Stability is Critical

Temperature Stability of Catering Refrigeration is Critical in "Battle Between Working Kitchen Environment and the Equipment Used to Protect Food"

Article by Nick Tilley BSC (Hons) MSc MCIEH CMIOSH MSoFHT

Environmental Health Specialist and Director of Common Sense Compliance Ltd

One of the biggest issues I come across in the kitchen environment as an Environmental Health Practitioner is how to ensure that correct temperatures are being maintained for high risk foods. 

This article endeavours to explain firstly what is meant by food hygiene, how to control levels of bacterial food contamination and finally why the correct temperature of food is critical for food safety?

Some common problems seen in kitchens

As somebody who spends a lot of time in kitchens observing and discussing issues with Chefs, it is clear that there are a number of common problems that are seen. 

As we all know kitchens can be hot and humid places, which can allow ideal conditions for bacteria to grow. There always appears to be a battle between the working kitchen environment, and the equipment that is used to protect food and maintain good temperatures.

A good example of this is when fridge doors are opened. As we know cold air tends to sink and warm air rises; therefore when fridge doors are opened cold air will literally fall out of the fridge compartments and consequently be replaced by the ambient air in the kitchen, which is generally hot and humid.

This will lead to an unacceptable change of air temperature in the fridge. During busy service periods, when fridge/freezer doors are open and shut on a regular basis, air temperatures do not get the opportunity to recover and therefore the food temperatures will rise to dangerous and illegal levels. 

In addition to food temperatures, contamination control is vital. All too often poor standards of cleaning can allow food contamination to occur; especially on food contact surfaces and storage areas.

This can include mould build up on fridge door gaskets, dirt build up in difficult to access corners and areas which cannot be reached. It is very important that equipment is able to be cleaned properly; for example ensuring that there are no difficult corners which can harbour dirt, corners are coved and equipment is able to be dismantled easily to improve access for cleaning.

What is food hygiene?

The basic principle of food hygiene is simple: “removing or controlling the level of contamination on food to ensure it is safe to consume; from the “farm to fork”. 

What could be easier than that! 

Food can have a long journey from the farm to the plate. Therefore a number of key controls need to be carried out to ensure that food remains uncontaminated and is safe to eat. 

The type of contaminants that can affect food can be split up into a number of areas; from objects that are not expected to be on the food such as hair, dirt and mould, chemicals which can find their way into the food such as cleaning chemicals; to bacteria which can cause serious cases of food poisoning; for example Salmonella. 

The most common threat of all is bacteria. If allowed to flourish, some bacteria can cause serious cases of food poisoning, which can in turn lead to chronic conditions and in some cases death. This article focuses on how the food industry can remove or control bacterial contamination on food to assure its safety.

So how does food become contaminated with bacteria?

Bacteria is found everywhere in the environment, including the soil, the air, on animals and on people. This means that through the food journey there could be many opportunities for food to be contaminated with bacteria, from dirty equipment and poor food storage disciplines. Fortunately not all bacteria cause problems, however there are a significant number which will lead to sickness. 

These sickness causing bacteria are known as “pathogens” and will contaminate food by gaining contact directly on the food or being on or in the food through the “farming” stage.

How can contamination be reduced?

It is very difficult to remove all bacteria from food, as food is constantly exposed to the contamination within the environment. Therefore is it very important to ensure that the environment that the food is in allows for minimal exposure to bacteria and also does not allow the bacteria to reproduce to more hazardous levels.

How can the environment enable minimal exposure of bacteria?

Unfortunately, unless the environment is totally sealed; ie sterile then food will be exposed to some level of contamination. If these bacteria are then left in an environment which allows them to be comfortable, they will reproduce to a level which can become dangerous. 

So, the simple answer is to keep every surface that comes into contact with the food clean. These surfaces will include areas inside fridges which are poorly cleaned, compressor areas, tin openers, slicing blades, utensils and hands.

In addition hygienic handling and storage disciplines must be observed to ensure that bacteria is not allowed to transfer onto food. For example, common problems seen include allowing blood from a raw meat product to drip onto a “ready to eat” product or allowing hands to touch food directly after handling dirty fridge handles. 

