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

Abstract

tThe traditional procedure followed by winemakers for monitoring grape must fermentation is not auto-mated, has not enough accuracy or has only been tested in discrete must samples. In order to contributeto 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 rooftile-shaped vibration mode. Furthermore, conditioning circuits were designed to convert the one-portimpedance of the resonator into a resonant two-port transfer function. This allowed us to design a PhaseLocked Loop-based oscillator circuit, implemented with a commercial lock-in amplifier with an oscillationfrequency determined by the resonance mode. We measured the fermentation kinetics by simultaneouslytracking the resonance frequency and the quality factor of the microresonator. The device was first cali-brated with an artificial model solution of grape must and then applied for the in-line monitoring of realgrape must fermentation. Our results demonstrate the high potential of MEMS resonators to detect thedecrease in sugar and the increase in ethanol concentrations during the grape must fermentation with aresolution of 1 mg/ml and 20 Pa s as upper limits for the density and viscosity, respectively.