Microbiota and metabolites of aged bottled gueuze beers converge to the same composition.

Gueuze beers are prepared by mixing young and old lambic beers and are bottle-refermented spontaneously for aging. The present study analyzed the microbiota and metabolites present in gueuze beers that were aged between a few months and up to 17 years. Yeasts were cultivated from all beers sampled, but bacteria could not be grown from beers older than 5 years. Lactic acid and ethyl lactate concentrations increased steadily during aging, whereas ethanol concentrations remained constant. The concentrations of isoamyl acetate and ethyl decanoate decreased during the aging process. Hence, ethyl lactate and ethyl decanoate can be considered as positive and negative gueuze beer-aging metabolite biomarkers, respectively. Nevertheless, considerable bottle-to-bottle variation in the metabolite profiles was found, which hindered the generalization of the effects seen during the aging of the gueuze beers examined, but which illustrated the unique character of the lambic beers. The present results further indicate that gueuze beers are preferably aged for less than 10 years.

Characterization of volatile compounds and sensory properties of spine grape (Vitis davidii Foex) brandies aged with different toasted wood chips.

Aging is an important process for improving wine and brandy quality. In this study, the chemical characterization and sensory properties of spine grape brandies were compared after aging with various species of wood chips, including French oak (FO), American oak (AO), Mongolian oak (MO), Japanese blue oak (JO), chestnut, catalpa, and cherry. The results showed that high color intensity and significant concentrations of tannins and polyphenols were observed in the brandies aged with FO, AO, and chestnut chips. The volatile compounds, such as ethyl decanoate, ethyl 2-methylbutanoate, ethyl octanoate, methyl salicylate, (Z)-2-hexenol, and furfural, contributed to the floral, fruity, and roasted/smoky attributes of the brandies aged with FO, AO, and chestnut chips. The 1-butanol, 1-propanol, phenylethanol, phenylethyl acetate, isoamyl acetate, and linalool contributed to the fruity, honey, and floral attributes of the brandies aged with JO and cherry chips. These findings are extremely useful for the production of differentiated and high-quality spine grape brandies.

Improving flavor of summer Keemun black tea by solid-state fermentation using Cordyceps militaris revealed by LC/MS-based metabolomics and GC/MS analysis.

Cordyceps militaris (C. militaris) has been approved and widely used in healthy food. The present study aimed to improve the flavor of summer Keemun black tea (KBT) using C. militaris solid-state fermentation. Combined with sensory evaluation, the volatile and non-volatile components of solid-state fermentation of KBT (SSF-KBT) and KBT were analyzed. The results showed that after the solid-state fermentation, the contents of total polyphenol, total flavonoid, and total free amino acids were significantly reduced. Further non-targeted metabolomics analysis revealed that the contents of non-galloylated catechins and d-mannitol increased, while the galloylated catechins and flavonoid glycosides decreased as did the bitterness and astringency of KBT. Dihydro-ß-ionone and ß-ionone (OAV = 59321.97 and 8154.17) were the aroma-active compounds imparting woody and floral odors in SSF-KBT, respectively. Current study provides a new avenue to develop summer-autumn KBT.

Adjustment of impact odorants in Hutai-8 rose wine by co-fermentation of Pichia fermentans and Saccharomyces cerevisiae.

Hutai-8 grape (Vitis vinifera × Vitis labrusca) was fermented into rose wine with Saccharomyces cerevisiae to characterize the key aroma compounds by sensomics approach, and fermented with selected Pichia fermentans and S. cerevisiae for aroma enhancement. In total, 82 odorants were detected in single-fermentation Hutai-8 rose wine, 22 aroma active compounds, mainly varietal odorants and fruity esters, were further quantitated for aroma reconstitution tests, and successfully mimicked sweet, floral, and fruity traits. Omission tests excluded the importance of isobutyl acetate, ethyl butyrate, 1-nonanol for aroma development. Furthermore, the successfully recombined co-fermentation Hutai-8 rose wine revealed 21 aroma active compounds identified from 79 odorants. The complexity of wine fruity/floral characteristics was improved through increased levels of inactive odorants and decreased levels of off-odorants. Moreover, rose wine made by co-inoculation had greater color stability compared to single-fermentation. This work provides insights into the understanding of mechanisms underlying modulation of co-fermentation for improved wine quality.

