Decontamination using heat

Below we provide information on the decontamination of equipment using heat.  This information comes from a study by Tompkin (2002). Tompkin (2002) provided advice for the decontamination of processing equipment that was known, or suspected to be contaminated with L. monocytogenes.   It is apparent that to sanitise equipment harbouring L. monocytogenes, it would usually be sufficient to disassemble the equipment then clean and sanitise the parts using specialist chemicals.  An important finding of the study was that although there is merit in exceptionally thorough cleaning using increased concentrations of chemicals, such an approach was not always effective.  In older equipment, that may not have been designed for effective decontamination, there can be L. monocytogenes niches that are poorly penetrated by sanitisers.  Examples of such niches includes hollow or ball bearing-filled rollers on conveyor belts, equipment support rods, the space between metal-to-metal joins (Figure 1A), worn or cracked rubber seals around chiller doors, particularly if the chillers are prone to condensation, equipment controls and door handles and places that are wet (Figure 1B).

Figure 1:  Examples of niches with the potential to contain plant resident strains of L. monocytogenes. A) metal-to-metal joints; B) wet and corroded collar and screws.

On those occasions when a chemical treatment was ineffective, Tompkin (2002) advised either the replacement of the contaminated item, or an equipment-specific application of heat.  For small pieces of suitable equipment, immersion in a hot (>80oC) water bath containing detergent was reported as reliably effective (Tompkin 2002).  For equipment that was larger, contained water-sensitive electronics or greased parts, heat could be applied by moving the equipment into a product-baking oven. 

For equipment that was too large for an oven, Tompkin (2002) advised that any electronics were removed, the equipment was covered in a heat resistant tarpaulin and steam applied from the bottom.  The previous experiences of the project team were that inexpensive (£20-30) steam generators of the type used to remove domestic wallpaper performed exceptionally well when used to decontaminate industrial equipment.  Tompkin considered that a target temperature of 71oC should be achieved for at least 20 minutes in order to achieve effective equipment decontamination.

Tomkin, R. B. (2002).  Control of L. monocytogenes in the food-processing environment.  Journal of Food Protection 65, 709-725