The most mysterious aspect of wine is the endless variety of flavours that stem from a complex, completely non-linear system of interactions among many hundreds of compounds. In its widest sense, wine flavour refers to the overall impression of both aroma and taste components. Aroma is usually associated with odorous, volatile compounds; the bouquet of wine refers to the more complex flavour compounds which evolve as a result of fermentation, elevage and ageing. With the exception of terpenes in the aromatic grape varieties and alkoxypyrazines in the herbaceous cultivars, perceived flavour is the result of absolute amounts and specific ratios of many of these interactive compounds, rather than being attributable to a single "impact" compound. Without underestimating the complexity of these interactive effects or negating the definitive role played by the accumulated secondary grape metabolites in the varietal character of wine, this review will focus mainly on the contribution of yeast fermentation to the sensorial quality of the final product. Yeast and fermentation conditions are claimed to be the most important factors influencing the flavours in wine. Both spontaneous and inoculated wine fermentations are affected by the diversity of yeasts associated with the vineyard and winery. During the primary alcoholic fermentation of sugar, the wine yeast, Saccharomyces cerevisiae, together with other indigenous non-Saccharomyces species, produce ethanol, carbon dioxide and a number of by-products. Of these yeast-derived metabolites, the alcohols, acetates and C4-C8 1tfatty acid ethyl esters are found in the highest concentration in wine. While the volatile metabolites contribute to the fermentation bouquet ubiquitous to all young wines, the production levels of these by-products are variable and yeast strain specific. Therefore, this article also highlights the importance of untapping the hidden wealth of indigenous yeast species present on grapes, and the selection and genetic development of yeast starter culture strains with improved flavour profiles. In the future, some winemakers may prefer to use mixtures of indigenous yeast species and tailored S. cerevisiae strains as starter cultures to reflect the biodiversity and stylistic distinctiveness of a given region. This will help winemakers to fullfil the consumer's demand for individual wines with intact local character and to ensure the survival of wine's most enthralling aspect - its endless variety.

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Yeast and its Importance to Wine Aroma - A Review

Aroma compounds in Chinese “Wuliangye” liquor were identified by gas chromatography−olfactometry (GC−O) after fractionation. A total of 132 odorants were detected by GC−O in Wuliangye liquor on DB-wax and DB-5 columns. Of these, 126 aromas were identified by GC−mass spectrometry (MS). Aroma extract dilution analysis (AEDA) was further employed to identify the most important aroma compounds in “Wuliangye” and “Jiannanchun” liquors. The results showed that esters could be the most important class, especially ethyl esters. Various alcohols, aldehydes, acetals, alkylpyrazines, furan derivatives, lactones, and sulfur-containing and phenolic compounds were also found to be important. On the basis of flavor dilution (FD) values, the most important aroma compounds in Wuliangye and Jiannanchun liquors could be ethyl butanoate, ethyl pentanoate, ethyl hexanoate, ethyl octanoate, butyl hexanoate, ethyl 3-methylbutanoate, hexanoic acid, and 1,1-diethoxy-3-methylbutane (FD ≥ 1024). These compounds contributed to fruit...

Characterization of aroma compounds of chinese "Wuliangye" and "Jiannanchun" liquors by aroma extract dilution analysis.

The aroma compounds of young and aged Chinese “Yanghe Daqu” liquor samples were extracted by solid phase microextraction (SPME) and analyzed by gas chromatography (GC)−olfactometry dilution analysis. The original liquor samples were diluted with deionized water to give a final alcohol content of 14% (v/v). The samples were stepwise diluted (1:1) with 14% (by volume) ethanol−water solution and then extracted by headspace SPME. The samples were preequilibrated at 50 °C for 15 min and extracted with stirring at the same temperature for 30 min prior to injection into GC. The aroma compounds were identified by both GC-MS and GC−olfactometry using DB-Wax and DB-5 columns. The results suggested that esters were the major contributors to Yanghe Daqu liquor aroma. Ethyl hexanoate, ethyl butanoate, and ethyl pentanoate had very high flavor dilution values in both young and aged liquors (FD > 8192). Methyl hexanoate, ethyl heptanoate, ethyl benzoate, and butyl hexanoate could also be very important because of their ...

