Within this thesis, the optimization of piezoelectrically excited MEMS resonators for most precise sensing in liquid environment is targeted, ranging from 1 to 700mPa·s (for comparison: typical engine oil SAE 15W40 has 390mPa·s at room temperature). The advanced resonator design enables both, the actuation of the fundamental vibration as well as higher order modes. Additionally, a tailored electrode design for enhanced electrical read-out of specific modes facilitates high output signals. To further improve this sensing concept, the anchor structures of the resonators are optimized such that the nodal lines of the particular mode match the position of the mechanical fixtures, thus minimizing any losses to the silicon frame and enabling a quasi-free vibration. To quantify these concepts experimentally, MEMS resonators are fabricated using silicon micromachining technology including piezoelectric aluminium nitride as active material. The tailored read-out mechanism is utilized to excite and sense the first 10 orders of a special transversal bending mode named roof tile-shaped mode, which are electrically and optically characterized in air and several liquids by key device parameters such as the resonance frequency, the quality factor and the electrical conductance peak height in resonance. With this approach, a significantly enhanced performance is achieved for higher order modes, where a decrease in viscous damping of the fluid leads to increased values of the quality factor. Additionally, the signal to noise ratio (SNR) is enhanced by a factor of 50, when comparing the 10th with the 1st order mode. The implementation of an optimized support further increases the SNR by about 20% independent of the viscosity of the fluid. These three areas of optimization are of particular interest for sensing applications targeting either physical properties of high viscous liquids with dynamic viscosities >500mPa·s, or any mass changes on the resonator surface. In the last chapter of this thesis a potential application for this highly optimized sensor elements is introduced. Thereby, the piezoelectric excited resonators are used to monitor the minimal physical changes during grape must fermentation, enabling the distinction between ordinary and potential stuck fermentation processes.