Optimizing Near-Infrared Spectroscopy for On-line Grape Must Quality Assessment: Addressing the Impact of Suspended Solids

What distinguishes good wine from premium wine is the quality of the berry material. The sugar and acid content are the key parameters in this case. To measure these, a timeconsuming and costly labor analysis is usually required during delivery process to the cellar. Near-infrared (NIR) spectroscopy offers a faster alternative, but is also used in laboratories due to its size and integrability. The development of the miniaturization of NIR-spectrometer opens up new possibilities for integration. To explore this, such a spectrometer and a pump with particle filter were integrated into a harvester to measure the quality parameters online during harvesting. The filter size of the pump that delivers the grape must to the NIR-spectrometer for analysis is a critical parameter as suspended solids in the must affect accuracy. This study examined the filtration requirements to reduce this problem using 38 samples from four grape varieties, filtered in 9 steps from 1mm to 40μm and centrifuged as the final step considered as free of suspended solids resulting in 359 spectra. Chemometric analysis via PLSR showed that, for sugar prediction, a finer filter is needed, whereas a proper preprocessing effectively eliminates the influence of solids on acids