Improved quality control and moisture determination in dry kava ( Piper methysticum ) from Vanuatu: a practical oven-drying approach

Dry kava ( Piper methysticum ) exports in the Pacific Island region are booming, but stringent quality control remains a critical factor in maintaining the reputation and competitiveness of these exports in international markets. This study evaluates trends in the quality of dry kava export in Vanuatu, develops a practical Association of Official Analytical Chemists (AOAC) oven-drying method for moisture analysis, and assesses the effects of drying on dried kava samples and colorimetric absorbance. A national database of colorimetric absorbance measurements from 2016 to 2024 was analysed, using the benchmark that high-quality “noble” kava has a maximum absorbance threshold value of 0.84 ± 0.05, according to previous studies. For moisture determination, kava samples were dried at 105 °C in an oven for 0.5 h, 1 h, 1.5 h, and 2 h, and compared against the infrared (IR) thermal combustion method, with further verification by Fourier Transform Infrared (FTIR) spectral analysis. Results indicate that kava quality in Vanuatu has significantly improved, with absorbance values decreasing from 0.72 to 0.48 (2016 to 2024), indicating stronger quality control across the export chain. The 2 h oven drying method closely matched the IR method with high agreement (R-Square (R2) = 0.99, Bias = 0.12%, Precision = 0.2%, Root Mean Square Error (RMSE) = 0.20). It also demonstrated better repeatability (Relative Standard Deviation (RSD) = 0.22%) and strong reproducibility (RSD = 0.29%). The FTIR analysis indicated minimal spectral variation among samples dried for 2 h, suggesting that only limited chemical modifications occurred during this drying stage. In contrast, pronounced spectral shifts were observed at 1,050, 1,640, 1,740, and 2,920 cm 1 after 4 h of drying, reflecting substantial alterations in the chemical composition of the kava samples. The samples achieved a constant weight after 4 h of drying at 125 °C and 131 °C, exhibiting significantly greater weight loss compared to those dried at 105 °C for the same duration. Furthermore, a significant correlation ( p ≤ 0.05) between colorimetric absorbance and weight loss was observed, indicating that moisture content strongly influences optical properties thereby supporting more accurate nobility assessment. These findings demonstrate that the 2 h oven drying method at 105 °C is a practical and reliable approach for routine moisture analysis in dry kava and can support improved quality control in the kava industry.