The acoustic impedance - An indicator for concentrations in alcoholic fermentation and cleaning progress of fouled tube heat exchangers

For processing foodstuff such as alcoholic fermentation it is crucial to determine values like sucrose and ethanol concentrations fast, easily, and online to maintain quality standards. Also, to maintain hygienic standards cleaning of used process equipment is necessary. In dairy industry this is done via Cleaning-in-Place cycles which are often inflexible and difficult to monitor. For both a powerful monitoring method is needed. Ultrasound is suitable and can be used non-invasively to get accurate information in real time. Often sound velocity is analysed but alternatively the acoustic impedance can be obtained to get information about the sample state. Our innovative method is based on integrating the intensity of multiple reflections of the first echo at the first interface. Thereof a straight line over number of reflection can be plotted whereby the slope determines the reflectivity and therewith the acoustic impedance of the substance behind the stainless steel wall. Using pulse-echo mode a clear linear dependence of the impedance of sucrose-water mixtures on sucrose concentration is determined. With rising concentration the impedance rises, too. On the other hand the impedance of ethanol-water mixtures shows a more complex behaviour. This is due to the fact that the density decreases whereas the velocity of sound first increases and at 25 mass percentage ethanol starts to decrease. Also, the presence of milk fouling on a heated surface can be detected definitely using acoustic impedance.