Spirits aged in wood or enriched with liquid wood extracts contain a wide diversity of phenolic compounds. These molecules play a key role in the structure, balance, and aromatic profile of the products… but they are also at the root of numerous analytical challenges.
Before addressing measurement methods, it is essential to understand where these compounds originate and how they evolve.
This article therefore provides:
an overview of the main phenolic compounds derived from wood that may be transferred to spirits;
a presentation of the major families of compounds and their key representatives — whether intrinsic to the wood, formed during toasting, or resulting from transformations occurring upon contact with alcohol or following the addition of liquid wood extracts;
a synthesis of the compounds with significant organoleptic impact, together with their main sensory characteristics;
an overview of the role of phenolic compounds in the evolution of spirits during wood ageing.
Finally, from an internal quality control perspective, the article reviews the main analytical methods available, outlining their advantages and limitations, and provides practical guidance for selecting the most appropriate method according to production objectives and budget constraints.
Description of the main wood-derived phenolic compounds that may be transferred to spirits – origin and organoleptic impact
Spirits aged in wood or enriched with liquid wood extracts contain a wide diversity of phenolic compounds. This chemical richness contributes to aromatic complexity and palate structure, but it also makes the interpretation of their sensory effects more challenging. Numerous scientific studies have addressed this topic; a non-exhaustive selection of references is provided at the end of the article, in the “Bibliography” section.
These compounds belong to several major families:
- les tanins ellagiques, responsables en grande partie de la structure et de l’astringence ;
- les acides phénoliques, souvent issus de la dégradation des tanins ;
- les aldéhydes phénoliques, parmi lesquels la vanilline, qui participent fortement au profil aromatique ;
- d’autres composés aromatiques extractibles, comme certains phénols issus du toastage ou des coumarines ;
- les sucres et polymères de sucres dégradés, à l’origine de composés aromatiques de type furfural ou maltol.
Figure 1 provides a simplified overview of the origin of these compounds, distinguishing :
compounds native to the wood;
products resulting from thermal degradation during wood toasting;
compounds formed or released during extraction into the alcoholic medium;
compounds resulting from oxidative transformations during ageing.
Figure 1
Note on the extractability of ellagitannins and the use of liquid wood extracts:
The nature of the extraction medium strongly influences the profile of transferred compounds, particularly the ethanol content and the presence of compounds liable to modify the polarity of the medium (ethyl acetate, acetaldehyde).
Aqueous wood extracts may favor the extraction of highly polar compounds, such as ellagitannins, which exhibit higher solubility in aqueous media than in concentrated hydroalcoholic solutions (5) (6).
Thus, the use of liquid wood extracts does not necessarily lead to the same molecular profile as that obtained during cask ageing.
Figure 2 illustrates the impact of the main compounds extracted from wood on the organoleptic properties of spirits aged in wood or enriched with liquid wood extracts.
Figure 2
Physicochemical roles of wood-derived phenolic compounds during the ageing of spirits
Reactivity with oxygen: Oak ellagitannins — notably castalagin and vescalagin — exhibit high reactivity toward dissolved oxygen and contribute to oxygen consumption during wood ageing. This property promotes oxidation and coupling reactions involved in the evolution of the spirit matrix. It may partly explain the acceleration of certain chemical transformations when oxygen input increases or when alternative wood products with a larger exchange surface area are used.
Influence on medium acidification: Certain phenolic compounds released from wood may contribute to a slight increase in the acidity of the medium, and thus to a decrease in pH. This acidification, in turn, promotes extraction phenomena and certain chemical reactions involved in the evolution of the spirit.
This aspect is discussed in more detail in the blog article “Consequences of Climate Change on the Quality and Stability of Spirits – Part 3”, particularly in the following sections:
Effects on the extraction of wood compounds
Effects on the composition of eaux-de-vie
Strengthening of water–ethanol interactions: Work conducted by Japanese researchers in 2005 suggests that the presence of phenolic compounds may strengthen hydrogen bonding between water and ethanol in distilled beverages (1).
Consequence: It is conceivable that phenolic compounds may not promote alcohol evaporation and could help limit the “angel’s share.”
The different analytical methods for wood-derived phenolic compounds in spirits
1. Global methods
To estimate the overall amount of phenolic compounds present in a spirit — or in a liquid wood extract — several approaches are based on light absorbance measurements:
– Measurement of UV absorbance at 280 nm
This method consists of measuring the intensity of light absorbed at 280 nm, after appropriate dilution of the sample to remain within the linear range of the spectrophotometer. It provides a global estimate of phenolic compounds absorbing in this region of the spectrum.
