Wine is a highly complex mixture of compounds which largely define its appearance, aroma, flavour and mouth-feel properties. The compounds responsible for those attributes have been derived in turn from three major sources, viz. grapes, microbes and, when used, wood (most commonly, oak). The grape-derived compounds provide varietal distinction in addition to giving wine its basic structure. Thus, the floral monoterpenes largely define Muscat-related wines and the fruity volatile thiols define Sauvignon-related wines; the grape acids and tannins, together with alcohol, contribute the palate and mouth-feel properties. Yeast fermentation of sugars not only produces ethanol and carbon dioxide but a range of minor but sensorially important volatile metabolites which gives wine its vinous character. These volatile metabolites, which comprise esters, higher alcohols, carbonyls, volatile fatty acids and sulfur compounds, are derived from sugar and amino acid metabolism. The malolactic fermentation, when needed, not only provides deacidification, but can enhance the flavour profile.

The aroma and flavour profile of wine is the result of an almost infinite number of variations in production, whether in the vineyard or the winery. In addition to the obvious, such as the grapes selected, the winemaker employs a variety of techniques and tools to produce wines with specific flavour profiles. One of these tools is the choice of microorganism to conduct fermentation. During alcoholic fermentation, the wine yeast Saccharomyces cerevisiae brings forth the major changes between grape must and wine: modifying aroma, flavour, mouth-feel, colour and chemical complexity. The wine bacterium Oenococcus oeni adds its contribution to wines that undergo malolactic fermentation. Thus flavour-active yeasts and bacterial strains can produce desirable sensory results by helping to extract compounds from the solids in grape must, by modifying grape-derived molecules and by producing flavour-active metabolites. This article reviews some of the most important flavour compounds found in wine, and their microbiological origin.

Yeast and bacterial modulation of wine aroma and flavour

Fifty-two young monovarietal red wines made with Grenache (17 samples), Tempranillo (11 samples), Cabernet Sauvignon (12 samples) and Merlot (12 samples) grapes have been analysed by HRGC–MS to obtain quantitative data on 47 odorants previously identified as potential aroma contributors by olfactometric techniques. Thirty-three odorants were present in the wines at concentrations higher than their corresponding odour thresholds. These include ethyl octanoate, β-damascenone, ethyl hexanoate, isovaleric acid and isoamyl acetate as the most important, which together with isoamyl and β-phenylethyl alcohols, fatty acids, 2,3-butanedione and ethyl butyrate are always found at concentrations higher than their odour thresholds. In some cases the ethyl esters of isobutyric and isovaleric acids, β-ionone, methionol, isobutyric acid, ethyl cinnamate, ethyl dihydrocinnamate, γ-nonalactone, eugenol, c-3-hexanol, geraniol, guaiacol, 3-isobutyl-2-methoxypyrazine, 4-ethylguaiacol, acetoin and t-whiskylactone were at a concentration high enough to be odour-active. There were 30 compounds that were found to differ significantly between varieties. These include 3-isobutyl-2-methoxypyrazine, isoamyl acetate, isovaleric acid, ethyl isobutyrate, ethyl isovalerate, fusel alcohols, c-3-hexenol, methionol, eugenol, guaiacol and γ-nonalactone.

© 2000 Society of Chemical Industry

Quantitative determination of the odorants of young red wines from different grape varieties

The state of the art in aroma analysis is reviewed with emphasis on aroma-recombination studies using synthetic blends of odorants (aroma models) which have been prepared on the basis of analytical data. The model that matches the original aroma is the starting material for omission experiments which are performed to establish the odorants that actually contribute to the aroma. These experiments are discussed in detail for the aromas of two wine varieties, three olive oils of different provenance, French fries, boiled beef and coffee. The results indicate that odorants with higher odour activity values (OAV, the ratio of the concentration to the odour threshold) are frequently essential for the aroma. However, there are exceptions where odorants with high OAVs are suppressed in the aroma and compounds with lower OAVs are important contributors. These findings are discussed in the light of model experiments which have been reported in the literature to obtain an insight into the perceptual interactions of odorants in mixtures.

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Evaluation of the key odorants of foods by dilution experiments, aroma models and omission.

The aroma profile of five premium red wines has been studied by sensory descriptive analysis, quantitative gas chromatography−olfactometry (GC-O), and chemical quantitative analysis. The most relevant findings have been confirmed by sensory analysis. Forty-five odorants, including the most intense, were identified. At least 37 odorants can be found at concentrations above their odor threshold. A satisfactory agreement between GC-O and quantitative data was obtained in most cases. Isobutyl-2-methoxypyrazine, (E)-whiskey lactone, and guaiacol were responsible for the veggie, woody, and toasted characters of the wines, respectively. The sweet-caramel notes are related to the presence of at least five compounds with flowery and sweet notes. The phenolic character can be similarly related to the presence of 12 volatile phenols. The berry fruit note of these wines is related to the additive effect of nine fruity esters. Ethanol exerts a strong suppression effect on fruitiness, whereas norisoprenoids and dimethy...

Analytical characterization of the aroma of five premium red wines. Insights into the role of odor families and the concept of fruitiness of wines.

The value of, opportunities provided by, and the difficulties in elucidating the exact contribution that chemical compounds make to wine aroma and flavour are outlined and highlighted in this review. This paper provides an overview of the current understanding of relationships between wine sensory properties and volatile chemical composition through a discussion of recent studies where accurate, precise chemical data have been obtained for compounds shown by quantitative gas chromatography-olfactometry (GC/O) to be odour active in a sample. A centrepiece of this discussion is a compilation of compounds indicated to be most important to wine aroma. This is followed by a consideration of the limitation of odour activity values obtained by GC/O with particular reference to wine esters and volatile thiol compounds. The strengths of sensory descriptive analysis and its associated statistical methodologies to complement chemical composition data for aroma compounds are also explored. Grape flavour precursor compounds and the development of methods for their rapid quantification are then discussed in the context of the role of precursors contributing to wine aroma. Finally, an assessment is given of the likelihood in the near future of developing analytical strategies to measure wine flavour in relation to consumer expectations on the one hand, and on the other, to viticultural management practices to influence grape flavour composition.

Determining wine aroma from compositional data

Forty-four odor-active compounds were quantified in Scheurebe and Gewurztraminer wines, respectively. Calculation of odor activity values (OAVs) of odorants showed that differences in odor profiles...

H. Guth

Papers

Quantitation and Sensory Studies of Character Impact Odorants of Different White Wine Varieties