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.