Analysis of Diacetyl and 2,3-Pentanedione in Beer Using Brevis GC-2050 (Carrier Gas: N2)

Importance of the Topic

Analyzing diacetyl and 2,3-pentanedione at trace levels in beer is critical for controlling off-flavor formation and ensuring consistent product quality. These vicinal diketones impart undesirable buttery notes when concentrations exceed sensory thresholds, affecting consumer acceptance and shelf life. Reliable quantification supports process optimization, including diacetyl rest and dry hopping management.

Objectives and Study Overview

This study evaluates a headspace gas chromatographic method using a Shimadzu HS-20 NX sampler coupled to a Brevis GC-2050 with an electron capture detector (ECD). Objectives include:

• Developing a calibration protocol for diacetyl and 2,3-pentanedione at ppb levels without pre-treatment
• Monitoring VDK concentrations before and after dry hopping and during secondary fermentation
• Applying the method to commercial beer samples to demonstrate real-world applicability

Methodology and Sample Preparation

Standard solutions of diacetyl and 2,3-pentanedione (10, 25, 50, 100 ppb) were prepared in water with 2,3-hexanedione as an internal standard (50 ppb). Beer samples (5 g) were mixed with the internal standard solution and heated at 60 °C for 90 minutes to promote headspace equilibration. Key headspace GC parameters:

• Loop mode at 40 °C, sample line at 90 °C, transfer line at 95 °C
• Vial pressurization: 150 kPa, heat retention 40 min
• Split injection ratio 1:20, injection time 0.5 min
• Nitrogen as carrier gas (constant linear velocity, 35 cm/s) and detector gas

Used Instrumentation

• Shimadzu HS-20 NX headspace sampler
• Shimadzu Brevis GC-2050 gas chromatograph
• Shimadzu ECD-2050 electron capture detector
• SH-624 capillary column (60 m × 0.32 mm, 1.80 µm)
• Nitrogen carrier gas supply

Main Results and Discussion

Calibration curves exhibited excellent linearity (R2 > 0.998) for both analytes. Chromatograms showed clear separation of diacetyl, 2,3-pentanedione, and internal standard peaks. Temporal analysis revealed an increase in VDK levels immediately after dry hopping, peaking on day three of secondary fermentation, followed by a decline by day 14, consistent with diacetyl rest. Commercial beers showed diacetyl concentrations between 46 and 233 ppb and 2,3-pentanedione levels of 10.8 to 19.9 ppb, indicating product-specific variability.

Benefits and Practical Applications

• Direct quantification at sub-ppb sensitivity without degassing or concentration steps
• Single gas (N2) for carrier and detector functions simplifies operation
• Compact instrument footprint ideal for brewery laboratories
• Robust method for quality control during fermentation, dry hopping, and maturation

Future Trends and Potential Applications

Future developments may include automated online sampling and integration with data analytics for real-time off-flavor monitoring. Expanding the method to additional volatile compounds or coupling with mass spectrometric detection could enhance flavor profiling. Compact, user-friendly systems will facilitate adoption in craft breweries and onsite quality control.

Conclusion

The Shimadzu HS-20 NX/Brevis GC-2050/ECD system delivers a sensitive, reliable, and space-efficient solution for trace-level analysis of diacetyl and 2,3-pentanedione in beer. Utilizing nitrogen and headspace sampling without extensive pretreatment, this method supports consistent flavor control and process optimization.

References

• Kishimoto T. The recent findings in the off-flavors of beer. Journal of Japan Association on Odor Environment, 44(1), 2013.
• Shimadzu. Analysis of Diacetyl and 2,3-Pentanedione in Beer Using Nexis GC-2030. Application News No. G316B.