Using TDU-Pyrolysis-GC-MS to Investigate Aged Whiskey Samples and Their Oak Barrels

Importance of the topic

In whiskey production, aging in oak barrels drives complex chemical transformations that define color, aroma, and flavor. Non‐volatile compounds released from wood macromolecules accumulate in the spirit over time, impacting quality and authenticity assessment. Rapid profiling of solid residues after solvent removal can reveal links between barrel wood species and whiskey composition, offering tools for quality control and cask verification.

Study objectives and overview

This study applied temperature‐programmed pyrolysis combined with gas chromatography–mass spectrometry to:

• Compare non‐volatile residue profiles of 20‐year‐old whiskies matured in Quercus alba and Quercus robur barrels
• Analyze pyrolysis products from solid residues and corresponding oak wood samples
• Assess whether residue fingerprints can link whiskey to barrel wood species for maturation studies

Methodology

Whiskey samples (20 µL) were deposited into pyrolysis vials; volatile and semi‐volatile constituents were removed by two-stage thermal desorption at 300 °C. The remaining non‐volatile residue was pyrolyzed at 450 °C. Fractionated pyrolysis experiments determined optimal decomposition conditions. Comparative experiments were performed on both Quercus alba and Quercus robur whiskey residues and on wood chips from corresponding barrels.

Used instrumentation

This work utilized:

• GERSTEL Thermal Desorption Unit with pyrolysis module
• GERSTEL Cooled Injection System 4 with PTV inlet
• GERSTEL MultiPurpose Sampler autosampler
• Agilent 6890N GC coupled to 5795B inert mass selective detector
• MAESTRO software integrated with Agilent ChemStation for method control

Main results and discussion

Fractionated pyrolysis GC-MS generated distinct profiles for Quercus robur and Quercus alba whiskey residues. QR residue produced higher peak intensities (2–49×) and additional pyrolysis markers not present in QA. Twenty compounds, mainly lignin and cellulose degradation products (phenols, guaiacols, syringols, methoxyeugenol), were identified. Comparative analysis with oak wood pyrolysates confirmed that 17 of these markers originate directly from the barrel wood. Oak wood pyrolysis patterns validated the link between residue fingerprint and wood species.

Benefits and practical applications

Pyrolysis-GC-MS of whiskey solid residues offers:

• Rapid characterization of the non-volatile fraction with minimal sample preparation
• Discrimination between whiskies aged in different oak species
• Potential quality assessment metric for cask evaluation and authenticity verification
• Complementarity to existing volatile-component profiling methods

Future trends and potential applications

Extending this approach to time-series sampling (2–20 year maturation) could map the evolution of wood–spirit interactions. Integration with chemometric tools may enable predictive models for maturation level and wood origin. Adaptation to other aged spirits and exploration of pre-treatment effects (toasting, charring) will broaden applicability in spirits authentication and quality control.

Conclusion

TDU-Pyrolysis-GC-MS effectively profiles non-volatile whiskey residues, revealing species-specific markers that correlate to oak barrel type. The method is rapid, requires minimal sample handling, and can support maturity studies, cask selection, and authenticity verification in the spirits industry.

References

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4. Faix O et al. Thermal degradation products of wood. J Anal Appl Pyrolysis, 1990
5. Moldoveanu SC. Analytical Pyrolysis of Natural Organic Polymers. Elsevier