Ethanol content in wine by nearinfrared spectroscopy

Importance of the topic

Accurate determination of ethanol content is critical in winemaking for process control, product consistency and regulatory compliance. Traditional laboratory techniques such as gas chromatography require extensive sample preparation, chemical reagents and time. Near-infrared spectroscopy (NIRS) provides a rapid, non-destructive and reagent-free alternative that can be implemented either in-line during fermentation or in quality control laboratories.

Objectives and overview of the study

This application note describes the development and validation of a NIRS-based method for quantifying ethanol in red and white wine samples. The study aimed to demonstrate feasibility of rapid measurements, to establish a robust chemometric model and to compare performance against reference gas chromatography results.

Methodology

Wine samples covering a range of alcohol levels were measured in transmission mode across the near-infrared region (1000–2250 nm) using a 2 mm pathlength flow-through cell. A peristaltic pump facilitated automated sample delivery via the OMNIS Sample Robot S. Spectral data were processed and a calibration model developed using a leave-one-out cross-validation procedure to predict ethanol concentration.

Instrumentation used

• OMNIS NIR Analyzer Liquid covering 1000–2250 nm
• 2 mm quartz flow-through cuvette for transmission measurements
• OMNIS Sample Robot S with built-in peristaltic pump for automated liquid handling
• OMNIS Software with Quant Development module for data acquisition and chemometric model building

Main results and discussion

The NIRS calibration yielded excellent correlation with reference values, achieving a determination coefficient R2 of 0.995. Standard error of calibration (SEC) and cross-validation (SECV) were 0.080 and 0.082 % vol respectively. The high predictive accuracy demonstrates the suitability of NIRS for rapid ethanol measurement in wine without compromising precision.

Benefits and practical applications

The NIRS approach delivers analysis in under ten seconds per sample, eliminates the need for chemical reagents, and reduces operational costs. Its compatibility with automation platforms allows unattended processing of large sample batches. The method supports at-line monitoring in fermentation tanks as well as routine quality control workflows.

Future trends and opportunities

Advancements in portable NIR instrumentation and integration with process analytical technology are expected to drive wider adoption in winery automation. Enhanced chemometric algorithms and cloud-connected spectral libraries will improve model robustness and enable multi-component analysis. Opportunities also exist for extending NIRS to monitor additional parameters such as sugar content, phenolic compounds and organic acids in real time.

Conclusion

Near-infrared spectroscopy on the OMNIS platform offers a fast, reliable and chemical-free method for determining ethanol content in wine. The developed model demonstrates high accuracy and repeatability, supporting its use for both in-line process control and laboratory quality assurance.