Step-By-Step Guide: When should you throw away leftovers?

Refrigeration is the most important invention in the history of food. But while refrigerators have only been used for the past 100 years or so, people have long used cool natural environments to store foods for extended periods.

Temperature is important for controlling microbial growth. Just as we find food wholesome, bacteria and fungi also enjoy the nutritional benefits of foods. They will consume the food and multiply, eventually “spoiling” the food.

If the microbe can cause disease – such as salmonella, campylobacter, E coli or listeria – you’re at risk of food poisoning.

How to stop bugs growing in our food

All forms of life require a few basic things to grow: a source of energy, oxygen (for higher forms of life), water and simple chemical building blocks that provide nitrogen, phosphorous and sulphur – and the correct temperature. Water is key, and denying it severely restricts microbial growth.

That’s why salt has long been used as a preservative for perishable foods like meats; salt binds the water and makes it unavailable to microbes..

Of course, cooking kills the microbes of concern, but they can contaminate and grow in the food afterwards.

If the food can’t be salted or pickled, or you have leftovers of cooked food, you’ll need to store the food at a temperature microbes don’t like. Refrigeration is the most effective option.

How to store food safely

The “danger zone” is the temperature range between 5C and 60C, where most common food poisoning bacteria like to grow. To avoid the danger zone, keep hot foods above 60C and store foods below 5C.

The two-hour/four-hour guidelines can also help avoid food poisoning from leftovers:

- less than two hours, use it immediately or store it appropriately

- two to four hours, use it immediately

- longer than four hours, discard it

So, if the food has been sitting on the table after a long lunch on a warm day, it’s probably best to discard.

If the food is OK, store it in small portions.

Using some common sense, and understanding how microbes grow, can help avoid a nasty case of diarrhoea – or worse.


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