1/ Impact of barrel toasting on eaux-de-vie perception

After a long training course, the judges came to a consensus regarding the descriptors to be used for studying the impact of barrel toasting (temperature and duration) on eaux-de-vie at 40 % (v/v) (as they are marketed at 40 % (v/v)). The seven chosen descriptors were: “leather”, “freshness”, “tobacco”, “toasted”, “dry wood”, “sweetness” and “heat”. In general, of the two factors toasting and duration, toasting temperature had a greater impact than duration. For toasting duration, only one descriptor was significantly affected by duration: “freshness”. A normal toasting (N) of the barrel produced a more intense freshness than a slower toasting (S). Out of the seven consensus descriptors, five were significantly impacted by the toasting temperature of the barrel only: “dry wood”, “leather”, “tobacco”, “toasted” and “sweetness” (Figure 1). This was therefore the main factor that discriminated and characterised the different eaux-de-vie. The eaux-de-vie aged in highly toasted barrels were significantly more intense in terms of “dry wood”, “leather”, “tobacco” and “toasted” notes compared to the eaux-de-vie in lightly toasted barrels. They were also significantly more intense in “dry wood” and “tobacco” notes than the eaux-de-vie in medium and medium+ toasted barrels. However, an eau-de-vie aged in a lightly toasted barrel was characterised by a higher “sweetness” intensity than the eaux-de-vie aged in medium plus and highly toasted barrels.

Figure 1. Descriptor intensity in eaux-de-vie at 40 % (v/v) with different barrel toasting temperatures (LT: Light toast, MT: Medium toast, MT+: Medium toast +, and HT: High toast). Error bar represents the confidence interval with a threshold of 0.05 (adaped from Gadrat et al. 2022)⁶.

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Under the conditions of this experiment, the “heat” notes were perceived as being the most intense in eaux-de-vie from highly toasted barrels, suggesting that the sensation of heating may influence the perception of sweetness. Studies have shown that high alcohol levels contribute to the sensation of “heating” or “hotness”⁷ and alter the perception of sweetness⁸. It is therefore possible that the lower perception of sweetness in the eaux-de-vie from highly toasted barrels was linked to the intense “heat” sensation of the spirit.

The effect of toasting temperature was so important that clustering permitted to classify the eaux-de-vie into groups according to their sensorial proximity. Figure 2 shows that three groups of eaux-de-vie were formed. The first group contained the eaux-de-vie aged in highly toasted barrels and in a MT+S barrel. The second group consisted of eaux-de-vie aged in barrels with two medium toasts, MTN and MT+N. Finally, the third group was made up of eaux-de-vie aged in lightly toasted barrels and in MTS barrels. As there are no previous studies on the impact of toasting on cognac eaux-de-vie from a sensory point of view, these results cannot be compared with other studies.

Figure 2. Clustering of eaux-de-vie based on the consensus descriptors for the eight products (adapted from Gadrat et al. 2022)⁹.

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2/ Evaluation of eaux-de-vie quality

After the sensory profile, the eaux-de-vie were classified according to their olfactory and gustatory characterisation and to their overall quality using a ranking test. Each taster was asked to assign 1 point to the lowest-quality eau-de-vie and 8 points to the highest. The sum of the ranks was calculated for each modality for each ranking. As can be seen in Table 2, the highest sum of ranks in the olfactory and the overall quality ranking was observed for the eaux-de-vie aged with HTS and HTN barrels, followed by MT+S, LTS, MT+N barrels, and MTS, MTN and LTN barrels. The only difference was the significance level of differentiation among the samples: in olfactory ranking the level is higher (see letters showing the differences in Table 2). The gustatory ranking also shows a significant difference of 0.5 % among the products (Table 2), but the ranking differs. Unlike the results of the olfactory and overall quality ranking, the two high toasts showed a very different rank sum and did not differ from the light toast LTS. The eau-de-vie aged in the HTN barrel had the highest rank sum, but did not differ from the eaux-de-vie corresponding to the HTS, MT+S, LTS, MT+N and MTS barrels.

Table 2. Ranking of perceived quality in eaux-de-vie after 12 months of ageing in barrels representing different toasts (adapted from Gadrat et al. 2022)¹⁰.