As a general rule, there needs to be approximately one million bacteria present for food poisoning bacteria to cause problems. However there are some pathogens where the numbers of bacteria only need to be around 40 or even less. For example the E Coli 0157 bacteria only requires 40 and has been the cause of many serious food poisoning outbreaks over the years E. Coli can lead to permanent disablement and death; especially in the young.

So once contaminated how do the bacteria grow on the food?

When bacteria reproduce they physically spilt into two and this can happen between every 10 and 20 minutes; but the conditions have to be right. These conditions include having high risk foods; for example meat products, eggs and rice, with good levels of moisture available within the food and having time to reproduce at comfortable temperatures. 

So, one tiny bacteria can become over a million within two hours; that is fast.

How can food managers ensure the bacteria do not reproduce at that rate?

Whilst there are a number of different controls that are available to stop or reduce bacteria from multiplying, the most critical control that must be considered is the temperature profile of product. 

If high risk food (that is food which will happily allow bacteria to grow on them) is kept in the correct temperature parameters, then bacteria growth can be managed or even killed off altogether.

What are the correct temperature parameters?

Using the Celsius scale (°C) to measure temperature, bacteria are happy between +5°C and +63°C; and therefore simply by keeping the food outside this dangerous range the level of bacteria can be controlled. 

When food is stored below 0°C then the bacterial growth will slow down to zero growth. This means that food can be kept for a longer period of time compared to chilled food, although there can be issues with food quality.

When food is stored below +5°C then the bacterial growth is slowed to a rate which will ensure the food is safe for a longer period of time. This time period is normally a number of days and will be shown by the manufacturers “use-by” date, or for food produced on site, then a 72 hour rule should be considered; e.g. the food must be used within 72 hours. 

If food is to be cooked, reheated or held hot then it is important to ensure the food is above +63°C. The level of temperature required for cooking will depend on the time the food is held at that temperature. 

For example:

  • 60°C for a minimum of 45 minutes;
  • 65°C for a minimum of 10 minutes;
  • 70°C for a minimum of 2 minutes.

What are the legal requirements?

In simple terms; 

In England, Wales and Northern Ireland the chill temperature of high risk food must be at or below +8°C and hot food to be displayed at or above +63°C. It can be seen that there is a difference between the legal chilled requirement and the temperature that good practice recommends (Below +5°C). It is unclear why this difference exists but chill temperatures below +5°C should still be the target. 

In Scotland high risk food must be kept in a refrigerator or chilled area or at a temperature above +63°C. When reheating, food must have reached +82°C. 

However there is also the need for a food operation to have carried out their Hazard Analysis Critical Control Point (HACCP) plan, which will clearly have an impact on the temperature standards imposed.

So what should you be doing?

Control of contamination is vital, but it cannot be assumed that food is free from contamination; for example pathogenic bacteria; and therefore to ensure the food is safe for consumption the temperature profile of the product is critical and must form a basis of the HACCP management system. 

This means that high risk food which is delivered to any site must be in the appropriate temperature range: frozen food at a recommended temperature of -18°C and chilled food below +5°C. Food that is stored on site must be in the appropriate temperature range: frozen food at a recommended temperature of -18°C and chilled food below +5°C. 

Food cooked to the appropriate time/temperature: 60°C for a minimum of 45 minutes or 65°C for a minimum of 10 minutes or 70°C for a minimum of 2 minutes. It is vital to understand that the cooking process cannot be relied on to "clean up the food", as there other issues which can affect the foods safety. 

If cooled, then high risk foods must be cooled as quickly as possible to a temperature which will allow the product to be placed into a fridge safely (at least at ambient temperature but to +8°C or lower is ideal); and within 90mins. The use of a blast chiller is the most efficient way of achieving this. If food is to be reheated then it is recommend that the high risk food is reheated to above +75°C and only reheated once. When food is served then food should be above +63°C or below +8°C.


It is hoped that after reading this article, the management teams working within the food industry are reminded of the importance of temperature and contamination control and may feel the need to review their current arrangement. This may include looking at present practices, reviewing the menu to match up with the equipment available, review the current equipment provision or reviewing the current training programmes within the business.

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Common Sense Compliance Ltd
Tel: 01761 235604

Nick Tilley has over twenty years working in the Hospitality and Leisure industry, offering food safety, health and safety and fire safety management solutions.

Common Sense Compliance Ltd is an international provider of food hygiene, health & safety, fire management and leisure advice, with a growing client base servicing clients throughout the UK and internationally.