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

•This work presents a novel approach for the monitoring of a grape must fermentation process with a piezoelectric MEMS resonator excited in the 4th order of the roof tile-shaped mode.•We measured the fermentation kinetics by simultaneously tracking the resonance frequency and the quality factor of the microresonator. Once these two parameters are known, the viscosity and density of the liquid can be determined.•A calibration procedure of the resonator was performed using model solutions of artificial grape must representing an ordinary (for calibration) and a stuck or sluggish (for validation) fermentation process and a commercial density-viscosity meter. Furthermore, an in-line flow-through monitoring of a grape must fermentation was carried out.•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 1 mg/ml and 20 μPa·s as upper limits for the density and viscosity, respectively.

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 1 mg/ml and 20 μPa s as upper limits for the density and viscosity, respectively.