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Figure 3 shows the results of the overall quality ranking test for the 40 % (v/v) eaux-de-vie according to toasting duration (Normal or Slow) for each barrel toasting temperature. When the duration is ‘slow’ the light toast results in higher quality than the medium toast, but to a lesser extent than the MT+ and HT toasts. On the other hand, when the toasting is ‘normal’ it is possible to differentiate the eaux-de-vie according to the toasting temperature, with high toasting temperatures resulting in a more qualitative eaux-de-vie than light toasting temperatures.

Figure 3. Results of the overall ranking of the 40 % (v/v) eaux-de-vie according to toasting duration (Normal or Slow) for each barrel toasting temperature (LT, MT, MT+ and HT) (adapted from Gadrat et al. 2022)¹¹.

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Notes

• Canas, S. (2017). Phenolic Composition and Related Properties of Aged Wine Spirits : Influence of Barrel Characteristics. A Review. Beverages, 3(4), 55. https://doi.org/10.3390/beverages3040055
• Canas, S., Belchior, A. P., Falcão, A., Gonçalves, J. A., Spranger, M. I., & Bruno-de-Sousa, R. (2007). Effect of heat treatment on the thermal and chemical modifications of Oak and Chestnut wood used in brandy ageing. Ciência e Técnica Vitivinícola, 22(1), 5 14.
• Cadahía, E., Muñoz, L., Fernández de Simón, B., & García-Vallejo, M. C. (2001). Changes in Low Molecular Weight Phenolic Compounds in Spanish, French, and American Oak Woods during Natural Seasoning and Toasting. Journal of Agricultural and Food Chemistry, 49(4), 1790 1798. https://doi.org/10.1021/jf0006168
• Chira, K., Anguellu, L., Da Costa, G., Richard, T., Pedrot, E., Jourdes, M., & Teissedre, P.-L. (2020). New C-Glycosidic Ellagitannins Formed upon Oak Wood Toasting, Identification and Sensory Evaluation. Foods, 9(10). https://doi.org/10.3390/foods9101477
• Gadrat, M., Lavergne, J., Emo, C., Teissedre, P. L., & Chira, K. (2022). Sensory characterisation of Cognac eaux-de-vie aged in barrels subjected to different toasting processes. OENO One, 56(1), 17–28. https://doi.org/10.20870/oeno-one.2022.56.1.4853
• Gadrat, M., Lavergne, J., Emo, C., Teissedre, P. L., & Chira, K. (2022). Sensory characterisation of Cognac eaux-de-vie aged in barrels subjected to different toasting processes. OENO One, 56(1), 17–28. https://doi.org/10.20870/oeno-one.2022.56.1.4853
• Gawel, R., Sluyter, S. V., & Waters, E. J. (2007). The effects of ethanol and glycerol on the body and other sensory characteristics of Riesling wines. Australian Journal of Grape and Wine Research, 13(1), 38 45. https://doi.org/10.1111/j.1755-0238.2007.tb00070.x
• Zamora, M. C., Goldner, M. C., & Galmarini, M. V. (2006). Sourness–Sweetness Interactions in Different Media : White Wine, Ethanol and Water*. Journal of Sensory Studies, 21(6), 601 611. https://doi.org/10.1111/j.1745-459X.2006.00085.x
• Gadrat, M., Lavergne, J., Emo, C., Teissedre, P. L., & Chira, K. (2022). Sensory characterisation of Cognac eaux-de-vie aged in barrels subjected to different toasting processes. OENO One, 56(1), 17–28. https://doi.org/10.20870/oeno-one.2022.56.1.4853
• Gadrat, M., Lavergne, J., Emo, C., Teissedre, P. L., & Chira, K. (2022). Sensory characterisation of Cognac eaux-de-vie aged in barrels subjected to different toasting processes. OENO One, 56(1), 17–28. https://doi.org/10.20870/oeno-one.2022.56.1.4853
• Gadrat, M., Lavergne, J., Emo, C., Teissedre, P. L., & Chira, K. (2022). Sensory characterisation of Cognac eaux-de-vie aged in barrels subjected to different toasting processes. OENO One, 56(1), 17–28. https://doi.org/10.20870/oeno-one.2022.56.1.4853