Multiparameter hops analysis by near-infrared spectroscopy (NIRS)

Significance of Topic

Near-infrared spectroscopy (NIRS) offers a rapid chemical-free approach for the critical quality control of hops across the brewing supply chain. It addresses limitations of conventional titration, HPLC, and photometric assays by reducing analysis time, labor intensity, and reagent usage.

Objectives and Study Overview

The study aimed to develop and validate NIR-based predictive models for key hop parameters: alpha acids (various EBC norms), beta acids, cohumulone, total oil content, hop storage index (HSI), and moisture in fresh hops and ground pellets using an OMNIS NIR Analyzer Solid.

Methodology and Instrumentation

The experimental workflow involved:

• Analysis of over 500 fresh hop samples and ground hop pellets in diffuse reflection mode with rotating sample cups to capture spectral variability.
• Spectra acquisition, model development, and validation executed with OMNIS Software.
• Reference methods: EBC 7.4, 7.5, and 7.7 for acids and oils; halogen moisture analyzer for moisture; UV-VIS photometer for HSI.

Instrument Used

• OMNIS NIR Analyzer Solid (Metrohm): near-infrared spectrometer for rapid, multi‐position measurements of solids and viscous samples.

Main Results and Discussion

• Robust calibration models achieved high correlation between NIR predictions and reference values for all parameters, validated by external or internal cross‐validation.
• Alpha acid models covered full (2.40–21.74%) and narrow (2.43–4.26%) ranges; narrowing improved prediction error twofold.
• Cohumulone, beta acids, total oil content, moisture, and HSI models demonstrated strong predictive performance reflected in figures of merit (RMSE, R²).

Benefits and Practical Applications

• Analysis time reduced to approximately 2 minutes for all parameters versus 7–190 minutes by traditional methods.
• No chemical reagents required, lowering consumable costs and waste.
• Minimal sample preparation and automated rotation yield reproducible results suitable for routine QC in breweries and hop suppliers.

Future Trends and Potential Applications

The integration of pre-calibrated NIR models, automated workflows, and cloud-based spectral databases can further streamline hop analytics. Expanding NIRS to additional raw materials and process intermediates will enhance digitalization in the brewing industry.

Conclusion

NIRS with OMNIS NIR Analyzer Solid provides a fast, cost-effective, and reliable alternative to classical methods for comprehensive hop quality assessment. Tailoring calibration models to specific concentration ranges can further optimize accuracy.

References

• Application Note AN-NIR-130: Multiparameter hops analysis by near-infrared spectroscopy.
• EBC 7.4. Determination of bitter substances in hops and hop products.
• EBC 7.5. Determination of cohumulone in hops.
• EBC 7.7. Determination of alpha acid isomerization and cohumulone.