Dimethyl Sulfide (DMS) in Amarone Wines: Influence of Aging, Withering, Grape Variety, and Geographical Origin.

Occurrence of dimethyl sulfide (DMS), a potent aroma compound accumulating during aging, was investigated in commercial and experimental Amarone wines. In commercial Amarone, DMS was observed in concentrations ranging from 2.9 to 64.3 µg/L. Model aging studies on experimental wines indicated that DMS in Amarone is strongly associated with aging and that wines from different vineyards can vary significantly in their ability to accumulate DMS during aging. The capacity of certain vineyards to give wines with higher DMS-forming potential was consistent across three consecutive vintages, representing a true terroir factor to be expressed with aging. Wine content of primary amino acids (PAN), a commonly analyzed enological parameter of grape must, was shown to be positively correlated with DMS accumulation during aging. Grape withering also increased DMS-forming potential mostly due to increased PAN resulting from concentration due to water loss. Increased pH due to withering also contributed to a higher DMS content of withered wines, but to a lower extent. In certain vineyard sites, an influence of vintage conditions on DMS-forming potential was also observed.

From bioprotective effects to diversification of wine aroma: Expanding the knowledge on Metschnikowia pulcherrima oenological potential.

Microbial diseases are of major concern in vitiviniculture as they cause grape losses and wine alterations, but the prevention with chemical substances represents a risk to human health and agricultural ecosystem. A promising alternative is the biocontrol and bioprotection activity of non-Saccharomyces yeasts, such as Metschnikowia pulcherrima, which also presents positive oenological traits when used in multistarter fermentations. The aim of this study was to assess the impact of a selected M. pulcherrima strain in the post-harvest withering and vinification of Garganega grapes to produce the sweet 'passito' wine Recioto di Gambellara DOCG (Italy). M. pulcherrima was firstly inoculated on grape at the beginning of the withering process, and afterwards in must for multistarter sequential microfermentation trials with Saccharomyces cerevisiae. Microbiological, chemical, and sensory analyses were carried out to monitor the vinification of treated and control grapes. Grape bunches during withering were a suitable environment for the colonization by M. pulcherrima, which effectively prevented growth of molds. Differences in grape must composition were observed, and the diverse inoculation strategies caused noticeable variations of fermentation kinetics, main oenological parameters, wine aroma profile, and sensory perception. M. pulcherrima proved effective to protect grapes against fungal infections during withering and contribute to alcoholic fermentation generating wine with distinguished aromatic characteristics.

Contribution of terpenes, methanethiol, and fermentative esters to sparkling wine aroma in relation to production technology, vintage, and aging: a case study on Durello wines.

BACKGROUND: The present study aimed to assess the chemical and sensory variability existing across sparkling white wines of a single appellation in relation to production technique and aging, identifying the existence of specific aroma chemical and sensory (odor) signatures. For this purpose, we selected Durello, an emerging sparkling white wine from the Veneto region produced using either Charmat or Classico methods. RESULTS: Comparison of Durello varietal volatiles profile with other Italian sparkling and still wines highlighted specific features of Durello, such as high content of 1,4-cineole and non-megastigmane norisoprenoids. The production technique (Charmat or Champenoise) impacted both the volatile chemical profile, influencing the content of esters, fatty acids, cyclic terpenoids, C6 alcohols, ß-damascenone and methanethiol. With regard to wine age and vintage, an influence on esters, p-menthane-1,8-diol, cineoles and methyl salicylate was observed. CONCLUSION: Sensory evaluation by means of a sorting task approach indicated the existence of two main types of odor profile, one clearly associated with Classico method. The main drivers of such aroma diversity were esters, 1,4-cineole and methanethiol. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Temperature affects organic acid, terpene and stilbene metabolisms in wine grapes during postharvest dehydration.