Headspace Solid Phase Microextraction and Gas Chromatography−Olfactometry Dilution Analysis of Young and Aged Chinese “Yanghe Daqu” Liquors

Sensory properties and aroma compounds of sweet Fiano wine

Membrane technology for the processing of fruit juices and beverages has been applied mainly for clarification using ultrafiltration and microfiltration, and for concentration using reverse osmosis. The effects of product preparation, membrane selection, and operating parameters are important factors influencing filtration rate and product quality. Technological advances related to the development of new membranes, improvement in process engineering, and better understanding of fruit beverage constituents have expanded the range of membrane separation processes. Developments in novel membrane processes, including electrodialysis and pervaporation, increased the array of applications in combination with other technologies for alternate uses in fruit juices and beverages.

Membrane processing of fruit juices and beverages: a review.

In wine making, the bacteriolytic activity of lysozyme has primarily been used to control the malolactic fermentation in wines. The use of lysozyme in musts before settling and the beginning of the alcoholic fermentation to inhibit the growth of lactic acid bacteria could be very beneficial. In a resistance test carried out in MT/b broth, lysozyme had greater antimicrobial activity toward Oenococcus oeni than Lactobacillus species. Several strains of wine bacteria belonging to Oenococcus proved sensitive to the bacteriolytic activity of lysozyme at low concentrations in both synthetic medium (MT/b) (50 mg/L), white must, or red must made with or without the skins (100 mg/L). Lactobacillus and Pediococcus strains survived at lysozyme concentrations of 200−500 and 500 mg/L, respectively, in MT/b and musts. Suspended solids in unclarified musts may strongly bind to lysozyme thereby causing its removal by filtration or centrifugation. One hour after lysozyme was added to musts, it was quantified by HPLC and f...

Resistance Screening Essay of Wine Lactic Acid Bacteria on Lysozyme: Efficacy of Lysozyme in Unclarified Grape Musts

The capacity of 100 yeast strains - isolated from grape musts and wines from the Istituto Sperimentale per l'Enologia collection - to produce benzaldehyde, benzyl alcohol and benzoic acid was verified by inoculation into a synthetic nutrient medium (MNS). Schizosaccharomyces and Zygosaccharomyces were strongest in producing benzaldehyde (maximal amount found 1200 µg/l) and benzyl alcohol (maximally 523 µg/l). Zygosaccharomyces was also most effective in the production of benzoic acid (maximally 536 µg/l), followed by Saccharomyces, Cryptococcus, Kloeckera and Torulaspora. The hypothesis was verified that yeasts can be an exogenous source of the benzyl alcohol oxidizing enzyme in grape musts and wines. Wine yeast strains of Saccharomyces spp., Zygosaccharomyces spp. and Schizosaccharomyces spp. fermenting MNS containing 150 g/l glucose, with benzyl alcohol added, transformed this into benzoic acid only when glucose was disappearing, but not into benzaldehyde. No difference was observed between aerobic and anaerobic fermentation conditions. The uptake of benzyl alcohol was rapid in fermentation essays in presence of only 10 g/l glucose and in assimilation essais performed in yeast nitrogen base broth with assimilable carbon compounds added. A catabolic repression by glucose appears likely. Botrytis cinerea was able to transform benzyl alcohol into benzaldehyde and benzoic acid on Czapek-Dox broth with 30 g/l sucrose added. Benzyl alcohol was transformed by wine yeasts into benzoic acid when the concentration of glucose in the mineral medium was less than 10 g/l, but no production of benzaldehyde was observed. A catabolic repression of this transformation by glucose is likely. Botrytis cinerea was able to produce benzaldehyde in a mineral medium with benzyl alcohol and sucrose added.