Aromatic, olfactometric and consumer description of sweet ciders obtained by cryo-extraction.

Nine ciders obtained by cryo-extraction were analysed for chemical, olfactometric and sensory characteristics. Three types of ice apple juices and three autochthonous yeast strains were evaluated. The quantitative volatile profile is mainly influenced by the apple juice. Regarding the olfactometric profiles of the ice ciders, 23 odorants not previously found in Spanish still ciders, and described as sweet, spicy, fruity and floral were observed. Among these, it is worth mentioning 5 high-boiling point compounds found in an olfactometric zone where heavy, phenolic odours predominate in still ciders. The sensory descriptions obtained by Check-All-That-Apply classified the ice ciders mainly by their sweet taste and smoothness, these attributes being the most influential in the assessment of the overall quality of the ciders. The most highly valued ciders were described as the sweetest, most fruity ones, in agreement with their having the highest values for the ratio between total sugars and total acidity.

Changes in volatile compounds of grape pomace distillate (Italian grappa) during one-year ageing in oak and cherry barrels.

The Italian grape pomace distillate grappa is often refined by ageing in wooden barrels. Chemical changes of the volatile profile of two samples produced from a Cabernet Sauvignon/Merlot blend and Prosecco pomace both at two ethanol contents (55% and 68%) were studied during one-year ageing in cherry and oak barriques. Grappa variety, ethanol content and barrel type strongly affected the volatiles profile of the distillates. Oak-aged grappa contained 10-fold the wood volatiles of the cherry-aged one, but the latter had higher levels of syringaldehyde, coniferaldehyde, and 3,4,5-trimethoxyphenol; 55% ethanol extracted higher levels of wood compounds and ethoxy-compounds were higher in the 68%-ethanol distillates. Prosecco grappa extracted higher wood compounds and showed no significant changes in the levels of fruity/floral esters and terpenols. Findings of this study can be also useful in the development of new ageing processes of distillates for which cherry barrels are still not used (e.g., brandy and whisky).

Fine tuning of medium chain fatty acids levels increases fruity ester production during alcoholic fermentation.

Pichia fermentans Z9Y-3 and its intracellular enzymes were inoculated along with S. cerevisiae in synthetic grape must to modulate fruity ester production. The levels of ester-related enzymes, ester precursors, and fruity esters were monitored every 24 h during fermentation. Results showed that the levels of ethyl acetate, acetate higher alcohol esters (AHEs), short chain fatty acid ethyl esters (SFEs), and medium chain fatty acid ethyl esters (MFEs) were significantly enhanced in mixed fermentation. Pearson correlation analysis further revealed that higher alcohols and fatty acids played a more important role in fruity ester production than enzymes; Particularly, the correlation coefficient between fatty acids and MFEs was 0.940. In addition, supplementation of medium chain fatty acids (7.2 mg/L) at the metaphase of single S. cerevisiae fermentation improved ethyl acetate, AHE, SFE, and MFE production by 42.56%, 21.00%, 61.33%, and 90.04%, respectively, although the high level of ethyl acetate might result in off-flavors.

Using an electronic nose and volatilome analysis to differentiate sparkling wines obtained under different conditions of temperature, ageing time and yeast formats.

Effect of yeast inoculation format (F), temperature (T), and "on lees" ageing time (t) factors were evaluated on the composition of sparkling wines by a quantitative fingerprint obtained from volatile metabolites and the response of an electronic nose (E-nose). Wines elaborated according the traditional method at 10 and 14 °C, free cells and yeast biocapsules formats were monitored at 15 and 24 months of ageing time. Sixty-six volatiles identified and quantified in the eight sampling lots were subjected to a pattern recognition technique. A dual criterion based on univariate (ANOVA) and multivariate analysis (PLS-DA) through the variable importance projection (VIP) values, allowed to identify ten volatiles as potential markers for T factor, eleven for t and twelve for F factors. The discriminant models based on E-nose dataset enable a 100% correct classification of samples, in relation with t and F factors and the 83% for T factor.

Multivariate analysis reveals effect of glutathione-enriched inactive dry yeast on amino acids and volatile components of kiwi wine.

