FERMENTATION CONTROL USING ATR AND AN FT-IR SPECTROMETER

Several sensors (gas, temperature, density, near-infrared) have been tested to give on-line real-time information on the composition of a must during fermentation, but it is still impossible to monitor the concentration of the individual sugars (fructose and glucose). Our purpose is the development of an on-line real-time sensor in order to control the fructose and glucose contents during fermentation. A Fourier transform mid-infrared (FT-IR) spectrometer equipped with an attenuated total reflectance (ATR) accessory is used. The spectra of more than 180 samples extracted from 12 fermentations are recorded and the glucose and fructose concentrations are enzymatically measured. The spectra are processed by the inverse multilinear regression method (also called the P matrix regression method), the principal components regression and the partial least squares (PLS) methods. Best results are obtained with the PLS method and then with inverse multilinear regression. The minimum standard error of prediction is 1.1 g/l for the glucose in a segmented regression.