It's a simple fact, undesirable pathogens on – or in – your food can make you ill.
Sometimes very ill.
And those pathogens are almost always bacteria or parasites.
It's also true that bacteria, or their toxins will, inevitably, end up on nearly every ingredient you use when you cook. And even boiling won't kill some of them.
So, to keep safe – and protect others - you need to achieve two objectives.
- Destroy any existing pathogens in – or on – your food
- Prevent any new pathogens from growing in – or on – your food
You can destroy most pathogens with heat. There are two ways to do it: at high temperatures instantly or low temperatures slowly.
High temperatures destroy pathogens instantly
At 74ºC all pathogens in food are destroyed instantly. Water boils at 100ºC, so that more than does the job.
Stocks, stews, casseroles and braises must always be heated right through to a minimum of 74ºC to destroy pathogens.
Note Food bourne Botulism can be deadly. Boiling for 10 minutes neutralises Botulism toxins. But – the truth is – you're ten times more likely to be killed by lightning than by food contaminated with botulism. (Between 1989 and 2005 there were three food borne Botulism deaths in the UK. Whereas, lightning kills an average of two people a year.)
Low temperatures destroy pathogens slowly
Pasteurisation does the same job as high heat or boiling – but at a lower temperature.
It's a function of time and temperature. The lower the temperature the slower your food will be pasteurised.
Bacteria stop reproducing and start to die between 55-74ºC. So pasteurisation can start at temperatures as low as 55ºC. See Are the pathogens in your meat - or on the meat?
Here are some examples of pasteurisation times versus temperature:
Beef – Lamb – Pork
Chicken – Turkey – Duck
Note Low temperature pasteurising can only be done if you hold food at a constant temperature and the meat is cooked through. You need a slow cooker that can be set in increments of one degree Centigrade.
How to prevent new pathogens growing in – or on – your food
Keep cooked – or perishable – food out of the Danger Zone.
Bacteria are one of the fastest reproducing organisms on the planet. They grow most rapidly in a temperature range between 4-60ºC, doubling in number every 4 to 20 minutes.
And that's why people call this temperature range the Danger Zone.
It means any cooked or perishable food should stay in the zone for no more than two hours without being re-pasteurised at 74ºC Any more than 4 hours and you need to bin it.
Room temperature is typically 20ºC – more or less in the middle of the Danger Zone. If the room temperature is above 32ºC (like a hot summer day) food should only be in the zone for 1 hour.
Get your food out of the Danger Zone as quickly as possible
Put stews, casseroles and braises in ice cold water to bring the temperature down – then put them in the fridge or freezer.
Alternatively, you can keep food at above 60ºC indefinitely without harmful pathogens growing.
Note If food is left out too long, some bacteria, such as staphylococcus aureus (staph), can form a heat-resistant toxin that cooking doesn't destroy. Ingesting these toxins will make you ill.
Your fridge is probably set to the wrong temperature
The average fridge in the UK is set to 7ºC which is far too warm.
In fact, it would be illegal if you were a catering business or food retailer. If you were to be a food retailer any perishable food held between 5ºC and 60ºC for 4 hours or more must be thrown away – by law. It stops people from getting ill – so you might as well apply the same rules at home.
The best temperature to set your fridge is between 2-3ºC. That way you can bring your food close to freezing, without getting it too cold.
A fridge thermometer will give you an accurate temperature reading. If you haven't got one already, you'd be wise to get one.
Freezing doesn't destroy all pathogens
Norovirus and some of the worst bacteria can survive freezing – freezing simply turns them dormant. When the food's thawed they're ready to start growing – and multiplying – again.
All moist cooked foods are susceptible to being recolonised by survivalist bacteria
Pasteurisation or boiling does destroy bacteria but not the spores they release – because spores can survive high temperatures.
So, when the temperature of whatever you've cooked drops below 55ºC, the spores germinate and begin to grow, multiply, and produce toxins.
What happens to a cooked casserole – or pot of stock – left at room temperature overnight?
By the morning your casserole or stock will be full of bacteria and need to be re-pasteurised. Your food will then be seasoned and flavoured with millions – or even billions – of dead bacteria and their inactivated toxins. Want to eat that?.
Here's how many bacteria could end up in your meal – hour by hour, at room temperature:
The most common pathogens in food
Campylobacter
Campylobacter is the most common cause of food poisoning in the UK.
Grows and multiplies between 30-47ºC
Optimum temperature 37-42ºC
Neutralised after a few minutes at between 55-60°C
Salmonella
Chicken is highly susceptible to Salmonella.
Grows and multiplies between 6-46ºC
Optimum temperature 37ºC
Neutralised instantly at 74ºC
Listeria
Grows and multiplies between 1.5ºC and 45ºC
Optimum temperature 30-37ºC
Neutralised instantly at 50ºC
Escherichia coli (E coli)
Grows and multiplies between 10-45°C
Optimum temperature 37°C
Neutralised instantly at 71ºC
Shigella
Grows and multiplies between 6-47ºC
Optimum temperature 37ºC
Neutralised instantly at 65ºC
Simple food safety rules – anyone can keep to
Clean
Wash hands and surfaces often
Separate
Separate raw meat from other foods
Cook
Cook to the right temperature
Chill
Refrigerate food promptly