Comparative study of hyperspectral imaging and portable spectroscopy techniques for selecting white grape pomace samples for fining agent production

During wine production, grape pomace is generated as a by-product. Although its management poses challenge due to its large volume, it also offers opportunities thanks to its high content of valuable biopolymers. However, not all pomaces share the same properties or are suitable for the same applications. In this study, a total of 111 pomace samples from three white grape varieties were studied: Pedro Ximénez ( n = 40), Moscatel ( n = 21), and Zalema ( n = 50). Spectral data were collected using three different devices: a NIR hyperspectral camera (900–1700 nm), a portable visible-NIR hyperspectral camera (400–1000 nm), and a MicroNIR portable spectrometer (900–1700 nm). Measurements were taken from both whole pomace and isolated grape skins, the latter being of particular interest for future research and possible application as natural fining agents. This generated six spectral datasets, which were subsequently merged into three augmented matrices to assess sample heterogeneity (matrix effect) and, subsequently, the impact of the measuring device (device effect). Each dataset was processed using Principal Component Analysis (PCA), and representative samples were selected based on the Mahalanobis distance to the nearest neighbour (NH). The results were compared to highlight the strengths and limitations of each instrument and sample type in achieving an efficient, cost-effective, and non-destructive selection method. Among the devices evaluated, MicroNIR proved to be the most cost-effective and portable solution for in-situ sample selection, enabling practical implementation in wineries. Finally, the selected samples were used as fining agents in red winemaking and their ability to clarify flavanols assessed. • Spectra of white grape pomace were recorded using three spectroscopic devices. • Seeds and stalks did not greatly affect the pomace spectral features. • MicroNIR device and pomace matrix were used for selecting representative samples. • The selected pomace samples were used and evaluated as flavanol fining agents.