Reheating food safely

Reheating food is a great way to reduce food waste. Food must be reheated safely.

When reheating food you must be mindful of the ‘danger zone’. This is between 5°C to 63°C. This is the range within which bacteria can grow rapidly. It is not good enough to simply warm food. Food must be reheated thoroughly until it is steaming hot all the way through. This is essential to kill any harmful bacteria that may have been introduced or grown since the food was cooked.

Safe Reheating

Reheating means cooking food again. Food must be reheated until it is steaming hot all the way through. This will be when the core temperature reaches at least 75°C for 30 seconds (or equivalent) (82°C in Scotland). Even if you are going to place hot food into hot-holding equipment you must ensure it is reheated thoroughly first.

What are the best reheating methods?

The reheating methods for foods vary, but the most common are:

• Microwave Ovens
• Ovens/ Grills
• Hob

Whichever method is used, the manufacturer’s instructions must be followed.

Microwave ovens

Microwave ovens are the most commonly used for reheating foods as they generally have the shortest reheating times. But as you are probably aware, microwaves do not heat food evenly. Due to this, cool pockets can remain giving bacteria a place to thrive. For this reason, it is best to choose foods that can be stirred, otherwise, you are relying on moving the food around to try to eliminate these pockets. Stirring and leaving the product to stand is part of the process of reheating food when using a microwave. This is to help ensure that the food is reheated to the same temperature all the way through.

Microwaving may not be the best method if the product you are reheating required a crispy texture, such as pizza. For this, you are better off using a normal oven or grill.

Ovens/ Grills

You should pre-heat ovens or grills to the original cooking instructions for the product or in accordance with the manufacturer’s instructions. The food should be placed on a baking sheet or grill pan and placed into the oven or grill until the required core temperature is reached and until the product is steaming hot all the way through.

Hob

Best used for reheating liquid products such as soup or sauces. You should place the food in a pan on medium heat until the required temperature has been reached and until the product is steaming hot.

Taking accurate temperatures is important, so let’s take a look at how to do this.

How to check food is properly reheated

When reheating food you can use visual checks to ensure it is steaming/ piping hot all the way through. Alternatively, the core temperature can be checked by inserting the tip of a clean digital probe or cooking thermometer into the centre or thickest part of the food. You should check that the core temperature reaches at least 75°C for 30 seconds (or equivalent) (82°C in Scotland).

The probe must be cleaned and disinfected before and after use so as not to introduce bacteria into the food. The easiest way to do this is to use food-safe probe wipes. These must comply with either BS EN1276 or BS EN 13697.

A food-safe disinfectant or sanitiser can also be used but it must be left on the probe for the correct contact time to ensure bacteria are reduced to a safe level.

It is also essential to check that the probe is working properly so you can rely on the readings. This is called calibration. The temperature probe should be calibrated regularly. A simple way to check a digital probe is in iced water and boiling water.

The correct temperature readings should be between:

• -1°C and 1°C in iced water
• 99°C and 101°C in boiling water

If the reading is outside of this range the probe should be replaced or returned to the manufacturer to be calibrated. It is good practice to keep a record of when you have calibrated the probe.

So how many times can I reheat the food?

Cooked food should only be reheated once. This is because the more times a food goes through the temperature danger zone (i.e. is heated and cooled) there is increased risk of bacteria growing to unsafe levels. If bacteria are not killed during reheating, this is likely to cause food poisoning.

With symptoms such as stomach cramps, diarrhoea, nausea, vomiting or even death I think we can all agree this is best avoided.

So you are convinced, only reheating food once is the safest option, but you need to be careful as certain types of food may catch you out!

Takeaways

Leftover food items from takeaways and restaurants are a common option for reheating. The reason is many restaurants prepare food in advance, so elements or perhaps all of that delicious meal have potentially already been reheated. Batch cooking of rice is a common practice in restaurants. Takeaway rice has likely been reheated. Reheating of takeaway food will depend on how it was produced in the first place. Reheating of takeaway foods should ideally be avoided as they pose an increased risk of food poisoning.

Rice

Rice is being singled out for a good reason, Bacillus cereus. Bacillus cereus is a bacteria found in uncooked rice and has a trick up its sleeve. It can form spores which are heat resistant.

A spore can be described as a protective coating formed by some bacteria to help them survive adverse conditions such as cooking, drying and chemicals.

Bacillus cereus spores form when cooked rice is left in the temperature danger zone for extended periods. It is important to keep cooked rice out of the danger zone (5°C to 63°C) to prevent spores from forming.

This means next time you need to cool rice make sure you do it as quickly as possible. Ideally within 60 minutes. The fastest method is to use clean cold running water. Then place the cooled rice in the fridge or freezer as quickly as possible before the spores can form. UK guidance is that cooked rice which is stored in the fridge should be used within 24 hours.

Summary

Reheating means cooking food again. Food must be reheated until it is steaming hot all the way through.

Bacillus cereus can form spores in rice left in the temperature danger zone for extended periods of time.

According to the Food Standards Agency, food should only be reheated once.

Foods should be cooled quickly and stored in the fridge or freezer. They should then be reheated thoroughly until they are steaming hot all the way through.

Reheating of takeaway food should ideally be avoided as some businesses may have already pre-cooked and reheated food items.