Flow-through sensor based on piezoelectric MEMS resonator for the in-line monitoring of wine fermentation

Abstract

The traditional procedure followed by winemakers for monitoring grape must fermentation is not automated, has not enough accuracy or has only been tested in discrete must samples. In order to contribute to the automation and improvement of the wine fermentation process, we have designed an AlN-based piezoelectric microresonator, serving as a density sensor, resonantly excited in the 4th-order roof tile-shaped vibration mode. Furthermore, conditioning circuits were designed to convert the one-port impedance of the resonator into a resonant two-port transfer function. This allowed us to design a Phase Locked Loop-based oscillator circuit, implemented with a commercial lock-in amplifier with an oscillation frequency determined by the resonance mode. We measured the fermentation kinetics by simultaneously tracking the resonance frequency and the quality factor of the microresonator. The device was first calibrated with an artificial model solution of grape must and then applied for the in-line monitoring of real grape must fermentation. Our results demonstrate the high potential of MEMS resonators to detect the decrease in sugar and the increase in ethanol concentrations during the grape must fermentation with a resolution of 1mg/ml and 20μPas as upper limits for the density and viscosity, respectively.