Paolo De Censi, Khushwinder Singh, Alvaro Sanjuan, and Luca Brillante*
*Department of Viticulture and Enology, California State University Fresno, 2360 E Barstow Ave, Fresno, CA 93740 (lucabrillante@csufresno.edu)

Monitoring ripening is one of the most time-consuming laboratory procedures in grape and wine. The procedures are relatively long and complex and require extensive lab training and important labor expenses. The techniques are destructive and do not allow repeated measurements of the same samples. It is not possible to characterize spatial variability and the ripening process without large numbers of samples, thus incurring large costs. Hence, it is desirable to find new, faster techniques that are less expensive and produce spatial-temporal information to empower precise viticulture approaches. This study assessed grape skin flavonoids, total soluble solids, and titratable acidity in intact berries using a hyperspectral camera. The samples were collected in different vineyards and varieties to ensure a large variability in target compounds. In 2020, we collected ~400 samples of Cabernet Sauvignon and Cabernet franc berries in Madera, Paso Robles, and Rutherford, California, on different dates, but always after veraison. Samples were composed of 20 berries each. Each sample was imaged in a dark room in the lab using a VIS-NIR hyperspectral camera (500 to 900 nm), then peeled. From the flesh, we obtained juice for measuring total soluble solids and titratable acidity; from the skins, we obtained the anthocyanin pro- file through high-performance liquid chromatography. The reflectance spectra of the camera were related to the content in soluble solids, acids, and anthocyanins through random forest regression, and good correlations were found that predicted grape composition with a small associated error. These models will be deployed under field conditions by mounting the camera on a tripod, an ATV, or a conveyor belt for real-time monitoring of grape composition.

Funding Support: Bronco Wine Co., Fresno State Viticulture and Enology Graduate Assistantship