Microbial attachment and biofilm formation in brewery bottling plants

Microbiological risk management is essential in the production of high-quality beer since quality defects may lead to substantial economic losses. The hygiene of process surfaces essentially affects the quality of the final product. The brewing industry is prone to biofilm formation due to the abundance of water needed at every stage of production. Biofilms develop when attached microorganisms secrete extracellular polymers, which in turn protect them effectively against cleaning and sanitation. In the current study, sterile stainless steel coupons were mounted onto critical sites of the fillers in three brewery bottling plants. Microbiological samples were taken from the coupons to reveal the pioneer organisms in biofilm formation. Microbiological samples were also taken from different horizontal and vertical surfaces close to the open product at the filler and crowner in order to be able to compare the microflora on the coupons with process surfaces in use. The pioneer bacteria were identified by ribotyping, carbohydrate fermentation tests, and partial DNA sequencing. The effect of sugars and sweeteners on attachment of pioneer organisms to stainless steel was studied in 1 mM phosphate buffer and analyzed by epifluorescence microscopy. The biofilm formation rate was studied for 8 weeks by successively dislodging the test coupons from each sampling site and examining them by epifluorescence microscopy. The results showed that pioneer microbes accumulated on new stainless steel surfaces within hours after the start of production. Regular daily cleaning reduced the number of microorganisms on the surfaces only momentarily. Canning machines were markedly less prone to accumulation of microorganisms than bottling machines. Gram-negative bacteria, yeasts, and molds were the first to colonize the surfaces. Attachment of pioneer species to stainless steel was increased substantially by sugars and, surprisingly, also by intense sweeteners. Horizontal surfaces were prone to microbial accumulation and should be avoided in constructions as much as possible. Furthermore, biofilm formation occurred on certain surfaces despite daily cleaning and disinfection.