On-line roasted coffee quality control using NIR spectroscopy : [PF807]

Roasting is a key stage in the production of high quality coffee and this step must be controlled and reproducible to meet consumer expectations. The coffee organoleptic and physico-chemical characteristics have to be evaluated close to the process to assure fine monitoring of the roaster conditions. In 2006, a study was done in collaboration with Kraft Foods to evaluate the feasibility of using Near Infrared Spectroscopy (NIRS) to control coffee quality at discharge from the roasters. The study focused on moisture content determination using a NirOnline Xtwo spectrometer (Nir-Online, Walldorf, Germany). For this study, 284 samples of Arabica and Robusta coffees were roasted under industrial conditions and at the laboratory, and then remoistened to obtain a range of moisture content from 1% to 6%. Coffee beans were analysed in continuous mode using the Xtwo spectrometer and in a static mode using a FOSS 6500 laboratory spectrometer (FOSS, Port Matilda, USA). Calibrations were developed using partial least squares regression to predict moisture content of the coffee batches for each instrument. The performances in terms of accuracy and robustness of each calibration for continuous mode and for static mode were compared. The standard errors of prediction (SEP) of each calibration were similar, 0.18% for the FOSS spectrometer and 0.19% for the NIR-Online spectrometer. These levels of accuracy were very close to those obtained with the FOSS instrument for ground roasted coffee and to the standard error of laboratory reference method (SEL = 0.1%). This study confirms the possibility of at-line monitoring of the roasting step using near infrared spectroscopy. The next step will be the implementation of NIRS technology in the coffee roasting chain to automate and control the roaster parameters. (Résumé d'auteur