Feasibility of Lactobacilli Concentration Detection in Beer by Automated Impedance Technique

Product quality is a primary concern in the brewing industry because the presence of high concentrations of bacteria can alter important organoleptic characteristics of the product (such as flavor and aroma defects and turbidity problems). Microbial concentration is usually measured by the standard plate count (SPC) technique, which produces accurate results but is slow and must be performed by laboratory tests with the aid of qualified personnel. This precludes the possibility of on-line monitoring of bacterial concentration at different steps of the production line. This study shows an alternative method based on impedance measurements, which proves to be competitive with SPC since it can detect the microbial concentration of 104 cfu/mL with measurement times as low as 10�12 hours against the 24�72 hours needed by SPC. It also features the possibility of industrial automation, thus making it very attractive for microbial screening on brewery production lines. Different media have been tested to obtain the highest bacterial growth rate (i.e., minimizing response time) and accuracy in lactobacilli concentration measured by electrical parameters. The need of selective determination of lactobacilli concentration has been achieved by adding cycloheximide to the samples and using filters of gradual size diameters to separate yeast cells from lactobacilli.