– Measurement of absorbance at multiple wavelengths (UV–Visible)
Absorbance is measured at different wavelengths in the UV and visible ranges, following dilution to ensure linearity of the spectrophotometric response.
The results are then processed using equations described in the literature or developed in-house, allowing the estimation of a tannin content, often expressed in mg/L or g/L of gallic acid equivalents (2).
– Chemical method known as the “Folin–Ciocalteu method”
Described in the OIV Compendium of International Methods of Analysis of Spirits (3), this method is based on a redox reaction: phenolic compounds reduce the Folin–Ciocalteu reagent, leading to the formation of a blue coloration measured by absorbance in the visible range, around 760 nm.
It provides a global estimate of the reducing capacity, largely attributed to polyphenols.
2. Selective methods
More selective approaches make it possible to target specific families of phenolic compounds or representative molecules.
They are based on separation techniques, mainly liquid chromatography (HPLC) or gas chromatography (GC), coupled with more or less specific detection systems (UV–Visible, fluorescence, mass spectrometry).
These methods allow the individual identification and quantification of key wood-derived compounds such as ellagic acid ,vanillin, W-lactones, eugenol,…
Comparison of analytical methods: advantages, limitations, and required resources
1- Direct methods based on light absorbance measurements
Advantages: These methods are simple to implement, rapid, and highly reproducible.
They are particularly useful for monitoring the “wood uptake” of an eau-de-vie during the addition of a liquid wood extract or throughout wood ageing.
Limitations: These measurements remain poorly selective and may lead to an overestimation of the phenolic compound content when other UV-absorbing substances are present in significant amounts.
Around 200–230 nm
This absorption region mainly corresponds to ellagitannins and phenolic acids. However, certain compounds resulting from the thermal degradation of wood sugars may also contribute to the absorbance, such as furfural.
Around 260–290 nm
This region includes the absorption of phenolic acids and simple polyphenols (gallic and ellagic acids). Aromatic aldehydes (for example, vanillin), as well as furfurylic compounds derived from caramelized sugars (such as 5-hydroxymethylfurfural), also absorb in this range.
Consequence : Heavy toasting of the wood or the possible addition of caramel to adjust color may cause interferences at certain wavelengths — particularly at 280 nm — leading to an overestimation of the phenolic compound content (2).
Equipment required:
a UV–Visible spectrophotometer;
cuvettes suitable for UV measurements;
basic laboratory glassware for dilutions (volumetric flasks, pipettes);
high-purity water (demineralized or reverse osmosis water, ideally filtered at 0.2 µm).
Financial requirements:
Investment budget: < €5,000
Operating costs: low (< €100 per year)
Required level of expertise:
Laboratory technician
2. Chemical methods and light absorbance measurement: the case of the so-called “Folin–Ciocalteu” method
Advantages
Unlike direct spectral measurements, which detect any compound absorbing in the UV range, the Folin–Ciocalteu method is based on a reaction that is more selective toward phenolic compounds:
- A more robust and standardized method (OIV);
- It is less sensitive to non-phenolic colored compounds responsible for interferences in the UV range (toasting products, caramel).
Limitations
This method provides a global estimate of the reducing capacity and not measure specific concentration in phenolic compounds:
- Other reducing compounds may also contribute to the signal;
- As a chemical method, it is sensitive to operating conditions (time, temperature, pH) and requires a higher level of technical control.
Equipment required:
a spectrophotometer covering the visible range up to at least 760 nm;
- cuvettes suitable for measurements in the visible range;
- basic laboratory glassware for dilutions (volumetric flasks, pipettes);
- a device enabling temperature control of the samples at 70 °C after addition of the reagent;
- the Folin–Ciocalteu reagent.
Financial requirements:
Investment budget: < €3,000
Operating costs: low (< €100 per year)
Required level of expertise:
Experienced laboratory technician
Note on the value of having a spectrophotometer:
A spectrophotometer covering at least the visible range is a versatile tool.
Beyond the analysis of phenolic compounds, it also makes it possible to monitor, compare, and adjust product color.
3- Chromatographic methods for the analysis of wood-derived phenolic compounds
Advantages
Chromatographic methods provide a more selective approach for characterizing wood-derived phenolic compounds.
Individual molecules of interest can be identified and quantified.
