Characterisation of biofilm hotspots at a can filling line for beer

Biofilms are thought to play a serious role in the food processing environment. Direct contact with or detachment of microorganisms of biofilms could lead to product contamination resulting in diminished shelf life of the product. Packaging and filling are essential key steps for product safety, as any contamination within this step will directly impact the shelf life and safety of the product. For bottled and canned beverages filling lines are used for filling huge amounts of product in a standardised manner. Most parts of these lines are cleaned and disinfected automatically during cleaning in place (CIP) procedures. The design of these filling lines is of great importance, as accessibility and materials are crucial regarding the success of automatic cleaning and disinfection programs. Some companies implemented additional manual cleaning strategies for the complete removal of potential problem-causing sites. In the brewery setting the term biofilm is manifested since the 90s. However, until now all studies focus only on the presence of microorganisms, neglecting the presence of matrix components, which constitutes an essential component of a biofilm.  

Within this study a filling line for cans, capable of filling 60000 cans per hour (volume 0.5 l), was investigated regarding critical sites for biofilm formation. The filling line is used primarily for beer, but mixed beer drinks are also filled. We sampled 23 sites using a scraper-flocked-swab method at two time points. The first sampling was done during operation and the second sampling was conducted one month later after the automated cleaning and disinfection procedure. The samples were characterised regarding their microbial load (qPCR for 16S rRNA and 18S rRNA genes) and the presence of biofilm matrix (phenol-sulfuric assay for carbohydrates, precipitation and SDS-PAGE with subsequent silver staining for proteins and precipitation and spectrophotometric quantitative measurements for extracellular DNA).

During operation, we could identify three sites harbouring a biofilm by applying the definition of presence of microorganisms and at least two matrix components. Furthermore, there were seven sites harbouring microorganisms and one matrix component. After cleaning and disinfection no biofilm could be detected. At one site, microorganisms and one matrix component could be detected. The drastic reduction of biofilm positive sites indicates the successful removal of biofilms by the cleaning and disinfection process.

The design of future filling plants should emphasise on the principles of hygienic design, as this can help to prevent biofilm formation and targeted removal of biofilms during cleaning and disinfection. The here identified biofilm hotspots indicate potential problem-causing sites and weak-points in the design of the filling line.