A Multipurpose Portable Instrument for Determining Ripeness in Wine Grapes Using NIR Spectroscopy

Abstract

This paper describes the development of a noninvasive instrument that is designed to measure three parameters of ripeness in wine grapes, i.e., sugar (Brix), pH, and anthocyanin concentration. The instrument is based on near-infrared spectroscopy, and it comes in contact with the berry in the cluster without altering its ripening process. A thorough description of the calibration process for the instrument is done for the different grape varieties, e.g., Cabernet Sauvignon, Carmenere, Merlot, Pinot Noir, and Chardonnay. Samples from vineyards located in the Maipo Valley (Chile) taken during the 2003 season were processed to develop calibration models using partial least squares techniques. The models were validated in terms of root mean square error of validation and R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> indices. The results show the great potential of this technique regarding Brix and pH measurements. For the anthocyanin concentration measurements, the results are promising but require an accurate procedure to obtain reference values for model calibration. The instrument can be useful for sampling strategies that look for optimum harvest schedules according to grape maturity in terms of not only sugar content but also pH and anthocyanin concentration.