Analysis of Diacetyl and 2,3-pentanedione in Beer Using Nexis™ GC-2030

Importance of the Topic

The formation of vicinal diketones (VDKs), notably diacetyl and 2,3-pentanedione, during beer fermentation can lead to off-flavors described as butterscotch or buttery notes. Quantitative control of VDK levels is critical for flavor consistency and consumer satisfaction in brewing.

Objectives and Overview of the Study

This application note demonstrates a headspace gas chromatography method using the Nexis™ GC-2030 with HS-20 to quantify diacetyl and 2,3-pentanedione in beer. Two commercially available beer samples were analyzed before and after main fermentation to evaluate VDK concentration changes and the effectiveness of the diacetyl rest process.

Methodology and Instrumentation

Reagent Preparation and Calibration

• Standard solutions of diacetyl and 2,3-pentanedione at 25, 50 and 100 ppb (v/v) in water.
• Internal standard (2,3-hexadione) added at 50 ppb to all standards and samples.
• Calibration curves constructed from headspace analysis of standards in sealed vials.

Sample Preparation

• Non-degassed beer samples spiked with internal standard.
• 5 mL aliquots placed in headspace vials, heated at 60 °C for 90 min, then cooled.
• Headspace analysis performed to quantify both free and precursor-derived VDKs.

Instrument Configuration and Analytical Conditions

• Headspace Sampler: HS-20 in loop mode; vial heat 60 °C, pressurization 150 kPa, equilibration 40 min.
• GC System: Nexis™ GC-2030 with ECD-2010 Exceed detector.
• Column: SH-Rtx™-624 (60 m × 0.32 mm I.D., 1.8 μm film).
• Carrier gas: Helium at constant linear velocity (40 cm/s); split ratio 1:20.
• Oven program: hold at 50 °C, ramp 5 °C/min to 120 °C, hold 6 min.
• Detector: ECD at 130 °C, N₂ makeup gas at 15 mL/min, 2.5 nA current.

Main Results and Discussion

Calibration and Sensitivity

• Excellent linearity for diacetyl (R² = 0.9999) and 2,3-pentanedione (R² = 0.9978).

Quantitative Results in Commercial Beers

• Sample A: diacetyl 18.2 ppb, 2,3-pentanedione 1.8 ppb.
• Sample B: diacetyl 39.7 ppb, 2,3-pentanedione 7.1 ppb.

VDK Reduction During Diacetyl Rest

1. Day 4: diacetyl 208.9 ppb, 2,3-pentanedione 32.1 ppb.
2. Day 5: diacetyl 130.6 ppb, 2,3-pentanedione 18.6 ppb.
3. Day 6: diacetyl 101.7 ppb, 2,3-pentanedione 12.0 ppb.
4. Before bottling: diacetyl 39.7 ppb, 2,3-pentanedione 7.1 ppb.

This trend confirms effective yeast consumption of VDKs during the diacetyl rest and maturation processes.

Benefits and Practical Applications

• Rapid, sensitive quantitation of low-level VDKs without degassing or concentration steps.
• Reliable quality control tool for breweries to monitor fermentation and maturation.
• Enhanced process understanding enables optimized diacetyl rest and consistent flavor profiles.

Future Trends and Applications

Advancements in headspace GC and detector technology will further lower detection limits and analysis times. Integration with automated sampling systems and real-time monitoring could enable in-line control of fermentation processes. Expanding this approach to other aroma-impacting volatiles can broaden quality assurance in beverage production.

Conclusion

The Nexis™ GC-2030 with HS-20 headspace sampler offers a robust method for quantifying diacetyl and 2,3-pentanedione in beer. It delivers high sensitivity, linear response, and practical workflow for routine brewery quality control and research.

Reference

Narihiro Suzuki: Brewer Produces World’s Most Delicious Beer with Wild Yeast; Shinchosha (2019)