Principal component analysis (PCA) and partial least squares (PLS) regression were applied to investigate the effect of glutathione-enriched inactive dry yeast (g-IDY) on the amino acids and volatile components of kiwi wine. Results indicated that the addition of g-IDY had positive effect on most amino acids of kiwi wine, especially glutamine and glycine. In case of pure juice fermentation, the concentrations of ethyl decanoate, 2-methylbutyric acid, trans-2-nonenal and hexyl butyrate had notably positive correlation with the addition of g-IDY. PLS regression indicated that the amino acids were highly interrelated to the volatile compositions, and glycine had the strongest positive impact on the concentrations of esters and total volatile components. This might explain the similar effect of g-IDY on the amino acids and volatile components of kiwi wine. Besides, PLS regression showed that E-nose was a good method to predict volatile compositions of kiwi wine, especially esters.

Characteristics of ice juices and ciders made by cryo-extraction with different cider apple varieties and yeast strains.

Two sets of nine ciders were made by cryo-extraction for two consecutive harvests combining three types of ice cider apple juices (mono-varietal, bi-varietal and multi-varietal) and three autochthonous Saccharomyces bayanus yeast strains. The type of juice significantly influenced the pH values and the contents of sorbitol and shikimic acid in the ice juices. The strains used as starters did develop the fermentation producing ciders with alcoholic degrees between 8.75 and 11.52 (% v/v) and volatile acidities lower than 0.55 g acetic acid/L. Regarding the ice ciders, the apple mixture significantly influenced the levels of methanol (higher in mono-varietal ciders), 2-phenylethanol, and some minor acetate esters (higher in the bi-varietal ciders). The last ciders were also more floral, buttery, acidic and bitter than those made from mono- and multi-varietal juices. In the first harvest, the ciders obtained from the bi-varietal apple mixture scored lower for overall sensory quality.

Use of a flor yeast strain for the second fermentation of sparkling wines: Effect of endogenous CO2 over-pressure on the volatilome.

Saccharomyces cerevisiae flor yeast is used for the first time in sparkling wine-making. Twenty-six oenological variables and fifty-three volatile metabolites are quantified in the middle (P = 3 bar) and at the end (P = 6 bar) of the second fermentation, carried out in open and closed bottles. A heat-map of volatiles and the fingerprints obtained for ten chemical families and ten odorant series visualize the changes for each condition. Terpenes, fatty acids and volatile phenols increased their contents by pressure effect at the end of the study by 25.0, 7.8 and 2.2%, respectively. The remaining families decrease between 17.4% and 30.1% for furanic compounds and esters in the same stage. A Principal Component Analysis established that nine volatiles are mainly affected by pressure and five by fermentation stage. The use of ethanol-tolerant flor yeasts constitutes an innovative procedure for the enhancement of the sparkling wines diversification.

Enhancing wine ester biosynthesis in mixed Hanseniaspora uvarum/Saccharomyces cerevisiae fermentation by nitrogen nutrient addition.

The dynamic changes of wine ester production during mixed fermentation with Hanseniaspora uvarum Yun268 and Saccharomyces cerevisiae F5 was investigated at different levels and timings of nitrogen nutrient addition. Nitrogen additions were performed by supplementing yeast assimilable nitrogen (YAN) into a synthetic grape must with defined composition. Ester precursors and extracellular metabolites involved in ester synthesis were analyzed throughout the fermentation. Results showed that nitrogen additions covering 50-200 mg/L YAN at the point of yeast inoculation slightly affected yeast competition and ester profiles. Interestingly, when YAN was supplemented in the mid-stage, the survival of H. uvarum Yun268 was enhanced, resulting in more than a 2-fold increase in the levels of higher alcohol acetates compared to that at the initial stage. Furthermore, carbon fluxes may be redistributed in the central pathway, which contributed to the production of medium-chain fatty acids and eventually triggered a 1.2-fold elevation in corresponding ethyl ester levels.

Increase of medium-chain fatty acid ethyl ester content in mixed H. uvarum/S. cerevisiae fermentation leads to wine fruity aroma enhancement.

