An assassin, that is how the biofilm is rightly called. These bacterial packages attach themselves to surfaces in the production line, are difficult to detect and can withstand a common cleaning process. The Flanders Research Institute for Agriculture, Fisheries and Food (ILVO) and KU Leuven map out the risks and look for solutions.
Bacteria that adhere to a surface can secrete polymers and thus form an extremely tenacious protective layer (extracellular matrix). In it they can multiply unimpeded without being detected by, for example, ATP tests.
Sometimes it goes well for years, until it breaks up and the bacteria ends up in the production process. As soon as a persistent biofilm has formed, the bacteria are well protected and resistant to most resources. Cleaning and disinfection is then often no longer sufficient.