Design, calibration, and validation of an inline green coffee moisture estimation system using time-domain reflectometry

Wet basis moisture content (MC wb ) is an important quality parameter of green coffee as it affects the coffee's physical, chemical, and sensory characteristics. Accurate estimation of green coffee MC wb after dry hulling, long-term storage, and transportation is imperative to prevent quantitative and qualitative losses. Thus, this study aimed to design, develop, calibrate and validate a prototype inline system capable of accurately measuring the MC wb of green coffee beans, using a commercially available time-domain reflectometry (TDR) probe. The TDR probe was calibrated and validated with green coffee within a MC wb range of 9–21%. A calibration linear regression model correlating the TDR probe output (dielectric constant) to reference MC wb measurements obtained by a halogen moisture analyzer, yielded a high coefficient of correlation (R 2 = 0.99). Model validation yielded a high R 2 , and a low Root Mean Squared Error equal to 0.93, and 0.9% MC wb , subsequently. Results indicate that the TDR inline green coffee moisture estimation system has the potential to be applied in real-time, industrial-scale operations. • An inline unit was built to measure green coffee moisture by time-domain reflectometry. • The system was calibrated and validated with reference to a halogen moisture analyzer. • Model validation yielded a high correlation ( R 2 = 0.93) with accuracy up to 91%. • The system performance is comparable to existing methods of moisture measurement. • The system has the potential to be applied in real-time, industrial-scale operations.