The partial dehydration of grapes after harvest is a traditional practice in several winegrowing regions that leads to the production of high quality wines. Postharvest dehydration (also known as withering) has a significant impact on the overall metabolism and physiology of the berry, yielding a final product that is richer in sugars, solutes, and aroma compounds. These changes are, at least in part, the result of a stress response, which is controlled at transcriptional level, and are highly dependent on the grape water loss kinetics and the environmental parameters of the facility where grapes are stored to wither. However, it is difficult to separate the effects driven by each single environmental factor from those of the dehydration rate, especially discerning the effect of temperature that greatly affects the water loss kinetics. To define the temperature influence on grape physiology and composition during postharvest dehydration, the withering of the red-skin grape cultivar Corvina (Vitis vinifera) was studied in two conditioned rooms set at distinct temperatures and at varying relative humidity to maintain an equal grape water loss rate. The effect of temperature was also studied by withering the grapes in two unconditioned facilities located in geographic areas with divergent climates. Technological, LC-MS and GC-MS analyses revealed higher levels of organic acids, flavonols, terpenes and cis- and trans-resveratrol in the grapes withered at lower temperature conditions, whereas higher concentrations of oligomeric stilbenes were found in the grapes stored at higher temperatures. Lower expression of the malate dehydrogenase and laccase, while higher expression of the phenylalanine ammonia-lyase, stilbene synthase and terpene synthase genes were detected in the grapes withered at lower temperatures. Our findings provide insights into the importance of the temperature in postharvest withering and its effect on the metabolism of the grapes and on the quality of the derived wines.

Reconstruction of Simplified Microbial Consortia to Modulate Sensory Quality of Kombucha Tea.

Kombucha is a fermented tea with a long history of production and consumption. It has been gaining popularity thanks to its refreshing taste and assumed beneficial properties. The microbial community responsible for tea fermentation-acetic acid bacteria (AAB), yeasts, and lactic acid bacteria (LAB)-is mainly found embedded in an extracellular cellulosic matrix located at the liquid-air interphase. To optimize the production process and investigate the contribution of individual strains, a collection of 26 unique strains was established from an artisanal-scale kombucha production; it included 13 AAB, 12 yeasts, and one LAB. Among these, distinctive strains, namely Novacetimonas hansenii T7SS-4G1, Brettanomyces bruxellensis T7SB-5W6, and Zygosaccharomyces parabailii T7SS-4W1, were used in mono- and co-culture fermentations. The monocultures highlighted important species-specific differences in the metabolism of sugars and organic acids, while binary co-cultures demonstrated the roles played by bacteria and yeasts in the production of cellulose and typical volatile acidity. Aroma complexity and sensory perception were comparable between reconstructed (with the three strains) and native microbial consortia. This study provided a broad picture of the strains' metabolic signatures, facilitating the standardization of kombucha production in order to obtain a product with desired characteristics by modulating strains presence or abundance.

The contribution of varietal thiols in the diverse aroma of Italian monovarietal white wines.

Thanks to their low odor detection thresholds, free varietal thiols (VTs) play a key role in the primary aroma of wines, to which they confer an intense scent reminiscent of box tree, grapefruit, citrus fruits, passionfruit and cat urine odor. Excluding wines from a few VT-rich grapevine cultivars, VTs appear to be present in most cultivars at trace levels, although a comprehensive dataset is still missing. The low concentration of VTs combined with their high reactivity and matrix complexity make their determination in wines a challenging task. In this research an optimized liquid chromatography - tandem mass spectrometry (LC-MS/MS) method was validated and used for the quantification of 4-methyl-4-sulfanylpentan-2-one (4-MSP), 3-sulfanylhexan-1-ol (3-SH), 3-sulfanylhexyl acetate (3-SHA) and ethyl 3-sulfanylpropionate (E3SP) in 246 samples (vintage 2019) representative of 18 monovarietal Italian white wines. VTs were detected in all cultivars even though higher values of 3-SH were found in Lugana, Müller-Thurgau and Verdicchio cultivars. Müller-Thurgau wines showed the highest level of 4-MSP, that was mainly correlated to the odor descriptors of passionfruit and box tree/cat urine. The VTs composition of Müller-Thurgau was confirmed on a second set of 50 wines from different vintages. From a sensory perspective, the samples of Müller-Thurgau showed the best positive correlations between chemical variables and the odor descriptors thiol note, passion fruit and box tree/cat urine. These notes are significantly related to 4-MSP, suggesting that it could play a relevant olfactory role for the aroma of Müller-Thurgau wines. Sorting analysis allowed to group these wines according to their thiolic characteristics. The chemical variables and the odor descriptors attributable to the thiol notes are important for Müller-Thurgau and Lugana wines, while the contribution of thiol notes was sensorially negligible for the other wines.

Volatile Compounds in Monovarietal Wines of Two Amarone Della Valpolicella Terroirs: Chemical and Sensory Impact of Grape Variety and Origin, Yeast Strain and Spontaneous Fermentation.

