Chemistry Composition the Aroma of Sauvignon Wine

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Table of Contents

Introduction
Chemical Components of Aroma
Methoxy-pyrazines
Other Components of Aroma
Fermentation of Sauvignon wine
Wine Aging
Aroma Analysis
Conclusion
Reference list

Introduction

Sauvignon is a dry white wine produced from a green-skinned grape, which is a variety that originates from Bordeaux, France. In addition, Sauvignon Blanc is planted in other wine-producing regions such as Chile, Australia, South Africa, California, and New Zealand whereby it is used to make a refreshing, crisp, and dry variety of white wine. However, the grape is also a major component of dessert wines such as those originating from Sauternes. The grape vines tend to grow vigorously, and thus, there is the need to prune and thin the shoots and leaves to increase fruit ripening. On the other hand, the varietal Sauvignon Blanc grape is similar to grapefruits, bell-peppers, grass or gooseberries depending on the region of origin (Marais, Hunter & Haasbroek, 1999, p. 19).

Characteristically, the level of pyrazine in the grape determines whether the varietal grape is intense or mild. Moreover, sufficient sunlight guarantees the production of melon-like aromas in the grape. Otherwise, insufficient lighting imparts an aggressive box tree odor to the grapes. Furthermore, depending on the climatic conditions under which the grape is cultivated, the flavor of Sauvignon Blanc wine can range from sweet to aggressively grassy.

When slightly chilled, Sauvignon wine can be served with fish, sushi, and cheese. Usually, Sauvignon wine is consumed young because aging does not have any significant contribution to its quality except for the oak-aged varieties from Bordeaux, which are known to age for approximately fifteen years (Marais et al., 1999, pp. 19-30). This essay presents a review of the components of aroma, the fermentation process, the aging process, and finally, aroma analysis about the Sauvignon Blanc wine.

Chemical Components of Aroma

Wine aroma contributes to the quality of wine in that the aroma components form an integral aspect of wine quality. Furthermore, the grape cultivar is a major contributor to wine quality because it determines the amount and type of the chemical components of aroma. As mentioned earlier, a typical varietal aroma of the Sauvignon grape can be identified as being vegetative, gooseberry, grassy, herbaceous, green pepper, or asparagus. However, these aromas can also be found in other varieties of grapes such as Semillon and Cabernet Sauvignon.

Accordingly, a review of the chemical components producing these aromas shows that the most important chemicals in Sauvignon Blanc are methoxy-pyrazines such as 2-methoxy-3-isobutylpyrazine (Marais, 1994, p. 42). Conversely, the grapes contain additional components such as 4-methyl-4-mercapto-pentane-2-one, C6-aldehydes, monoterpenes, C13-norisoprenoids, and C6-alcohols. These chemical components in Sauvignon Blanc are the major descriptors of the complex range of varietal aromas in white wines. Additionally, studies show that the level of methoxy-pyrazine, and thus, the varietal aroma of Sauvignon wine vary with climatic conditions, the plant origin, and the degree of ripeness.

Here, it is worth noting that the concentration of methoxy-pyrazine in Sauvignon Blanc decreases as the grape ripens, and also as the intensity of sunlight and temperature increases. Therefore, to produce varietal wines containing typical grape aromas, there is the need to cultivate the vines in cool areas and store the mature wines in dark places to retain the original aromas.

Methoxy-pyrazines

These are secondary products of the catabolism of amino acids, which are made up of a nitrogen-containing ring. As a result, the precursors of 2-methoxy-3-isopropylpyrazine include methionine, valine, and glycine. These compounds occur in beetroots, peas, potatoes, and green peppers. However, various quantitative techniques have been designed to study the low concentrations of methoxy-pyrazines in Sauvignon grapes.

According to Marais (1994, p. 43), Sauvignon Blanc grape contains 2-methoxy-3-isopropylpyrazine, 2-methoxy-3-sec-butylpyrazine, and 2-methoxy-3-isobutylpyrazine as shown in figure 1 below. These components contribute to the green pepper-like, pea-like, and asparagus-like aromas. Furthermore, the varietal aromas of Sauvignon Blanc wine rely on whether the concentration of each chemical component exceeds the threshold value.

