Cooling

Keep cold food cold to prevent food poisoning

: Keep cold Food cold to prevent Food poisoning

Temperature control must be strictly adhered to ensure the safety of food on the receipt, storage, preparation, cooking and serving of ingredients. The temperature danger zone is between 5 and 63 degrees Celsius. Food, after preparation and cooking, must be kept out of this zone. When hot food has been cooked, it must be retained above 63 degrees to remain free from bacterial growth. Food Safety pathogens will not grow above this temperature. Once food is cooked to 75 degrees C it is safe to eat, all bacteria have been killed. If food is retained at the correct hot-holding temperature, it can be served indefinitely, as it is going to remain safe at that temperature. (Although food quality would be greatly affected by retaining it for that length of time!). No vegetative pathogens will survive temperatures above 60 degrees C, so perhaps cooking to 75 is slightly overkill.

If high risk food is being served cold, it must be refrigerated between 1 and 4 degrees C and held at that temperature until served. Sandwiches and baguettes with protein fillings, pork pies, pates, cold meats, seafood, etc can all cause food poisoning if left at warm temperatures, as any bacteria or spores present will start to grow to dangerous levels. (Spores would only grow as vegetative pathogens after germinating.) It is the vast numbers of bacteria that cause food poisoning. Foodborne diseases are caused by fewer bacteria, which are termed low dose pathogens.

Although there is no time limit to how long hot food can held, from a food safety point of view, cold food can prove to be a problem if held for too long at refrigeration temperatures. Moulds, for example, can start to grow on food within several days, even in very cold conditions.

In the UK, the Four Hour Cold Rule can be used to good effect if there is a rapid turnover of cold food or if refrigerated storage breaks down. If, for example, a batch of sandwiches are prepared for service to the public, and is held in refrigerated display, and that equipment was to subsequently break down, the temperature of the food would start to increase to within the temperature danger zone. In those circumstances, one would be allowed to sell the sandwiches for a maximum of 4 hours from the time of preparation. If any remain after the 4 hours, they must be disposed of.

Some baguette/sandwich companies, which have a quick turnover of product, such as in train stations and airports, are allowed to sell their wares without refrigerating their products, due to this ruling. This ensures the sensory qualities of the food are enhanced. (There is nothing worse than cold rolls or baguettes).

This 4 hour ruling can be considered to be a food safety hazard, however, especially if buffet items are festering for 4 hours, after being prepared, in a warm room. If there are already bacteria present, which there will be, (from handling, environmental particles, cross contamination), they can multiply quite significantly in 4 hours. Bacteria can double in size every 10 minutes. In four hours bacteria will double in size 24 times. If only 10 bacteria are present at the start of the 4 hours, 10 to the power of 24 bacteria will grow in that time. (That is quite a few! In the order of trillions. It only takes 10 to the power of 6 Salmonella to cause food poisoning).

For further information on food safety, the prevention of food poisoning, cleaning, pest control, personal hygiene and legislation go to Food Safety.

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Cooling Is As Important As Cooking In Ensuring Food Safety

If a product has been cooked and it is to be used cold, then it must be chilled down as quickly as possible. The temperature danger zone is 5 to 63 degrees Celsius. This is the zone where Food must be kept out of after preparation. Cold Food must be held at less than 5 Celsius, to prevent microbial growth, which is critical to food safety. Some pathogens, such as Listeria monocytogenes, will grow in a fridge, but the majority, which are called mesophiles, prefer temperatures in excess of 15 degrees. The optimum temperature is around 37 C. (Body temperature).

There are several ways that the product can be cooled quickly and safely. Blast chilling is a very efficient method of cooling. This process uses forced cooled air, continually blasted over the food until it reaches <5 degrees Celsius. The process usually takes up to 90 minutes. There are other ways to achieve the cool temperature, but most take longer than 90 minutes. The Campden system allows for food to be cooled in stages. This process can take up to 8 hours. The American system allows up to 6 hours in stages.

So, the quicker the better, from a food safety perspective. What if blast chillers are not available and the American or Campden system is being utilised? How can the food be cooled quickly.

Use small joints, no bigger than 2.5 kilos.

If the food is liquid based, such as a curry, stew or casserole, then decant into shallow containers for cooling. This gives a larger surface area, which will cool down more quickly than a deep saucepan, for example.

After removing the food from cooking, leave it in a cool room, for no longer than 90 minutes, then refrigerate.

Ensure the fridges are fan operated, to allow more even circulation of cool air.

Once the food is cooled, it must be maintained at a temperature of 1 to 4 degrees Celsius to ensure food safety. The fridge must be regularly checked throughout the day to ensure this. Certainly in an operation, such as a restaurant, which opens for 8 hours, the fridges must be checked at least 3 times during the 8 hours. This is best achieved using a thermocouple temperature probe. It is a tip sensitive, digital thermometer which is capable of being calibrated. The concern must be with the product temperature and not the air temperature. Digital temperature displays on fridges, or probes retained in fridges are not adequate systems for temperature monitoring. It has been found that the best method is to retain a glass/cup of dry salt on the top shelf of the fridge and to insert the probe into the salt throughout the working day.