surface disinfection

Surface disinfection

After the cleaning of surfaces and equipment there may be a need to reduce any residual micro-organisms present, to a safe level, by using a disinfectant.

Disinfection in the food and food service markets is the control of microorganisms that can cause harm to the consumer of the food product by pathogens such as Listeria, Salmonella and E. coli, or, cause the food to spoil, reducing its shelf-life and potentially making it un-wholesome through organisms such as Pseudomonas or Clostridium estertheticum. Disinfection is primarily undertaken for pathogen control, particularly in high risk areas of ready-to- eat (RTE) food producers but, is also undertaken in low and high risk areas for the control of spoilage microorganisms. Disinfection can be via thermal, physical and chemical means.

Thermal disinfection

Hot water or steam can be used to achieve disinfection and is a good method of doing so.  However, it is very difficult to achieve on large items of equipment in a food manufacturing operation so in the vast majority of circumstances chemicals will be used for disinfection.

Previous thinking about thermal disinfection recommended using hot water at 82°C for 30 seconds.  However, recent evidence has recommended that this is only achieved when using hot water at 90°C for a period of 60 seconds.  This method of disinfection tends to be restricted to tray wash machines, soak applications and CIP.

Steam disinfection of surfaces via a lance has had some success in certain environments but care should be taken as the steam can have an adverse effect on some plastics, paint and machinery and lubricants/grease.  They also pose a safety hazard to untrained personnel and could cause condensation to form on other equipment or surfaces.

In North America, larger pieces of open process equipment are being disinfected with steam by enclosing the equipment, in-situ, in plastic sheeting and introducing steam until thermocouple temperature probes establish that the equipment has reached a temperature from which a contact time can then be timed.

Physical disinfection

Physical disinfection via e.g. UV light, ionisation and cold plasma, are very rare in the food industry and used for very specific applications. UV light is the most practical but is only applicable to clean smooth surfaces that do not allow microorganisms to be shadowed from the light.

Chemical disinfection

Chemical disinfectants used in the food, beverage and food service sectors are designed to have low toxicity and taint profiles, working against the organisms of concern which are generally pathogens and food spoilage organisms.

It is crucial to follow the concentration and contact time recommended by the manufacturer, whilst ensuring an even coverage of the surface.

Where to disinfect

Disinfection is not applicable to all surfaces in a food manufacturing environment and should only be used on those surfaces where the presence of significant numbers of microorganisms will have an adverse effect on the safety and quality of the food handled.  If disinfection is deemed to be necessary, then the following areas should be considered:

  • Food contact surfaces
  • Operator contact surfaces
  • Cleaning materials and equipment
  • Hands
  • Evaporator components
  • Airspace
  • Drains and floors.
Choosing the correct disinfectant

The following factors should be considered when choosing a disinfectant:

  • Microorganisms to be destroyed
  • Contact time available
  • Type of surfaces to be disinfected
  • Risk of food taint
  • Toxicity of disinfectant and effect on personnel
  • Disinfectant method of application
  • Application temperature
  • Stability
  • Water hardness
  • Ionic nature of detergent used before disinfection.
Spray disinfection

Spray disinfection is the most common method for applying disinfectant to surfaces. It is versatile, gives good coverage and is an economic means of applying disinfectant solution.

It can be carried out by using a variety of different applicators. The most common are: small trigger sprayers, pump-up sprayers, compressed air driven sprayers, via a high pressure washdown system using a high pressure injector or via a medium pressure system.

It is important to consider the risk of liquid pooling. Poor equipment hygienic design features such as dead legs in closed processing systems, or undrainable areas of open processing equipment, may cause disinfectant solutions to pool. Such pooling can subject subsequent food products to high volumes of disinfectant which may enhance food adsorption of disinfectants.

Soak disinfection

This is probably the most effective means of disinfection as the item to be disinfected is fully immersed in the disinfectant solution, giving good contact time to all surfaces.  It is important that items are effectively rinsed as detergent residue or debris will inactivate the disinfectant. 

This type of disinfection method is usually confined to small items such as utensils, knives, blades, small machinery parts, cutting boards etc.

The disinfectant solution in the sink can be made up by using a wall mounted plunger dosing unit or a proportioning unit such as a venturi or Dosatron.