Within four hours of devouring a second helping of my home-cooked Ottolenghi recipe for tuna and cheese pasta bake, my creation was rapidly evacuating my body.
I’d batch-cooked three servings of the dish two weeks earlier and stored it in the freezer. Then, after thawing a portion in the fridge for a day, reheating in the microwave for three minutes and eating, the night was peppered with exhausting trips to the loo and the following day fatigue pinned me to the sofa.
The vomiting, diarrhoea and tiredness all pointed to a classic case of food poisoning — but Ottolenghi’s recipe was hardly in the dock, seeing as the first serving I’d had a fortnight earlier was perfectly delicious.
No, it must have been something I’d done with the dish since. Welcome to the food poisoning perils of batch-cooking.
As our shopping budgets are squeezed by rising prices, more of us will be making our money go further by cooking big, economical pots of food to store and use later.
But there are rules to the process.
Within four hours of devouring a second helping of my home-cooked Ottolenghi recipe for tuna and cheese pasta bake, my creation was rapidly evacuating my body
Dr Matthew Gilmour, a microbiologist at the Quadram Institute (formerly the Institute of Food Research), based in Norwich, says tuna, cheese and pasta are all fine to freeze and reheat; what was at fault, he says, was my timing.
Dr Gilmour surmises that I’d left the oven dish on the kichen counter for too long before batching it up into a plastic tub and freezing it. I’d left it cooling and resting at room temperature for three hours — and that had allowed the bacteria in the dish to multiply to harmful levels.
‘After food is cooked and cooled down, package it up and get it in the freezer as quickly as possible — within two hours,’ says Dr Gilmour. He recommends covering it with foil while it cools, preventing cross-contamination from, say, a fly.
You should also transfer the food to a new dish, says Sylvia Anderson, a food hygiene consultant based in Wimbledon, South London, as leaving it in a hot dish means it takes longer to cool down, allowing time for any bacteria present to grow.
I was unaware of such rules — and I’m not the only one, it seems.
Last year, there were 4,369 recorded cases of food poisoning in England and Wales, according to the UK Health Security Agency, but most cases go unreported. A study in 2018 by the Food Standards Agency estimated that there are in fact 2.4 million cases per year.
And the trend for batch-cooking may well push that figure higher.
Sylvia Anderson says: ‘I’m amazed when I see people on Instagram [the social media platform] placing five-day batch-cooked portions in the fridge.
As our shopping budgets are squeezed by rising prices, more of us will be making our money go further by cooking big, economical pots of food to store and use later. But there are rules to the process
‘In the hospitality industry, pre-cooked food is kept in the fridge for only three days. After that it becomes unsafe — so it’s best to freeze the other two portions.’
Another key mistake that people make is to store things in the freezer for too long, she says. ‘In the industry, we say pre-prepared meals should be frozen for no more than a month.’
Sylvia suggests labelling foods with a date to keep tabs on how long they’ve been in the freezer.
Nor should you assume that freezing kills bugs, Dr Gilmour warns. Microbes are merely dormant and reanimate once thawed. This means you should also take care when defrosting food from your freezer.
‘If you leave something on the side to defrost at room temperature, there’s an increased risk that microbes will multiply,’ says Dr Gilmour. ‘But most organisms can’t grow below 4c — the temperature in your fridge.’
Microwave defrosting can speed up the process, but stir the dish halfway through so that it’s not just hot on the outside. Once it’s safely defrosted, reheat in the oven or microwave, but ensure the dish is piping hot all the way through.
Frozen raw meat should never be defrosted in the microwave, though, as the raised temperature can encourage bacteria growth — it’s best left to thaw slowly in the fridge. And don’t be tempted to run the meat under warm water as any microbes present could contaminate the sink and nearby utensils.
There is a long list of organisms that can cause food poisoning, says Dr Gilmour, ‘but the three most likely in the UK are salmonella, campylobacter and listeria’.
These are bacteria that can be found in soil and water, which means animals feeding off the land are potential sources of contamination, as are vegetables grown in the soil or fertilised by the manure of infected animals.
Norovirus (known as the winter vomiting bug) is another common cause of food-related sickness. But this is a virus rather than bacterium, so it won’t multiply in food. ‘A virus needs to infect a living human or animal cell to multiply,’ Dr Gilmour says.
Norovirus, however, contaminates dishes from faecal spores on the hands of an infected person, so it’s important to wash hands before preparing meals.
Microbes that get through the gastrointestinal tract attach to the lining of your gut to survive. ‘This disrupts the ecosystem between the vast number of healthy bacteria in your gut,’ says Dr Gilmour — and your body tries to eject the ‘bad’ bacteria by vomiting.
The vomiting, diarrhoea and tiredness all pointed to a classic case of food poisoning — but Ottolenghi’s recipe was hardly in the dock, seeing as the first serving I’d had a fortnight earlier was perfectly delicious
‘But diarrhoea can sometimes be a survival strategy of the organism — a means to escape and infect others,’ he adds.
Serious illness from food is rare, but the most vulnerable are the very old, the very young or people undergoing treatment for other conditions, such as cancer.
However, listeria (found in soft cheese or contaminated meat, for example) can travel to the brain to cause meningitis — an infection of the protective tissues (or meninges) around the brain and spinal cord. Listeria can cross the placenta of a pregnant woman, too, infecting the foetus.
A campylobacter infection (often associated with under-cooked chicken) can, in rare cases, lead to Guillain-Barré syndrome — a disorder in which the immune system attacks the nerves, causing severe movement issues in the limbs.
A friend of mine had this after a bout of food poisoning, possibly from a supermarket-bought oven-cook chicken meal. He endured a week of frightening, bed-bound paralysis, and then two years of mental stress, fatigue and physiotherapy to improve the restricted movement in his hands and feet.
Dr Gilmour says: ‘Cases like this are rare, but unfortunately it can take years to recover.’
Of course, most food-borne infections incur only mild symptoms of vomiting, diarrhoea and fatigue. NHS advice is to rest and keep hydrated, but to avoid sweetened drinks as bacteria can feed off the high sugar content.
Prevention is always better than cure, though, and one food to be especially careful of reheating is rice, which is home to bacillus cereus, a toxin-producing bacteria.
Takeaway rice could already have been reheated once in the restaurant. ‘The rule in our house is never cook, freeze or reheat food more than once,’ says Dr Gilmour.
And be warned that a simple salad can harbour bacteria, too.
‘I wouldn’t eat anything from my garden without washing it first,’ says Sylvia Anderson, ‘given the potential contamination from bacteria found in soil, animal poo, dirt and worms.’
She recommends giving salads a ‘bath’ in a mixing bowl of water with a teaspoon of salt to help destroy any bacteria present.
After 15 minutes, she says, the leaves will rise to the surface, leaving the debris at the bottom.
While my illness was unpleasant, I know from my friend who was struck down for a week with Guillain-Barré syndrome that it could have been much, much worse.
But at least now I know how to batch-cook safely.
The surprising causes of head pain. This week: Stripes
Striped patterns and shapes — such as those found in radiators — may trigger activity in the brain that can be responsible for causing a migraine attack.
This is especially true if you’re sensitive to light, according to studies by the University Medical Centre Utrecht, in the Netherlands, and New York University. Researchers believe stripey patterns set off a sequence of nerve activity in the brain known as gamma oscillations.
‘Essentially, striped patterns can, in some people, lead to an overreaction in the brain,’ says Dr Andy Dowson, a headache specialist at King’s College Hospital in London. This would then cause a migraine that may last for several hours or more.