FASTER GAS CHROMATOGRAPHY AND ITS UTILIZATION IN BREWING. PART 3. – THE DETERMINATION OF SOME LOW VOLATILE BEER FLAVOURS

Importance of the Topic

Gas chromatography is a cornerstone technique for profiling flavor-active compounds in beer, such as fatty acids and higher alcohols. Accelerating GC analyses without loss of resolution increases laboratory throughput, reduces costs, and supports rapid quality control in brewing.

Objectives and Study Overview

This study evaluates narrow-bore capillary columns (10 m × 0.18 mm i.d.) with DB-WAX stationary phase for quantifying low-volatile beer flavor compounds. Results are compared to conventional 30 m × 0.32 mm columns to assess speed gains, reproducibility, and method robustness for:

• Free short-chain fatty acids (C4–C10)
• Higher fatty acids (C12–C18) as methyl esters
• Selected higher and aromatic alcohols

Methodology and Instrumentation

Sample preparation involved solid-phase extraction or steam distillation with liquid–liquid extraction. Fatty acids were analyzed as free acids or converted to methyl esters using BF₃-methanol. Higher alcohols were directly extracted.
All analyses used an Agilent-type GC system equipped with split/splitless injector, flame ionization detector (FID), and autosampler. Carrier gas: helium. Chromatographic parameters (oven ramps, flow rates, split ratios) were translated from the 0.32 mm column to the 0.18 mm column using method translation software.

Main Results and Discussion

Narrow-bore columns achieved comparable chromatographic resolution to conventional columns while reducing run times by:

• ≈52 % for free short-chain fatty acids (from ~6.7 min to ~3.2 min)
• ≈50 % for higher fatty acids methyl esters (from ~8.1 min to ~4.0 min)
• ≈60 % for higher alcohols (from ~11.1 min to ~4.4 min)

Retention times were highly reproducible (RSD < 0.25 %) and relative peak areas stable (RSD < 7 %) on both column formats. Real speed gains closely matched theoretical predictions once actual column lengths were considered.

Practical Benefits and Applications

Implementing 0.18 mm i.d. columns allows breweries and analytical labs to:

• Increase sample throughput by halving analysis time
• Utilize existing GC instrumentation without hardware overhaul
• Maintain analytical performance for routine monitoring of beer flavor quality

Future Trends and Opportunities

Further developments may include:

• Integration with advanced detectors (e.g., mass spectrometry) for enhanced selectivity
• Automation of sample preparation via on-column derivatization or online SPE coupling
• Extending narrow-bore approaches to other aroma and contaminant classes

Conclusion

Narrow-bore silica capillary columns (0.18 mm i.d.) provide a practical means to halve GC run times for critical beer flavor compounds while preserving separation efficiency and quantitative reliability. Their adoption can streamline quality control workflows without major capital investment.

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