Sensorial Impact and Distribution of 3-Methyl-2,4-nonanedione in Cognacs and Spirits.

The aim of this study was to improve our knowledge on the chemical markers of Cognac aromas. We report results concerning the distribution and sensorial impact of 3-methyl-2,4-nonanedione (MND), a well-known compound in aged red wine, reminiscent of anise or "dried fruit", according to its concentration. We assayed first this diketone (solid-phase microextraction (SPME)-gas chromatography (GC)/mass spectrometry (MS), chemical ionization (CI)) in many Cognac samples followed by grappa, brandy, rum, whisky, vodka, and fruit spirits, and concentrations ranged from traces to 11.2 µg/L. Highest concentrations were obtained in grappa and freshly distilled eaux-de-vie of Cognac samples. Exceeding its detection threshold (100 ng/L, 70 vol %), MND contributes to the anise descriptor of these spirits. Its concentration decreased over aging while being highly correlated with the total amount of fatty acid ethyl ester. In addition, we showed that MND was produced during distillation according to the oxidation state of the white wine as well as the amount of lees used.

Contribution of Volatile Odorous Terpenoid Compounds to Aged Cognac Spirits Aroma in a Context of Multicomponent Odor Mixtures.

Cognac spirit aromas result from the presence of a wide variety of volatile odorous compounds associated with the modalities of spirit distillation and aging. However, very few studies have been carried out on aging notes of Cognac spirits. An HPLC fractionation approach was used in order to evidence fractions of interest recalling the specific aromatic nuances of aged Cognac. Then, a GC-O/MS analysis of the selected fractions allowed one to detect odorous zones and identify several volatile compounds. Among them, various well-known volatile compounds representative of the terpenoid family were highlighted, such as geraniol, α-terpinene, nerol, α-terpineol, 1,8-cineole (eucalyptol) and, particularly, piperitone, santalol, and α-campholenal, which have not previously been cited in Cognac. These compounds were quantitated and their detection thresholds were determined. Geraniol, α-terpinene, α-terpineol, and 1,8-cineole concentrations increased while spirits were more aged, while nerol tends to decrease. A sensory contribution of terpenes was observed through perceptual synergic effects, along with ß-damascenone and whisky lactone.

Quantitation, Organoleptic Contribution, and Potential Origin of Diethyl Acetals Formed from Various Aldehydes in Cognac.

Cognac wine distillate (WD), especially that produced during aging, is marked by complex and elegant aroma. This work aimed at expanding the knowledge on the Cognac WD aroma by a sensory-guided approach, involving a fractional-distillation technique and gas chromatography coupled to olfactometry and mass spectrometry (GC-O-MS). In doing so, a fruity-odor zone was highlighted in WD extracts that was attributed to the diethyl acetal family. Ten additional diethyl acetals were detected by GC-MS. Next, an assay method was developed and validated for seven of these diethyl acetals. Their detection thresholds were evaluated in a model solution of water/ethanol (60:40, v/v). 1,1-Diethoxy-3-methylbutane was shown to present a significant organoleptic impact because its olfactory-detection threshold (323 µg/L) is lower than its range of concentrations in WD (461 to 3337 µg/L). Given that diethyl acetals result from reactions between ethanol and aldehydes, quantitative correlations between diethyl acetals and corresponding aldehydes were considered.

Toward a Molecular Understanding of the Typicality of Chardonnay Wines: Identification of Powerful Aromatic Compounds Reminiscent of Hazelnut.

Chardonnay wines impart a unique complex aroma characterized by its buttery, yellow stone fruit, melon, bready, and woody notes. Among the terms used in the sensory analysis of these wines, this study investigated hazelnut-like attributes. Multidimensional gas chromatography coupled to olfactometry identified five pyrroles reminiscent of hazelnut: 1-ethylpyrrole-2-carboxaldehyde, 1H-pyrrole, 2-acetyl-1H-pyrrole (first identification in wine), 1-methylpyrrole-2-carboxaldehyde, and 1H-pyrrole-2-carboxaldehyde. Quantitative analyses demonstrated their significantly higher abundance in Chardonnay wines. However, they proved irrelevant in sensory terms, given the low amounts measured in wine compared to their olfactory detection threshold. Nevertheless, the presence of methanethiol derivatives from these pyrroles was investigated in wine. 1-Methylpyrrole-2-methanethiol and 1-ethylpyrrole-2-methanethiol were identified and exhibited hazelnut-like aroma. These compounds, which have not been observed in natural products to date, are potent volatile compounds with detection thresholds of 0.7 and 1.4 ng/L, respectively, in model wine. These findings open up promising perspectives concerning the interpretation of the typical aromatic nuances of some Chardonnay wines.