Developments in Using Off-Line Radio Frequency Impedance Methods for Measuring the Viable Cell Concentration in the Brewery

Abstract

The radio frequency (RF) impedance method of measuring yeast concentration is accepted in many breweries around the world. The method relies on detecting the capacitance of the yeast cell membranes and gives a rapid linear response over a wide concentration range. The main application for the RF impedance method is for measuring the concentration of viable yeast in slurries; however the data presented also illustrate the use of the method for monitoring the yeast concentration during production fermentations. The variability of yeast growth during small-scale fermentations was also investigated for two lager strains. Batches pitched on the basis of capacitance were compared with those pitched using the traditional basis of wet weight. The small-scale fermentations pitched on the basis of capacitance were more reproducible than the fermentations pitched on the basis of wet-weight yeast. Good correlation was found between the capacitance and hemocytometer techniques in most small-scale and production vessels when the cell diameter was above 6 μm.