Aroma profiles of withered Corvina and Corvinone wines from two different Valpolicella terroirs were investigated in relationship to yeast strain and use of spontaneous fermentation. The results indicated that volatile chemical differences between wines were mainly driven by grape origin, which was associated with distinctive compositional profiles. Wine content in terpenes, norisoprenoids, benzenoids and C6 alcohols, as well as some fermentative esters, were indeed significantly affected by grape origin. Conversely, yeast strain influence was mainly associated with fermentation-derived esters. Sensory analysis, besides confirming the major role of grape origin as driver of wine differentiation, indicated that spontaneous fermentations reduced the sensory differences associated with grape origin and variety, mainly due to high content of acetic acid and ethyl acetate.

Two Sides to One Story-Aroma Chemical and Sensory Signature of Lugana and Verdicchio Wines.

Lugana and Verdicchio are two Italian white wines with a Protected Designation of Origin (PDO) label. These two wine types are produced in different regions using the same grape variety. The aim of this work is to investigate the existence of volatile chemical markers that could help to elucidate differences between Lugana and Verdicchio wines both at chemical and sensory levels. Thirteen commercial wine samples were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS), and 76 volatile compounds were identified and quantified. Verdicchio and Lugana had been differentiated on the basis of 19 free and glycosidically bound compounds belonging to the chemical classes of terpenes, benzenoids, higher alcohols, C6 alcohols and norisoprenoids. Samples were assessed by means of a sorting task sensory analysis, resulting in two clusters formed. These results suggested the existence of 2 product types with specific sensory spaces that can be related, to a good extend, to Verdicchio and Lugana wines. Cluster 1 was composed of six wines, 4 of which were Lugana, while Cluster 2 was formed of 7 wines, 5 of which were Verdicchio. The first cluster was described as "fruity", and "fresh/minty", while the second as "fermentative" and "spicy". An attempt was made to relate analytical and sensory data, the results showed that damascenone and the sum of 3 of esters the ethyl hexanoate, ethyl octanoate and isoamyl acetate, was characterizing Cluster 1. These results highlighted the primary importance of geographical origin to the volatile composition and perceived aroma of Lugana and Verdicchio wines.

Influence of Different Modalities of Grape Withering on Volatile Compounds of Young and Aged Corvina Wines.

Withering is a practice traditionally used in various regions to produce sweet or dry wines. During withering there is an increase in sugar content but also a modification in volatile compound profiles. Controlling metabolic changes through the dehydration process to obtain wines with desired characteristics is therefore a challenging opportunity. The effects of two different withering technologies, post-harvest or on-vine with blocked sap vessel flow, on the volatile profile of young and aged Corvina red wines was investigated. The results showed that modulation of wine aroma due to the withering process is associated with fermentative metabolites, such as esters, higher alcohols, and acids, as well as grape-related compounds such as C6 alcohols, terpenes and norisoprenoids. Significant differences were also found by comparing the two withering techniques. Post-harvest in a traditional "fruttaio" warehouse wines showed higher content of ethyl acetate, ethyl butanoate, ß-citronellol and 3-oxo-α-ionol, whereas post-harvest withering on-vine increased ß-damascenone in wines. The type of withering technique has an influence on the evolution of some aroma compounds during the aging of wine, among them linalool, (E)-1-(2,3,6-trimethylphenyl)buta-1,3-diene (TPB), n-hexyl acetate, ethyl acetate, ethyl 3-methylbutanoate, 3-oxo-α-ionol and ß-damascenone.

Fate of Grape-Derived Terpenoids in Model Systems Containing Active Yeast Cells.

Terpenes are important contributors to wine aroma. Free and glycosidically bound terpenes are primarily formed in grapes. During fermentation, they undergo important transformation catalyzed by yeast, so that the terpene profile of grape is substantially different from that of the corresponding wine. The present paper assessed the ability of a Saccharomyces cerevisiae strain to transform 17 different terpenes. Biotransformation was performed by placing target compounds in incubation with resting cells. Volatile compounds produced were extracted by solid-phase extraction and analyzed by gas chromatography-mass spectrometry. Geranyl acetate, neryl acetate, citronellyl acetate, and menthyl acetate were formed from the corresponding terpene alcohols. ß-Citronellol was the main product of geraniol transformation; geranial, an intermediate of this pathway, has also been detected. Limonene was hydroxylated by yeast to form carveol, trans-2,8-menthadien-1-ol, and cis-2,8-menthadien-1-ol. Moreover, yeast cells were found to be able to adsorb a significant portion of the terpenes present in the reaction batches, with the extent of this phenomenon being linked to terpene hydrophobicity.

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.