Quantitative assessment of must composition using benchtop NMR spectroscopy: comparative evaluation with FTIR and validation by reference

Abstract

The foundation of wine production lies in the use of high-quality grapes. To produce wines that meet the highest standards, a fast and reliable analytical assessment of grape quality is essential. Many wineries currently employ Fourier-Transform Middle-Infrared Spectroscopy (FTIR) for this purpose. However, this technique demands frequent and intricate calibration with authentic reference samples, and its indirect quantification approach raises concerns about reliability for certain parameters. Additionally, FTIR has high detection limits for key indicators of grape rot, such as gluconic acid and volatile acids.

Nuclear magnetic resonance spectroscopy (NMR), on the other hand, enables the direct measurement of these compounds, eliminating the need for calibration and enabling precise quantification. However, conventional high-field NMR systems are associated with high acquisition and maintenance costs, limiting their widespread use. Continuous development has optimised benchtop NMR spectrometers providing a cost-effective alternative. Although these devices operate at lower magnetic field strengths and therefore have reduced resolution, they are a viable alternative. To overcome this limitation, we use a spectral correction and peak analysis algorithm based on quantum mechanical calculations and pattern recognition [1,2].

In this study, the must components were analysed quantitatively using benchtop NMR. The results obtained were compared with FTIR measurements and validated against established reference methods, including photochemical and titrations. The measurements showed good agreement with the reference values, demonstrating higher precision and possibly even better accuracy than conventional methods. This is to be verified in more detail by further gravimetric investigations. In addition, the sample preparation process was considerably simplified, as initial tests showed insensitivity to known interfering factors such as turbidity. This indicates a robust and efficient analysis method with reduced preparation effort.

Our results suggest that this method could be integrated into automated grape reception processes, allowing wineries and cooperatives to obtain important quality data in a timely manner. Further validation is required in order to conclusively assess its suitability for routine use.

References

[1] Matviychuk, Y., Haycock, S., Rutan, T., Holland, D. J. (2021). Anal. Chim. Acta, 1182, 338944.

[2] Phuong, J., Salgado, B., Heiß, J., Steimers, E., Nickolaus, P., Keller, L., Fischer, U., Harbou, E. von, Holland, D. J., Jirasek, F., Hasse, H., Münnemann, K. (2025). Food Res. Int., 203, 115741.