Optical monitoring of wine alcoholic fermentation using a non-specific NDIR microarray

A compact and affordable instrument, based on a modified non dispersive infrared (NDIR) optical scheme, has been used for the monitoring of the wine chemical evolution throughout the alcoholic fermentation process. A qualitative trial with commercial samples of must, wine (red and white) and vinegar has proved the instrument ability to discern the grape derivatives, and confirmed its suitability as prospective tool for real time in-line monitoring of wine processing. Instrument capacity to predict significant parameters of wine samples has been ascertained in micro-fermentation trials conducted during 2013 vintage harvest in the Penedés (Catalunya) viticultural area. A set of wine samples were obtained at different stages during fermentation and spectral data were achieved with the NDIR instrument. Same samples were also analyzed by using chemical methods to evaluate the sugar (glucose and fructose), alcohol (ethanol and glycerol) and wine density. The pretreated spectral data were processed using principal component analysis (PCA). Results show that samples belonging to a particular fermentation stage, from initial to final phase, could be correctly classified. Moreover, partial least square (PLS) regression was used to predict wine parameters like sugar content, ethanol and density simultaneously. Calibration models for the prediction of the main compositional changes during alcoholic fermentation were obtained with the NDIR data, suggesting that the instrument could be used to evaluate online and simultaneously these compounds in wine processing.