Developing a handheld NIR sensor for the detection of ripening in grapevine

It has already been proven that near infrared (NIR) reflectance spectroscopy can be used to measure the ripeness of grapes by the determination of reducing sugar and acid contents. Until now, winegrowers need to collect a random one hundred berries sample per plot, to measure these parameters destructively for the estimation of the ideal harvest time of the gained product. Meanwhile, inexpensive sensors are available, to build convenient instruments for the non-destructive, low-priced and fast control of ripening parameters in the vineyard. For this, a small device including a NIR sensor (900 nm - 1700 nm / 1300 nm - 2600 nm) was built from a Raspberry Pi 3 and a NIR sensor. Spectra of individual berries, sampled from six different Vitis vinifera (L.) cultivars (Riesling, Chardonnay, Pinot Noir, Dornfelder, Pinot Gris and Dakapo) were collected. Corresponding reference data were determined with high performance liquid chromatography (HPLC). Samples were taken from different fruit-, as well as cluster zones and from the beginning of veraison until after harvest, to ensure a broad range of ingredients and the ripening properties of different berries from the vine. White, as well as red varieties were used to establish the built sensor as a viable tool for ripening prediction for mainly cultivated vines. Spectra of teinturier berries with strongly coloured flesh or skin were collected to verify its accuracy for these cultivars, too. This study is the first that systematically investigates the ripening parameters of a whole vineyard with a handheld sensor. The sensor can be used in viticulture practice to detect the ripening process and ideal harvest time due to effectiveness and simplicity.