Characterization of Green, Roasted Beans, and Ground Coffee using Near Infrared Spectroscopy: A Comparison of Two Devices

Currently, the coffee production, starting from the entrance in the firm of the green coffee to the formulation of the final product, is highly automated. However, the ordinary analyses of moisture content, tap density and granulometry of the different semi-finished products aren’t integrated into the process, are time consuming and are not able to provide the analyses in real time. For these reasons, the aims of this study were to investigate the feasibility to use two near infrared spectrometers with the same optical bench (960-1650 nm), in order to characterize three mixture of coffee products (green, roasted, and ground coffee) for a future application directly at-line and in-line. For the analyses a benchtop In-Line Spectrophotometer (ILS) built for process measurement and a portable At-Line Spectrophotometer (ALS) were tested. Firstly, a qualitative analysis of the principal components was applied on the coffee spectra in order to evaluate the characterization feasibility for each matrix type during all steps of the process. In addition, the Partial Least Squares (PLS) regression analysis was applied to develop calibrations models to predict moisture content, tap density and powder granulometry on ground coffee and to estimate moisture on roasted bean with a view towards of real time measurements. The promising results, obtained in cross-validation, provided R2 values between 0.44 and 0.89 and between 0.21 and 0.71 for ILS and ALS, respectively. Finally, in order to compare the results obtained from the instruments, a Passing and Bablok regression and Bland-Altman analysis were performed. These analyses have showed that no significative differences are noticeable for the most part of data set analysed and for this reason both instruments could be applied in the productive process.