Examples of compounds that can be analyzed by chromatography:
- Determination of aromatic aldehydes (vanillin, syringaldehyde, sinapaldehyde, coniferaldehyde), furfurylic compounds (furfural, 5-hydroxymethylfurfural, and 5-methylfurfural), gallic and ellagic acids, vanillic and syringic acids, as well as scopoletin, whose influence on the organoleptic profile of spirits is well established (OIV method (4));
- Determination of ellagic acid before and after sample hydrolysis, providing an estimate of the ellagitannin content, the main family involved in tannic structure (EC Consulting in-house method).
Limitations
These methods remain targeted and do not, as such, allow for the direct estimation of the total phenolic compound content.
they require method development and validation adapted to each matrix (sample preparation, selection of the mobile phase, separation conditions);
relatively long analysis time compared with global methods;
sometimes complex interpretation of results in the presence of co-elutions or unidentified compounds.
These analytical techniques require substantial investment in chromatographic instrumentation (several tens of thousands of euros), an appropriate laboratory environment, highly qualified personnel, and high operating analytical costs.
When the number of analyses is relatively low, it may be preferable to outsource them to a qualified laboratory that will also be able to assist with the interpretation of the results.
Conclusion: How to choose the analytical method
In light of the elements presented in the previous sections, it appears that the choice of method depends on the type of control sought — monitoring “wood uptake,” assessing total polyphenol expression, or conducting an in-depth study of specific compounds — as well as on the level of selectivity required and the technical and budgetary resources available.
For internal quality control aimed at monitoring “wood uptake,” spectrophotometric methods based on absorbance at 280 nm or at multiple wavelengths offer a good compromise between simplicity, speed, and reproducibility.
When the risk of interferences is high — for example, due to a significant presence of compounds resulting from thermal treatment or the addition of caramel that may lead to an overestimation of absorbance — the chemical Folin–Ciocalteu method is preferable.
In a commercial or regulatory context requiring the expression of total polyphenol content, the Folin–Ciocalteu method remains the analytical reference.
To study the effect of ageing parameters such as wood type (tight grain/coarse grain), toasting level, or the impact of certain characteristics of the eau-de-vie — such as alcohol strength, aldehyde content, ethyl acetate content, etc. — at the time of casking, chromatographic analyses constitute a complementary tool. They allow the characterization and quantification of specific key compounds in order to interpret the associated organoleptic impact.
Two figures illustrate these conclusions:
Figure 3 presents, for each analytical method, the main compounds measured, the advantages and limitations, as well as a comparative estimate of investment and operating costs.
Figure 4 proposes, depending on the type of control sought, the most appropriate method or combination of methods.
Figure 3: Method – Compounds – Advantages and Limitations – Resources
Figure-4 : Objective – Recommended analytical method
With an internal quality control objective in mind, are you looking to equip your laboratory or optimize your analytical practices? In partnership with Dujardin-Salleron, I support you in defining and implementing solutions tailored to your project.
Evelyne CHANSON – Quality Control Wines and Spirits Consultant at EC Consulting
I would like to thank BIOSSENT , specialist in oak and vigne extracts, for its contribution to the preparation of this article.
If you enjoyed this article, or if it raises a need for further information or corrections, please feel free to let me know
by email at: evelyne.chanson@gmail.com or in the comment section at the bottom of this article.
References cited in this article
(1) 2005 – « Hydrogen Bonding in Alcoholic Beverages (Distilled Spirits) and Water-Ethanol Mixtures” – A. NOSE, T. HAMASAKI, M. HOJO, R. KATO, K. UEHARA, T. UEDA – J. Agric. Food Chem., 2005, 53, 7074-7081.
(2) « Dosage rapide dans les Cognacs des composés phénoliques totaux par spectroscopie U.V. » – ,J. LAVERGNE, J.M. OLIVIER, C. RAFFIER –
(3) « Détermination globale des composes phénoliques dans les boissons spiritueuses d’origine vitivinicole sans addition de caramel » – Méthode OIV-MA-BS-19.