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Production of benzaldehyde, benzyl alcohol and benzoic acid by yeasts and Botrytis cinerea isolated from grape musts and wines

A new rapid method to determine the total esterase enzymatic activity of yeast cells is proposed. In a sodium phosphate buffer a β-naphthol synthetic ester is hydrolized by cells, and the released β-naphthol is coupled with a diazonium salt (Fast Garnet GBC) in the presence of sodium dodecyl sulfate. The whole procedure is carried out in an aqueous buffer medium, and the resulting azo dye is directly evaluated by absorbance measurement at 524 nm. The analytical results from different assays were adjusted to a fixed cell concentration with a statistical procedure. The method shows good repeatability, reproducibility and detectability, and it requires simple equipment and instruments. It is therefore suitable both for routine analysis, as industrial yeast strain screening, and for yeast physiological studies, in order to improve the aromatic quality of fermented drinks.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1993.tb01177.x

A rapid spectrophotometric method to determine esterase activity of yeast cells in an aqueous medium

There are evidences that a grape must of a non aromatic vine, not having perfume and revealing by gaschromatographie only some classes of compounds common to the musts of all the vine varieties, can originate a pool of characterizing fragrant substances after contact with the yeast during fermentation. Therefore, despite the scarce scientific knowledge available on biochemical mechanisms involved in Saccharomyces cerevisiae in the formation of a wine aromatic pattern, it can be likely hypothesized that the yeast could be the biological motor of this aromatic transformation. The yeast can act on the compounds of the must with many periplasmic enzymes (esterases, glycosidases, lyases, lipases, proteases, peptidases, pectolytiques) and several are the scientific contributions underlining the existence of an interaction between the yeast and the vine variety in the formation of wine aromatic characteristics. Besides the individual contribution of substances sensorially active, the yeast would contribute to the transformation of unknown varietal aromatic precursors that are in the grape skins and/or musts. The biochemical, genetic and physiological aspects of this transformation still have to be understood. At the end, we have to answer some important questions such as the mutual role that grape and/or yeast enzymes have during and soon after crushing in the liberation of the varietal precursors and in the conversion of these in fragrant compounds.

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A review. Biochemical and molecular mechanisms in Saccharomyces cerevisiae that are involved in the formation of some volatile compounds in wines

Pendant les vendanges 1988 et 1989, les auteurs ont procede a des essais d'enrichissement par osmose inverse et par addition de mout concentre rectifie sur 9 varietes differentes de mout (Barbera, Cabernet, Chardonnay, Cortese, Muscat, Pinot, Riesling, Schiava, Nebbiolo), en prenant comme base un mout brut. L'appareillage employe a ete fabrique par la SNAMPROGETTI BIOTECNOLOGIE et peut traiter 100 hl par heure.L'analyse de la composition des mouts a demontre une augmentation du degre sucre, de l'extrait net, des cendres, de l'alcalinite des cendres et de l'acidite totale en fonction du pourcentage d'eau enlevee. L'acidite totale se reequilibre lors de la vinification surtout au niveau des sels d'acide tartrique. Le pH reste a peu pres identique dans les 3 lots de mout compares. Les permeats, diffuses au travers des membranes ne presentent pas ou peu de composes presents dans le mout frais. Pour la vinification des vins rouges, il est necessaire d'equilibrer les substances en exces dues au rapport pellicules/mout par effet de la concentration par osmose inverse. Aucune perte en substances colorantes n'a ete observee pendant la concentration.Les resultats d'analyses chimiques et organoleptiques de vins obtenus indiquent que ceux traites par osmose inverse sont dans la plupart des cas nettement differents de ceux traites par addition de mout concentre rectifie et sont preferes a ceux non enrichis. Pour le Cortese de Gavi, l'echantillon enrichi par osmose inverse a ete nettement prefere a celui additionne de mout concentre rectifie, alors qu'aucun echantillon additionne de mout concentre rectifie n'a ete prefere par rapport a un echantillon "osmose inverse".

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Claudio Delfini

Papers

Resistance Screening Essay of Wine Lactic Acid Bacteria on Lysozyme: Efficacy of Lysozyme in Unclarified Grape Musts

Production of benzaldehyde, benzyl alcohol and benzoic acid by yeasts and Botrytis cinerea isolated from grape musts and wines

A rapid spectrophotometric method to determine esterase activity of yeast cells in an aqueous medium

A review. Biochemical and molecular mechanisms in Saccharomyces cerevisiae that are involved in the formation of some volatile compounds in wines

Essais d'enrichissement partiel de moût de raisin par osmose inverse