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Chapter 11
Correlation between the Concentrations of Two Oak Derived Key Odorants and the Intensity of a Woody-“Barrique-Type” Odor Note in Different Red Wines Stephanie Frank and Peter Schieberle* German Research Center for Food Chemistry, Lise-Meitner-Strasse 34, D-85354 Freising, Germany *Telephone: +49 8161 71 2932. Fax: +49 8161 71 2970. E-mail:
[email protected].
During barrel aging, in particular, odorants like cis- and trans-whiskylactone, vanillin and several phenols are released into the wine. However, although in aroma profile analyses odor qualities like woody, vanilla or coconut-like are often used to describe the “barrique-type” aroma, a clear correlation between the intensity of such aroma qualities in the overall profile and the concentrations of key odorants, often displaying similar odor qualities, is scarcely available. On the basis of a comparison of the key odorants in a Dornfelder red wine aged in barrels or steel tanks, respectively, this study attempted to correlate, in particular, the intensity of the “barrique” aroma in some commercial red wines with the concentrations of cis-whiskylactone and vanillin.
The aroma is an important quality attribute of wine, and thus, the identification of volatile compounds in either white or red wine has been a research topic of numerous investigations in the past. So far ~400 volatiles have been identified (1). It is well-accepted in the literature that, besides the grape variety, the process of wine manufacturing and storage has a clear influence on the overall aroma of the final product, and in particular, red wines stored in oak barrels (barrique-type) are often rated by the consumer to be of higher quality. The term “barrique” is French © 2011 American Chemical Society Ebeler et al.; Progress in Authentication of Food and Wine ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
and means small wine barrel, which, by definition, is a wooden barrel with a small volume, typically 225 liters (2). The most frequently applied wood in cooperage is oak imparting the typical sweet-woody or barrique-type aroma to wines stored in oak barrels (3, 4). Several compounds have been suggested to contribute to the typical aroma of barrel aged wine, and cis-whiskylactone and vanillin are among the most addressed volatiles (5, 6). Concepts of molecular sensory science, such as GC-olfactometry, the calculation of odor activity values and, finally, aroma recombination experiments have been proven as useful tools to characterize the key aroma compounds of foods (7). The application of such concepts on, e.g., white wine (8), Bourbon whisky (9) or tea (10) have recently shown that only a limited number of several key odorants are able to interact with the odorant receptors in the human olfactory organ during food perception, thus creating the final aroma in the brain. On the basis of such results, it has, however, turned out that, although often only about 20-30 key odorants are able to mimick the typical aroma of the respective food, usually none of them elicits an odor close to the odor of the food itself. As previously shown by sensory experiments, the human olfactory system is not able to detect the presence of a single constituent on the basis of its odor quality in mixtures containing more than three odorants (11). The fact that single odorants cannot be identified in a mixture seems to be a limitation of human aroma perception, however, obviously the sense of smell provides a means to identify quite complex mixtures of aroma compounds within seconds on the basis of a certain aroma profile. Thus, because sensory panels are able to describe the intensities of single aroma qualities when evaluating food aromas, it is a challenge in flavor science to correlate the odor qualities detected by a sensory panel with the presence or the concentrations, respectively, of single key odorants. Using the concept of molecular sensory science (7), in a recent study, the key odorants present in a Dornfelder red wine manufactured as barrique-style were identified and compared to those present in a red wine from the same batch, but stored in a steel tank (12). In particular cis-whiskylactone and vanillin, but also four aroma-active phenols showed higher concentrations in the barrel aged wine (12). However, although these aroma compounds have been identified as volatile constituents in red wines several times before (5, 6), their contribution to the overall aroma of red wines manufactured by the “barrique” method is still not clear. Thus, the aim of the present study was to elucidate whether a correlation between an overall “sweet-woody” odor note in barrel aged red wines and, in particular, cis-whiskylactone and vanillin does exist.
