Multiparameter hops analysis by near-infrared spectroscopy (NIRS)

Significance of the Topic

The accurate and timely assessment of hops quality parameters such as alpha acids, beta acids, cohumulone, total oil content, hop storage index (HSI) and moisture is essential to ensure consistent beer flavor and aroma. Traditional reference methods (titration, HPLC, steam distillation, UV-VIS and halogen drying) provide high accuracy but require extensive time, chemical reagents and specialized labor. Near-infrared spectroscopy (NIRS) offers a rapid, reagent-free alternative capable of simultaneous multi-parameter analysis, leading to significant cost and time savings.

Objectives and Study Overview

This study aimed to develop and validate NIRS calibration models for fresh hops and ground hop pellets to predict:

• Alpha acids (EBC 7.4, 7.5, 7.7)
• Beta acids (EBC 7.4)
• Cohumulone (EBC 7.7)
• Total oil content (EBC 7.4)
• Hop storage index (HSI)
• Moisture

The goal was to demonstrate that a single NIRS measurement (<2 min) can reliably replace multiple classical assays.

Methodology and Instrumentation

Over 500 samples (fresh cones and pellets) were scanned in diffuse reflection mode on an OMNIS NIR Analyzer Solid with rotating sample cups to address heterogeneity. Spectra were recorded and averaged automatically. Reference values were obtained by official EBC methods (titration, HPLC, steam distillation), UV-VIS photometry for HSI and halogen moisture analyzer for water content. Model development, calibration and validation were performed using OMNIS Software with external validation sets or cross-validation when sample numbers were limited.

Main Results and Discussion

All calibration models exhibited strong linear correlations (R²>0.95) and low prediction errors. A full-range alpha acid model (2.40–21.74 %) achieved robust performance across the concentration span. A focused sub-model for low alpha acid levels (2.43–4.26 %) reduced prediction error by half, illustrating the benefit of range-specific calibrations. Similar high accuracy was observed for beta acids, cohumulone, total oils, HSI and moisture. Rapid throughput (<2 min per sample) contrasts sharply with traditional methods taking up to 190 min for oil distillation.

Benefits and Practical Applications of the Method

• Simultaneous multi-parameter analysis without chemicals
• Significant reduction in analysis time and labor
• Lower ongoing costs and waste handling
• Non-destructive measurement enabling further use of samples

This approach is well suited for in-line or at-line quality control in hop processing facilities and breweries.

Future Trends and Potential Applications

Advancements in portable NIR devices and cloud-based chemometric platforms will facilitate real-time monitoring throughout the supply chain. Expanded pre-calibrated libraries for different hop varieties and integration with automation systems will further streamline quality assurance. Coupling NIRS with IoT sensor networks could enable predictive analytics for crop management and storage optimization.

Conclusion

NIR spectroscopy using the OMNIS NIR Analyzer Solid provides a fast, cost-effective and accurate tool for comprehensive hops quality control. The ability to tailor calibration models to specific concentration ranges enhances precision, making NIRS a valuable complement or alternative to traditional reference methods.

Reference

• EBC Method 7.4: Alpha and beta acids by titration
• EBC Method 7.5: Alpha acids in fresh hops
• EBC Method 7.7: Cohumulone determination