Other Components of Aroma

The possibility that additional components do contribute to the varietal aromas of Sauvignon Blanc wines cannot be overlooked. Studies show that under acidic conditions, the extracts containing glycosidic precursors derived from Sauvignon Blanc do not have the grass-like, pea-like or the asparagus-like aroma, and thus, the pyrazine-derived aromas do not come from glycosides (Williams, Francis & Sefton, 1992).

Additionally, when hydrolysates released from their Sauvignon Blanc precursors through enzymatic reactions were added to neutral wines, the hydrolysates enhanced the aroma of the wine by imparting the floral, grassy, talc, pineapple, tea, toasty, oaky and the lime aromas. Probably, the floral and lime aromas were as a result of the monoterpenes; the honey-like and tea-like aromas were due to C₁₃-norisoprenoids; and finally, the oak-like aromas were caused by the phenolic components. Furthermore, additional studies show that the aromas caused by addition of enzyme-released hydrolysates to neutral wine can also be found in wines derived from Chardonnay and Semillon grapes (Sefton, Francis & Williams, 1994).

The monoterpenes containing a p-methene structure do occur in high concentrations in Sauvignon Blanc grapes as menthenediol-1, menthenediol-2, and trans- and cis-sobrerol in their bound forms (Versini et al., 1992). These chemical components, which are the oxidized forms of alpha-terpineol, increase in concentration as the wine ages. Moreover, the C₆-aldehydes and the C₆-alcohols contribute to the grassy, herbaceous-like, and leafy-like aromas of the Sauvignon wine (Singleton, 1998).

Fermentation of Sauvignon wine

As opposed to red wines, which are produced from the alcoholic fermentation of skins, musts, and the seeds, white wines are obtained from fermented grape juice. Therefore, fermentation of Sauvignon Blanc juice is preceded by juice extraction and juice clarification. Additionally, making of white wine may entail maceration, a process through which the solid components in the juice are solubilized. Moreover, it is worth noting that the taste of wine derived from any grape cultivar is determined by the pre-fermentation operations, which include harvesting, crushing, pressing, extraction, and clarification (Grainger & Tattersall, 2005, p. 64).

Therefore, the process of making white wine entails selective extraction of components of the grapes including the best portions of the grape and preventing the diffusion of some volatile components. As a result, successful white winemaking depends on the winemaker’s expertise in pressing the grapes and clarifying the juice or musts in such a way that achieves maximum extraction and preservation of the quality of grapes (Ribereau-Gayon et al., 2006, 398).

In recent years, the art of white winemaking has undergone several changes including the production of white wine in barrels instead of tanks. However, regardless of the fermentation method, the major fermentation operations in white winemaking include filling, yeast inoculation, addition of Ammonium salts and juice aeration, completion of alcoholic fermentation, and malolactic fermentation.

The first step in the fermentation of white wine entails filling, which is the process of adding clarified grape juice into fermentation tanks. This process leaves about 10% of the volume of the fermentation tank empty to avoid spilling of foam, which is produced in the subsequent phase of alcoholic fermentation. Moreover, this stage involves the assembly of different clarified juices in case a high-capacity tank is used (Ribereau-Gayon et al., 2000). Additionally, the fine lees that settle after racking the juice should be added into the juice before blending. Conversely, fresh juice should not be mixed with the fermenting juice because the fermenting yeasts can use the free SO₂ in the fresh juice to produce H₂S. Finally, immediately after constituting the blend, fermentation must be initiated.

The second fermentation operation in white winemaking involves yeast inoculation. This stage entails addition of a strong concentration of sulfates (usually at 10 g/hl) into juice to lower the effect of spoilage microflora and promote the activity of wine fermentors. Subsequently, the starter juice is allowed to undergo spontaneous fermentation before it can be inoculated into the newly filled tanks at a concentration of 2-5%. Here, it is important to note that the kinetics of fermentation relies on the indigenous strain of yeast present. Furthermore, clarification has been shown to disturb inoculation since slow fermentation may arise because of the low concentration of yeast.

