evaluated by quantitation of the target aroma components using GC-triple quadrupole-MS. The total concentration of key aroma components increased in all three enzyme treatment groups, and the increase was more significant in two β-glucosidase-treated groups. Changes in odor activity values and odor spectrum values of key odorants indicated that the pectinase-treated sample had more prominent floral, green, and potato-like scents. In contrast, the β-glucosidase-treated sample had more dominant floral, woody, almond-like, and fruity notes but less green odor, which was confirmed by sensory evaluation. β-Glucosidase and pectinase complement one another very well, and together, promote a remarkable aroma enhancement in OF.

Comprehensive investigation of lactones and furanones in icewines and dry wines using gas chromatography-triple quadrupole mass spectrometry

A number of lactones and furanones associated with pleasant odorants play a vital role in grape and wine aroma profiles. However, they are usually present at trace levels and are particularly challenging to measure. In this work, an optimized method based on solid-phase extraction (SPE) coupled with gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS/MS) was developed for simultaneous determination of 14 lactones and 3 furanones. The validation was carried out using different types of wine as matrices, and satisfactory linearity, sensitivity, trueness and precision were confirmed. Furaneol and sotolon showed significantly lower limits of detection (LODs) in three real wines compared to model wine due to the matrix effect. Furthermore, the method was successfully applied to investigate the concentration range of lactones and furanones in several icewines, dry red and white wines. Icewines contained higher concentrations of most lactones and furanones compared with dry red and white wines. Partial least squares-discriminate analysis (PLS-DA) also indicated that γ-hexa-, γ-octa-, γ-nona-, γ-deca-, δ-hexa-, and δ-decalactone, as well as 5,6-dihydro-6-pentyl-2H-pyran-2-one (C10 massoia lactone), sotolon and homofuraneol contributed greatly to the discrimination between icewines and dry wines. Moreover, the calculation of odor activity value (OAV) suggested that γ-octa-, γ-nona-, and γ-decalactone, as well as furaneol and homofuraneol contributed greatest to the aroma of icewines.

Identification of key odorants in complex mixtures occurring in nature

Covering: up to 2019Soon after the birth of gas chromatography, mass spectrometry and olfactometry were used as detectors, which allowed impressive development to be achieved in the area of odorant determinations. Since the mid-80s, structured methods of gas chromatography-olfactometry have appeared, allowing the determination of which odor constituents play a key role in materials. Progressively, numerous strategies have been proposed for sample preparation from raw materials, the representativeness evaluation of extracts, the identification of odor constituents, their quantification, and subsequently, the recombination of the key odorants to mimic the initial odor. However, the multiplicity of options at each stage of the analysis leads to a confusing landscape in this field, and thus, the present review aims at critically presenting the available options. For each step, the most frequently used alternatives are described, together with their strengths and weaknesses based on theoretical and experimental justifications according to the literature. These techniques are exemplified by many applications in the literature on aromas, fragrances and essential oils, with the initial focus on wine odorants, followed by a short overview on the molecular diversity of key odorants, which illustrates most of the facets and complexities of odor studies, including the issues raised by odorant interactions such as synergies.

Physicochemical and microbiological characterization of the sensory deviation responsible for the origin of the special sherry wines "palo cortado" type

The aim of this study was to characterize the biochemical changes and microbiological processes involved in the sensory deviation of "sobretablas" wines during biological aging, which leads to the origin of special or rare "palo cortado" wines. Industrial trials of biological aging of "sobretablas" wines with the potential for the development of lactic acid bacteria (LAB) were performed to study this phenomenon. The results showed that sensory deviation was due to the development of malolactic fermentation (MLF) together with an attenuated aerobic metabolism of "flor" yeast. Malolactic fermentation (MLF) was promoted by the presence of malic acid concentrations that were higher than 1 g/L and the coexistence of LAB and "flor" velum yeast. Ethyl lactate, acetoin and 2,3-butanediol are some of the volatile compounds that are responsible for this sensory deviation. Wines with high levels of gluconic and malic acids (> 1 g/L) can cause, with very low probability, the sensory deviation of "palo cortado". A lysozyme dose of 12 g/hL is an effective treatment to avoid malolactic fermentation (MFL) and sensory deviation. Understanding the biochemical and microbiological changes involved in sensory deviation can be useful to wineries as markers to identify the origin of the special sherry wines "palo cortado" type.