Experimental Part Wines Five commercial barrel aged red wines of different origin and varietal were purchased from a local wine store: A Pinot Noir from Germany (vintage 2007), a Cabernet Sauvignon from Chile (vintage 2007), a Bordeaux from France (vintage 2004), a Rioja from Spain (vintage 2003) and a Barolo from Italy (vintage 2001). 166 Ebeler et al.; Progress in Authentication of Food and Wine ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
In addition, a Dornfelder red wine was obtained from a winegrower in Saulheim (Rheinhessen), Germany. This wine (vintage 2008) had either been stored in oak barrels or had been stored in steel vessels, respectively. Aroma Profile Analysis Aroma profile analyses were performed by a trained sensory panel consisting of 14 panelists as previously described (12). The following aroma descriptors, represented by the compound given in parentheses, were chosen for sensory evaluation, and their intensities were ranked on a seven-point scale (steps of 0.5) from 0 (not perceivable) to 3 (strongly perceivable): flowery (2-phenylethanol), malty (3-methyl-1-butanol), fruity (ethyl 3-methylbutanoate), cooked apple-like ((2E)-1-(2,6,6-trimethyl-cydclohex-1-en-1-yl)but-2-en-1-one), clove-like (4-allyl-2-methoxyphenol), sweaty (3-methylbutanoic acid), smoky (2-methoxyphenol), vanilla-like (4-hydroxy-3-methoxy-benzaldehyde), coconutlike ((4S,5S)-5-butyl-4-methyldihydrofuran-2(5H)-one; cis-whiskylactone), vinegar-like (acetic acid), butter-like (2,3-butandione), and cooked potato-like (3-(methylthio)-propanal). The judgments of the panelists were averaged. Simulation of the Barrique-Type Aroma Note in the Dornfelder Red Wine A Dornfelder red wine, which had been stored in steel vessels, was spiked with five odorants: cis-whiskylactone, vanillin, 4-ethyl-2-methoxyphenol, 2-methoxyphenol and 4-ethylphenol. The amounts of the five odorants added were chosen in the way that the concentrations in the resulting wine were the same as in a wine of the same batch, which had been stored in oak barrels. The overall similarity of the aroma was ranked as described recently (12). Sensory Evaluation of the Barrique-Type Aroma Note in Commercial Red Wines The intensity of the barrique-type odor quality in five commercial red wines was ranked by a trained sensory panel consisting of 18 panelists. The panel ranked the intensity of this note in the wines using an eleven step scale from 1 to 5. As a reference, the odor descriptor for the barrique aroma was defined as “sweetwoody”, and was represented by a model solution of cis-whiskylactone (2.2 mg/L) and vanillin (15.9 mg/L) in ethanol/water (13%). Quantification by Stable Isotope Dilution Assays (SIDA) Wine (0.5 mL - 400 mL), depending on the amount of the respective odorant present, was spiked with isotopically labeled vanillin and cis-whiskylactone, respectively, and after equilibration, extracted with diethyl ether. After drying over Na2SO4, the volatiles and the internal standards were isolated by SAFE distillation, and the analytes were quantified by mass chromatography as recently reported (12). 167 Ebeler et al.; Progress in Authentication of Food and Wine ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
Sensory Study on the Correlation of the Concentrations of Vanillin and cis-Whiskylactone with the Intensity of a “Sweet-Woody” Note Solutions of either vanillin or cis-whiskylactone, respectively, dissolved in 13% ethanol in water, were presented to the sensory panel in increasing concentrations. In triangle test, either one or two samples contained the double concentrations of the reference, and the panel had to identify the vessel containing the higher concentration. The evaluation of the results was done according to § 64 LFGB method BVL L 00.90-7 appendix A.1 (13).
Results In a first sensory experiment, the aroma profiles of the barrel aged Dornfelder red wine and of the same wine aged in a steel tank were determined. The data showed that, in particular, the vanilla-like and the smoky-sweet but also the coconut-like aroma notes were higher in the barrel aged wine (Table I). Quantitation of the most odor-active compounds in both wines revealed no significant changes for most odorants, but, in particular, cis-whiskylactone, vanillin and three phenols were much higher in the barrel aged wine (12).
Table I. Comparison of the aroma profile analysis of the Dornfelder red wine aged in an oak barrel (OB) or a steel tank (ST) Intensity Odor quality
OB
ST
Fruity
2.0
2.0
Flowery
1.6
1.6
Malty
1.5
1.1
Cooked apple
1.8
1.1
Vanilla-like
1.7
0.4
Smoky-sweet
2.3
1.0
Clove-like
2.1
1.0
Coconut-like
1.0
0.4
Sweaty
0.7
1.3
One option to test the contribution of oak derived odorants to the overall “barrique-type” aroma of a wine is spiking wine from the same batch, which has been stored in steel barrels, with reference compounds matching their natural concentrations in wine of the same batch, which had been stored in oak barrels. This experiment was performed using the quantitative data for two Dornfelder red wines of the some batch either stored in steel tanks or in oak barrels, respectively (Table II). 168 Ebeler et al.; Progress in Authentication of Food and Wine ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
Table II. Concentrations of five selected odorants in Dornfelder red wine differing in their concentrations after aging in steel tanks (ST) or oak barrels (OB), respectivelya Odorant
a
Conc. (µg/L) ST
OB
cis-whiskylactone
