Novel approaches during industrial fermentation processes are not only restricted to classical pH, dO 2 and off gas analysis. There are many in-situ and online sensors based on different physical principles to determine biomass, product quality, metabolism and cell death. These process analytics are normally very cost intensive. One of the very important approaches relating to in-situ determination is the viable cell concentration (VCC). Based on this knowledge, an increased efficiency in monitoring and controlling strategies during cultivations can be provided. Electrochemical impedance spectroscopy (EIS) is a powerful tool in life science and has been heavily investigated for its potential to characterize the microbiological behavior during cultivation processes. For that purpose, EIS is used to monitor biomass in fermentation processes of Escherichia coli and Saccharomyces cerevisiae. A correlation of double-layer capacitance (CDL) and the cell density was found. The novelty of this approach has been proven with different stateof-the-art biomass measurements (dry cell weight (DCW) and optical density (OD)) in order to get an adequate verification of this method. Finally, it has been demonstrated that EIS measurement at low frequencies is a powerful monitoring tool in different modes (offline, online an inline) for microbiological cultivations. In addition to that, this approach is also perfectly suited to determining physio-logical states of the cells.

Advanced technologies, such as electrochemical impedance spectroscopy (EIS), are a valuable tool which can enhance and simplify the industrial process monitoring if used correctly. State-of-the-art approaches for screening the cell growth of for example yeast during the brewing process still heavily rely on offline methods such as methylene blue or florescence dye-based staining, and/or the usage of flow cytometric measurements. These methods, while being accurate, are very time consuming and require heavy manual effort. Furthermore, the time span needed to obtain the counting result can lead to a time-delayed response signal and can impact the quality of the final product. In recent studies, applications of low-frequency EIS in the α-regime were used for the determination of cell counts and the metabolic state in Saccharomyces cerevisiae. This method has proven to be a reliable tool which has also shown high potential in industrial scale applications. The online biomass monitoring, as well as viable cell count, for feasibility study was performed in-house at Stiegl Brewery in Salzburg/Austria founded in 1492.