Medium-chain fatty acid (MCFA) ethyl esters, as yeast secondary metabolites, significantly contribute to the fruity aroma of foods and beverages. To improve the MCFA ethyl ester content of wine, mixed fermentations with Hanseniaspora uvarum Yun268 and Saccharomyces cerevisiae were performed. Final volatiles were analyzed by gas solid phase microextraction-chromatography-mass spectrometry, and aroma characteristics were quantitated by sensory analysis. Results showed that mixed fermentation increased MCFA ethyl ester content by 37% in Cabernet Gernischt wine compared to that obtained by pure fermentation. Partial least-squares regression analysis further revealed that the improved MCFA ethyl esters specifically enhanced the temperate fruity aroma of wine. The enhancement of MCFA ethyl esters was attributed to the increased contents of MCFAs that could be induced by the presence of H. uvarum Yun268 in mixed fermentation. Meanwhile, the timing of yeast inoculations significantly affected the involving biomass of each strain and the dynamics of ethanol accumulation.

Chemical consequences of three commercial strains of Oenococcus oeni co-inoculated with Torulaspora delbrueckii in durian wine fermentation.

This work evaluated for the first time the chemical consequences of three commercial strains of Oenococcus oeni co-inoculated with Torulaspora delbrueckii in durian wine fermentation. Compared with the control (yeast only, 5.70% v/v ethanol produced), samples co-inoculated with T. delbrueckii and O. oeni PN4 improved ethanol production (6.06% v/v), which was significantly higher than samples co-inoculated with Viniflora (4.78% v/v) or Enoferm Beta (5.01% v/v). Wines co-fermented with the respective latter two oenococci contained excessive levels of ethyl acetate (>80mg/L) that were likely to affect negatively wine aroma. In addition, they led to significantly higher acetic and lactic acid production relative to PN4. O. oeni PN4 seemed to be the most suitable strain to co-inoculate with T. delbrueckii for simultaneous alcoholic and malolactic fermentation in durian wine by contributing moderately increased concentrations of higher alcohols, acetate esters and ethyl esters that would have positive sensory impacts.

Effect of curing salts and probiotic cultures on the evolution of flavor compounds in dry-fermented sausages during ripening.

The effect of the concentration of curing salts, the nature of the probiotic culture (free or immobilized Lactobacillus casei ATCC 393 on wheat grains) and the ripening time on the generation of volatile compounds in probiotic dry-fermented sausages was investigated. Samples were collected after 1, 28 and 71 days of ripening and subjected to SPME GC/MS analysis. All factors affected significantly the concentration of all volatile compounds. Noticeably, the content of esters, organic acids and total volatiles was significantly increased after 28 and 71 days of ripening in almost all products. In most cases, reduction of curing salts content resulted in significant increase of esters and organic acids during ripening, whereas the opposite effect was observed in carbonyl compounds at days 28 and 71. Principal Component Analysis of the semi-quantitative data revealed that primarily the ripening process affected the volatile composition.

Chemical and sensory profiles of rosé wines from Australia.

The appeal of rosé wine is attributable to its sensory profiles and underlying chemical composition, which are determined by viticultural and oenological inputs. This study provided the first insight into the sensory attributes and volatile profiles of Australian rosé wines. An HS-SPME-GC-MS method and a recently developed HPLC-MS/MS method were used to quantify 51 volatile compounds, including 4 potent sulfur compounds, in 26 commercial rosé wines. Descriptive analysis on all wines was undertaken and the sensory results were correlated with quantitative chemical data to explore relationships between wine composition and sensory profiles. Based on odour activity values, esters were prominent aroma volatiles, and ß-damascenone, 3-methylbutyl acetate, ethyl hexanoate and 3-MHA were deemed to be important, in accord with other studies. Wines were described with terms ranging from developed, spicy and savoury to fresh green, citrus, tropical fruit, floral and confectionery.

Selection of aroma compounds for the differentiation of wines obtained by fermenting musts with starter cultures of commercial yeast strains.

Nine wines obtained by fermenting Aligoté musts with individual starter cultures of eight Saccharomyces cerevisiae yeast strains and with the indigenous microbiota were compared in terms of their composition in minor volatile aroma compounds. An easy handle methodology Stir-Bar-Sorptive-Adsorption, Gas Chromatography-Mass Spectrometry based, permits the identification of 49 aroma compounds. The rearrangement of these aroma compounds in six chemical families permits the establishment of a finger printing for each wine. Eighteen aroma compounds that exhibit a high differentiation power (p⩽0.05) were selected for chemometric analysis. The Principal Component Analysis carried out with these aroma compounds reveal that the first two principal components explain 53.8% and 17.2% of the total variance, respectively, allowing the establishment of nine different groups, in accordance with the wine types obtained. These results reveal analytical differences among the wines that are not recognized by sensorial analysis.