(4) « Dosage des principaux composés extraits du bois lors du Vieillissement – Dosage du furfural, du 5-hydroxyméthylfurfural et du 5-méthylfurfural, de la vanilline, de la syringaldéhyde, de la coniféraldéhyde et de la sinapaldéhyde, des acides gallique et ellagique, des acides vanillique, syringique et de la scopolétine par chromatographie en phase liquide à haute performance”. Méthode OIV-MA-BS-16
(5) 2015 – “Understanding the ellagitannin extraction process from oak wood” – García-Estévez I. et al. – Tetrahedron, 71, 3089–3094. https://doi.org/10.1016/j.tet.2014.10.047
(6) 2013 – “Impact of ethanol content on the scavenging activities of oak wood C-glycosidic ellagitannins – Application to the evaluation of the nutritional status of spirits » – Vivas N., Vivas de Gaulejac N., Vitry C., Mouche C., Kahn N., Nonier-Bourden M.-F., Absalon C. – J. Inst. Brewing, 119(3), 116–125 – https://doi.org/10.1002/jib.70
Additional references
About the composition of oak wood and its organoleptic contribution
1987 – « Composition Chimique des Bois de Chêne : composés phénoliques, relation avec quelques propriétés physiques et chimiques susceptibles d’influencer la qualité des eaux-de-vie » – B. MONTIES – Connaissance Vigne Vin, 1987, 21, N°3, 169-190.
1990 – “Volatile norisoprenoid compounds as constituents of oak woods used in wine and spirit maturation” – SEFTON M.A., FRANCIS I.L., WILLIAMS P.J. – J. Agric. Food Chem , 1990 , 38 , 11 , 2045-2049.
1993 – “The influence of natural seasoning on the concentrations of eugénol, vanillin, and cis- and trans-b-methyl-j-octalactone extracted from french and american oakwood” – SEFTON M.A., FRANCIS I.L., POCOCK K.F., WILLIAMS P.J. – Sci. Aliments , 1993 , 13 , 629-643.
1995 – « Influence des procédés de tonnellerie et des conditions d’élevage sur la composition et la qualité des vins élevés en fûts de chêne » – Pascal CHATONNET – Thèse de doctorat – Sciences biologiques et médicales, Œnologie-ampélologie.
1996 – « Composition Chimique du Bois de Chêne de Tonnellerie » – G. MASSON, J.L. PUECH, M. MOUTOUNET – Bulletin de l’O.I.V., 1996, 785-786.
2005 – « Comparison of volatile composition of cooperage oak wood of different origins (Quercus pyrecaica vs., Quercus Alba and Querpetra)” A. M. Jordao, J. M. Ricardo-Da-Siva, O. Laureano, Mitteilungen Klosterneuburg, 2005, 55, 22-31.
2006 – « Influence of Geographical Origin and Botanical Species on the Content of Extractives in American, French, and East European Oak Woods” – ANDREI PRID, JEAN-LOUIS PUECH – J. Agric. Food Chem. 2006, 54, 8115-8126.
About the seasoning of staves
1993 – « Les phénomènes liés à la maturation du bois de chêne pendant son séchage » – VIVAS Nicolas – Revue des œnologues, 70 , 17-21.
About the impact of toasting on the formation of aromatic compounds
1993 – « The effect of cask charring on scotch whisky » – CLYNE J., CONNER J.M., PATERSON A., PIGGOTT J.R. – International Journal of Food Science and Technology, 1993, 28, 69-81.
1997 – « Identification of Volatile Compounds with a “Toasty” Aroma in Heated Oak Used in Barrelmaking » – Isabelle CUTZACH, Pascal CHATONNET, Robert HENRY, Denis DUBOURDIEU – J. Agric. Food Chem, 1997, 45, 2217 – 2224.
1999 – « Monitoring Toasting Intensity of Barrels by Chromatographic Analysis of Volatile Compounds from Toasted Oak Wood » – Pascal CHATONNET, Isabelle CUTZACH, Monique PONS, Denis DUBOURDIEU – J. Agric. Food Chem, 1999, 47, 4310-47318.
2003 – « Incidence du niveau de chauffe du bois sur une eau-de-vie de cognac logée en fût neuf : Étude pilote » – G. SNAKKERS, J.-M. BOULESTEIX, Sylvie ESTRÉGUIL, Jacqueline GASCHET, Odile LABLANQUIE, Annie FAURE et R. CANTAGREL, J. Int. Sci. Vigne Vin, 2003, 37, n°4, 243-255.
About the ageing of eaux-de-vie
1972 – « Contribution à l’étude du vieillissement du cognac. Identification de la scopolétine, de l’aesculétine, de l’ombelliférone, de la B-methyl-ombelliférone, de l’aesculine, et de la scopoline, hétérosides provenant du bois » – JOSEPH E., MARCHE M. – Conn. Vigne et Vin , 1972 , 6 , 273-330.
