Combined Yeast Biofilm Screening – Characterization and Validation of Yeast Related Biofilms in a Brewing Environment with Combined Cultivation and Specific Real-time PCR Screening of Selected Indicator Species

Microbial spoilage of alcohol-free and low-alcohol beers, beer-mixed beverages, and soft drinks is most commonly caused by yeast. Yeast-related biofilms are therefore a serious problem in the production of these beverages. Fast detection of developing biofilms is a key factor to prevent subsequent spoilage of the product. For fast yeast detection, a new specific medium was developed and combined with real-time polymerase chain reaction (PCR) detection of characteristic beverage spoiling yeast species. The medium is based on MYPG broth (malt extract, yeast extract, peptone, glucose broth) with resazurin as a redox indicator for cell activity. The growth and biofilm potential of representative strains of commonly present beverage spoilage yeast species was evaluated using the developed medium. A novel real-time PCR detection system for Rhodotorula mucilaginosa, an early biofilm colonizer, was designed and successfully validated. Two field tests of the medium in combination with real-time PCR were performed. One test showed a differentiated hygienic status on a filler, and the other test tracked the contamination source of Saccharomyces cerevisiae var. diastaticus. Biofilm relevance of the strain set was proven. The modified MYPG proved to be highly sensitive when detecting yeasts. The detection of the selected target species directly in the medium was compatible and can provide detailed hygienic profiles when combined with additional information on the target species. This provides a fast detection method for yeast-related biofilms in brewery environments, differentiated hygienic monitoring, and makes it possible to troubleshoot contamination incidents.