On the other hand, selection of a suitable strain of yeast for fermentation is very important because there are more than 30 strains of Saccharomyces cerevisiae, which have the potential to produce white wine. Yeast selection entails an understanding of the fermentative potential of the strain and its overall effect relative to the specificity of the wine in question (Grainger & Tattersall, 2005, pp. 64-77).

The third stage of fermentation entails meeting the nitrogen and oxygen needs of the fermenting yeasts and constant aeration of the fermenting juice. Sometimes, assimilable nitrogen levels in juice derived from grapes cultivated in cool climates are sufficient to meet the nitrogen needs of the yeast. However, juices deficient in assimilable nitrogen can also be produced in cool climates especially when the vineyards are supplied with insufficient levels of nitrogen or due to increased summer dryness. As a result, juices with less than 160 mg of assimilable nitrogen require addition of ammonium sulfate during fermentation (Ribereau-Gayon et al., 2006, p. 426). Furthermore, there is the need to maintain temperature at constant levels since untimely changes in temperature can lead to thermal shocks, which can stop the fermentation process.

Conversely, completion of alcoholic fermentation in white winemaking depends on several factors such as the conditions, under which the juice is extracted, the concentration of sugars and assimilable nitrogen in the juice, the strain of yeast present, turbidity, the duration and frequency of aeration, and the fermentation temperature. However, these parameters can be controlled by the winemaker, which implies that a slow fermentation process is caused by carelessness on the part of the operator.

According to Ribereau-Gayon et al. (2000, p. 432), the duration of alcoholic fermentation in the production of white wine should not be more than 12 days. However, longer fermentation durations may arise when the juices contain high reducing sugar concentrations. In addition, the density of the fermenting juice should be monitored daily to assess the fermentation kinetics. Here, completion of alcoholic fermentation is achieved when the concentration of reducing sugars in the juice is less than 2g/l.

Wine Aging

Dry white wine is fermented and matured in barrels, which compensate for aroma deficient by imparting additional aromas derived from volatile substances in wood. These volatile substances in wood include phenols, octalactones, and phenol aldehydes. Traditionally, barrels derived from fine-grain oaks are used aging of dry white wine. The oaks are popular for their odorous components such as octalactones (Ribereau-Gayon et al., 2006, p. 438).

During barrel production, toasting influences the aromatic effect of the oak-wood on the wine. Here, the barrels should be toasted in such a way that the fragrant wood imparts a lower aromatic effect compared to the unstable wine aroma. Additionally, intermediate grain oak woods can also be used to produce medium toasted barrels, which are less fragrant, and thus, they cannot dominate the aroma of the white wine.

Wine aging commences immediately before completion of alcoholic fermentation. At this point, the barrels are filled with the juice to the top, and at the end of the fermentation process, the barrels are stirred daily until sulfating. On the other hand, barrel maturation of Sauvignon wine entails stirring and topping off of the juice on a weekly basis while maintaining the concentration of free SO₂ at 30 mg/l (Ribereau-Gayon et al., 2006, p. 439).

Aroma Analysis

The components of aroma consist of diverse classes of chemical compounds some of which are highly reactive or present in food at very low levels. As a result, the qualitative and quantitative analysis of aroma entails isolation of the volatile components, dilution analyses (differentiation of the aroma compounds from other compounds present in the volatile fraction), concentration and identification, quantification and calculation of the aroma value, simulation of the aroma relative to the analytical results, and finally, conducting omission experiments (Hans-Dieter, Grosch & Schieberle, 2009, p. 356).

