Chilling facts: the need for ‘practical’ safe practice

Abdul Rashid is the regional director for the GCC, Middle East & Africa at JohnsonDiversy Dubai.

The theme of this month's third Dubai International Food Safety Conference is Food Safety: Know it Right, Do it Right, which brings together food safety professionals, food scientists and regulators to address food safety issues and focus on working together to enhance safety of the global food supply.

With this in mind, I want to discuss the discrepancy between the advice given on the safe chilling of cooked foods and practical, scientifically-based facts regarding the cooling of cooked foods.

Conventionally, we are advised that to cool chilled foods safely, chilling must take place in less than 90 minutes before food is put in a fridge. But is chilling in 90 minutes really possible? And has it been successfully demonstrated for different recipes and quantities of food within a confined space of time?

The idea of the 90-minute guideline does not appear to be based on sound science. Recent developments in food safety management toolkits have shown that, if safe methods are adopted, cooling may safely take longer than 90 minutes.

How then did 90 minutes become the benchmark for chilling cooked foods quickly? If a small business has the luxury of a blast chiller then chilling cooked food to below 10°C in 90-minutes or less is reasonable to expect. But food safety management specialists and chefs know that 90-minute chilling is not always practical in a small business that does not have a blast chiller.

Effective response to the challenges of food-borne illness can only be achieved once the common understanding and law on which food safety decisions are made is based on the biochemical realities and bio-facts of organisms.

Differences of opinion

The "danger zone" ranges vary internationally. In the UK, it is 8°C to 63°C. In Australia and most other countries, it is 5°C to 60°C and in the US the danger zone is 5°C to 57°C. The scientific maximum and minimum temperatures for the multiplication of food pathogens is -2°C to 52°C. The most rapid multiplication for common food-borne pathogens is 20°C to 50°C.

In Australia, the advice is to cool food within two hours from 60°C to 21°C and from 21°C to 5°C within four hours before putting it in a fridge. The US FDA allows almost the same time while Codex states the temperature in the centre of the food products should be reduced from 60°C to 10°C in less than two hours and the product stored below 4°C.

Effective safe cooling depends on a number of factors including the type of organisms that need to be destroyed or controlled; the density of the food; the volume of food; the type of container, and the ingredients used. Research in the US and UK has shown the cooling of certain foods to below 10°C in 90 minutes is unlikely to be achieved in catering businesses where blast chilling equipement does not exist.

Cooling does not need to start on the immediate removal of cooked food from an oven. Clostridium perfringens will stop multiplying above 52°C and other organisms are destroyed at lower temperatures.

But this can only be safe if cooking, chilling and so on are applied throughout all stages of recipe production. The 90-minutes rule is fine for thinly spread out medium to high-risk foods or the recipes they may be used for in a small and less developed catering businesses and outlets.

The Food Standards Agency in the UK suggests cooling food as quickly as possible. Its Safer Food Better Business (SFBB) toolkit does not even mention 90-minutes. It states that, "harmful bacteria can grow in food that is not chilled down as quickly as possible", and provides options for chilling foods, such as adopting safe cooking methods and preventing cross-contamination of the food product.

Food handlers on food safety training courses need to be advised about alternative methods of chilling and the precautions they should take to cool foods quickly and safely. It would be unwise to rely solely on the 90-minute cooling time yardstick because it is not practical for the majority of small catering businesses. There is a fine balancing act between promoting theoretical safe practice and practical safe practice.

Practical tips

Alternative safe and practical solutions should be provided. These include:

• Preventing recontamination by removing the risks associated with cross-contamination.

• Giving special consideration to large food items, such as roasts, turkeys, thick soups, stews, chili and large containers of rice or refried beans.

• Reducing the volume of food in an individual container and keeping the cover loose for the heat to escape (which speeds the rate of cooling).

• Using rapid chill refrigeration equipment designed to cool the food to acceptable temperatures quickly by using increased compressor capacity and high rates of air circulation.

• Avoiding the need to cool large masses of food by preparing smaller batches and making sure they are closer to services.

• Stirring hot food while the food container is within an ice water bath.

• Re-designing recipes so that they are prepared and cooked in a smaller or concentrated base and with enough added cold water or ice to make up the volume required (e.g. water-based soups)

Food safety has to be based on practices that can be easily and practically applied to the kitchen operations.

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