Characterization of the key aroma compounds in a commercial Amontillado sherry wine by means of the sensomics approach

An aroma extract dilution analysis (AEDA) carried out on the volatile fraction isolated by extraction/solvent-assisted flavor evaporation (SAFE) distillation from a commercial Amontillado sherry wine revealed 37 odor-active compounds with flavor dilution (FD) factors in the range of 16-4096. Among them, 2-phenylethanol (flowery, honey-like) and ethyl methylpropanoate (fruity) showed the highest FD factors, followed by ethyl (2S,3S)-2-hydroxy-3-methylpentanoate (fruity) reported for the first time in sherry wine. A total of 36 aroma-active compounds located by AEDA were then quantitated by a stable isotope dilution assay, and their odor activity values (OAVs; ratio of concentration to odor threshold) were calculated. The highest OAV was displayed by 1,1-diethoxyethane (2475; fruity), followed by 2- and 3-methylbutanals (574; malty) and methylpropanal (369; malty). Aroma reconstitution experiments and a comparative aroma profile analysis revealed that the entire orthonasal aroma profile of the Amontillado sherry wine could be closely mimicked.

Model aging and oxidation effects on varietal, fermentative, and sulfur compounds in a dry botrytized red wine

From harvest until wine arrives to the consumer, oxygen plays a crucial role in the definition of the final aroma. In the present research, the effect of the model oxidative aging on a dry red Botrytis wine, such as Italian Amarone, was considered. Amarone wine was submitted to model oxidative aging and then analyzed with two different approaches (SPE-GC-MS and HS-SPME/GC-MS). The same sampling plan was adopted to study the model aging of the same Amarone wine in anaerobic conditions. The HS-SPME/GC-MS method was applied to investigate for the first time the effect of the oxidative aging on a vast number of fermentative sulfur compounds. This research highlighted peculiar evolutions for several volatile compounds. In particular, benzaldehyde showed a sensitive increment during the oxidative aging, with a rate much higher than that reported for non-Botrytis red wines. On the other hand, several sulfides (dimethyl sulfide, 3-(methylthio)-1-propanol, etc.) disappeared after just 15 days of oxidative aging. A wine oxidation marker such as 3-(methylthio)-propanal was not found in any of the oxidized wines; conversely methionol-S-oxide was tentatively identified. This evidence has not been mentioned in the literature. A possible involvement of grape withering process and Botrytis in these mechanisms was supposed: a dry red wine, produced from the same but without any grape withering process and Botrytis infection (e.g., Bardolino wine), was submitted to oxidative aging and analysis. This red wine showed an evolution similar to those reported in the literature for dry red wines but significantly different from the Amarone wine.

Sherry wines

Sherry wines are among the most distinctive Spanish wines, mainly produced in the southern Spain (particularly in Jerez and Montilla-Moriles), using traditional practices aimed at ensuring uniform quality and characteristics over time. Several types of Sherry wines are produced depending on the winemaking conditions. Fino-type wines are characterized by a dynamic biological aging, in which a layer of yeast grows in the surface of the wine (flor velum). On the contrary, Oloroso-type sherry wines are subjected to an oxidative aging, while Amontillado-type Sherries are produced by combining both production systems. Therefore, these wines undergo different biological and chemical processes that affect distinctively their chemical composition and their aroma and sensory characteristics. Through this review, the main aspects involved in the winemaking technology of sherry wines, and the latest scientific findings related to the microbiota of the flor film and other aspects associated to the changes in their chemical and sensory composition during aging will be revised. Some new trends in sherry wine technology focused on the acceleration of the biological aging or the use of organic grapes will be also considered.