During isolation, it is advisable to employ gentle methods, which eliminates the possibility of contamination. For instance, during fruit homogenization, hydrolases can enrich the fruit aroma with newly formed substances, and thus, there is the need to carry out the process in the presence of enzyme inhibitors. The most convenient methods of isolation include distillation, gas extraction, headspace analysis, enrichment, and the use of sensory relevance techniques (Hans-Dieter, Grosch & Schieberle, 2009, p. 360). Subsequently, the isolated compounds are then analyzed using various qualitative and quantitative methods such as Aroma Extract Dilution Analysis (AEDA), and Headspace GC Olfactometry.

On the other hand, to elucidate the structure of aroma substances, mass spectrometry should be the method of choice because of increased sensitivity. Further, enantioselective analytical procedures are employed to elucidate the absolute configuration and to calculate the enantiomeric ratio of aroma substances. Moreover, to determine the aroma values, quantitative methods such as Isotopic Dilution Analysis (IDA) are very beneficial. Finally, aroma models are designed in omission experiments to determine whether the odorants identified produce the actual aroma under study (Hans-Dieter, Grosch & Schieberle, 2009, p. 367).

Conclusion

This essay provides an extensive review of the production of Sauvignon wine with emphasis on the chemical components of aroma, the fermentation process, the process of wine aging, and aroma analysis. From the foregoing discussions, there are several descriptors for the varietal aromas of Sauvignon wine.

For instance, Sauvignon wine can be described as grassy, herbaceous, lime, tea, pea-like, asparagus-like or honey-like relative to the amount and variety of aroma substances derived from the grape cultivar. Here, we note that Sauvignon wine is a dry white wine that is derived from the white juice of Sauvignon Blanc grape, which is grown in several wine producing regions notably France and New Zealand.

On the other hand, there is no generally acceptable method of producing white wine, and thus, white winemaking can take place in a tank or barrel. Furthermore, it is worth noting that the recommended duration for the completion of alcoholic fermentation in white winemaking is approximately 12 days. Conversely, wine aging commences before alcoholic fermentation is complete, and this ensures that the fragile aroma of the white wine is maintained by imparting additional aromas derived from volatile substances in wood. Overall, the process of white winemaking is a tedious exercise, which relies on the expertise of the winemaker to determine the correct pre-fermentation operations, the fermentation operations, and the post-fermentation operations while maintaining the quality and aroma of the Sauvignon Blanc wine.

Reference list

Grainger, K. & Tattersall, H. (2005). Wine production: Vine to bottle. England: Wiley Blackwell.

Hans-Dieter, B., Grosch, W. & Schieberle, P. (2009). Food chemistry. New York: Springer.

Marais, J. (1994). Sauvignon blanc cultivar aroma – A review. Stellenbosch, SA: Nietvoorbij Institute for Viticulture and Oenology, Agricultural Research Council.

Marais, J., Hunter, J.J. & Haasbroek, P.D. (1999). Effect of season and region on Sauvignon Blanc grape composition and wine quality. South African Journal of Enology and Viticulture, 20, 19-30.

Ribereau-Gayon, P. Dubourdieu, D., Doneche, B. & Lonvaud, A. (2006). Handbook of enology: The microbiology of wine and vinifications, 2^nd ed. West Sussex, England: John Wiley & Sons Ltd.

Septon, M.A., Francis, I.L. & Williams, P.J. (1994). Free and bound volatile secondary metabolites of Vitis vinifera grape cv. Sauvignon blanc. J. Food Sci, 59, 142-147.

Singleton, V.L. (1998). Oxygen with phenols and related reactions in musts, wines, and model systems: Observations and practical implications. Am. J. Enol. Vitic., 44, 359-370.

Versini, G. Rapp, A. & Dalla Serra, A. (1992). Considerations about the presence of free and bound p-menth-1-enediols in grape products. Wurzburg, Germany: Proc. Int. Symp.

Williams, P.J., Francis, I.L. & Sefton, M.A. (1992). Sensory and chemical analysis of hydrolyzed flavor precursors from Sauvignon blanc grapes. Wurzburg, Germany: Proc. Int. Symp.

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