1990 – « Relationships between phenolic compounds of low molecular weight as indicators of aging conditions and quality of brandies » – DELGADO T., GOMEZ-CORDOVES C., VILLARROYA B. – Am. J. Enol. Vitic., 1990, 41, 4, 342-345.
1993 – « Ellagitannins and lignins in aging of spirits in oak » – Carole VIRIOT, Augustin SCALBERT, Catherine LAPIERRE, Michel MOUTOUNET- J. Agric. Food Chem, 1993, 41, 1872 – 1879.
2017 – « Phenolic Composition and Related Properties of Ages Wine Spirits: Influence of Barrel Characteristics, A review » – Sara CANAS – Beverages 2017, 3, 55.
1987 – « Etude par chromatographie en phase gazeuse de substances volatiles issues du bois de chêne » – MARSAL F., SARRE Ch. – Conn. Vigne et Vin , 1987 , 21 , 1 , 71-80.
1987 – “Phenolic compounds from the heartwood of European oak (quercus robur L.) and brandy” – NABETA K., YONEKUBO J., MIYAKE M. – Mokuzai Gakkaishi , 1987 , 33 , 5 , 408-415.
1988 – “Evolution of the Italian Distillate Grappa during Aging in Wood: A Gas Chromatographic and High Performance liquid Chromatographic Study” – PROFUMO A., RIOLO C., PESAVENTO M., FRANCOLI A. – Am. J. Enol. Vitic. , 1988 , 39 , 4 , 273-278.
1996 – « Etude expérimentale de l’évaluation de l’impact organoleptique du bois de chêne sur le Cognac » -Rapport du BNIC , 1996 , 221-233.
2016 – “Oxygen consumption by oak chips in a model wine solution; Influence of the botanical origin, toast level and ellagitannin content” – Navarro et al. – Food Chem., 2016, Vol. 199, 1-910.
2017 – « An Approach to the Study of the Interactions between Ellagitannins and Oxygen during Oak Wood Aging”- García-Estévez et al., – J. Agric. Food Chem., 2017, May 23.
2017 – « Oxygen consumption rates by different oenological tannins in a model wine solution », Pascual et al. – Food Chem., 2017, Vol. 234, 26-32.
2021- « Structures chimiques et évolution de la composition en ellagitanins dans les bois et spiritueux : étude sur les eaux-de-vie de Cognac » – Mathilde GADRAT – Thèse de l’Université de Bordeaux – https://theses.hal.science/tel-03917127v1/file/GADRAT_MATHILDE_2021.pdf
2022 –“Phenolic Composition and Related Properties of Aged. Wine Spirits: Influence of Barrel Characteristics – A Review” – CANAS S. – Beverages 2017, 3(4), 55.
2025 – « Les méthyl-cétones et le rancio charentais » – FLASH-INFO – laboratoire EXCELL – https://labexcell.com/images/FlashInfo/FI_FR_Methyl-cetones.pdf
Comparison with alternative systems to barrel ageing
2009 – “Comparison of alternative systems for the ageing of wine brandy, wood shape and wood botanical species effect” – CANAS S., CALDEIRA I., BELCHIOR A.P. ,Ciência Téc. Vitiv. v.24 n.2 Dois Portos 2009 , 24 , 2 , 33-40.
2013 – “Comparative study of two aging systems for cider brandy making. Changes in chemical composition” – MADRERA R.R., HEVIA A.G., VALLES B.S. ,Food Science and Technology 54 , 2013 , 54 , 513-520.
2013- “Variation of Extractable Compounds and Lignin. Contents in Wood Fragments Used in the Aging of Wine Brandies” – Ofélia Anjos, Clarisse Carmona, da Caldeira,c, Sara Canas – BioResources 8(3), 4484-4496 –
https://bioresources.cnr.ncsu.edu/BioRes_08/BioRes_08_3_4484_Anjos_CCC_Variation_Extractable_Lignin_Wood_Aging_Brandies_4229.pdf
2023 – “The Impact of Compounds Extracted from Wood on the Quality of Alcoholic Beverages” – Tomasz Tarko, Filip Krankowski, Aleksandra Duda-Chodak – Molecules, 2023, 7, 28(2), 620 – https://www.mdpi.com/1420-3049/28/2/620
2025 – “Role of ellagitannins and OTR of the Quercus petraea (Matt.) Liebl barrel staves for beverages aging » – Álamo-Sanza et al. – Food Chem., 2025, Vol. 32, 1032852025.
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