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Within four hours of devouring a second batch of my homemade Ottolenghi tuna cheese pasta casserole recipe, my creation quickly evacuated my body.
I had cooked three batches of the dish two weeks earlier and stored them in the freezer. After defrosting a portion in the fridge for a day, warming it up in the microwave for three minutes and eating it, the night was filled with strenuous trips to the toilet and the next day I was tied to the sofa by fatigue.
The vomiting, diarrhea and fatigue all pointed to a classic case of food poisoning - but Ottolenghi's recipe was hardly in the dock, as the first batch I had a fortnight earlier was absolutely delicious.
No, it must have been something I had done to the dish since then. Welcome to the Dangers of Food Poisoning in Batch Cooking.
As our shopping budgets are squeezed by rising prices, more of us will continue to spend our money by cooking large, economical pots of food to store and use later.
But there are rules to the process.
Within four hours of devouring a second batch of my homemade Ottolenghi tuna cheese pasta casserole recipe, my creation quickly evacuated my body
Dr. Matthew Gilmour, a microbiologist at the Norwich-based Quadram Institute (formerly the Institute of Food Research), says tuna, cheese and pasta freeze and reheat well; What was to blame, he says, was my timing.
Dr. Gilmour suspects I left the casserole dish on the kitchen counter too long before transferring it to Tupperware and freezing it. I had let it cool and sit at room temperature for three hours - and that had allowed the bacteria in the dish to multiply to harmful levels.
“After the food is cooked and cooled, package it and put it in the freezer as quickly as possible—within two hours,” says Dr. Gilmour. He recommends covering it with foil while it cools to prevent cross-contamination from, say, a fly.
You should also transfer the food to a new bowl, says Sylvia Anderson, a food hygiene consultant in Wimbledon, south London, as leaving it in a hot bowl takes longer to cool, allowing existing bacteria to grow.
I wasn't aware of these rules - and apparently I'm not the only one.
Last year, there were 4,369 recorded cases of food poisoning in England and Wales, according to the U.K. Health Security Agency, but most cases go unreported. A 2018 study by the Food Standards Agency estimates that there are actually 2.4 million cases per year.
And the trend toward batch cooking could well drive that number even higher.
Sylvia Anderson says: “I'm amazed when I see people on Instagram [the social media platform] putting five-day cooked portions in the fridge.
As our shopping budgets are squeezed by rising prices, more of us will continue to spend our money by cooking large, economical pots of food to store and use later. But there are rules to the process
"In the hospitality industry, pre-cooked food is only kept in the fridge for three days. After that it becomes unsafe - so it's best to freeze the other two portions."
Another major mistake people make is keeping things in the freezer for too long, she says. “In the industry we say prepared foods should not be frozen for longer than a month.”
Sylvia suggests putting a date on foods to keep track of how long they've been in the freezer.
You also shouldn't assume that freezing will kill insects, warns Dr. Gilmour. Microbes are merely inactive and are revived after thawing. Be careful when defrosting food from your freezer.
“If you leave something out at room temperature to thaw, there is an increased risk of microbes multiplying,” says Dr. Gilmour. “But most organisms can’t grow below 4°C – the temperature in your fridge.”
Defrosting in the microwave can speed up the process, but stir the dish halfway through so it's not just hot on the outside. Once safely thawed, reheat in the oven or microwave, but make sure the dish is hot throughout.
However, frozen raw meat should never be defrosted in the microwave as the elevated temperature can promote bacterial growth - it is best to defrost slowly in the refrigerator. 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 found in soil and water, meaning animals that feed on the land are potential sources of contamination, as are vegetables grown in soil or fertilized by the manure of infected animals.
Norovirus (known as winter vomiting) is another common cause of foodborne illness. But this is a virus rather than a bacteria, so it won't reproduce in food. “A virus must infect a living human or animal cell in order to reproduce,” says Dr. Gilmour.
However, norovirus contaminates dishes through fecal spores on the hands of an infected person, so it is important to wash your hands before preparing meals.
Microbes that pass through the gastrointestinal tract attach to the intestinal lining in order to survive. “This disrupts the ecosystem between the large number of healthy bacteria in your gut,” says Dr. Gilmour – and your body tries to expel the “bad” bacteria by vomiting.
The vomiting, diarrhea and fatigue all pointed to a classic case of food poisoning - but Ottolenghi's recipe was hardly in the dock, as the first batch I had a fortnight earlier was absolutely delicious
“But diarrhea can sometimes be a survival strategy for the organism – a way 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 those undergoing treatment for other illnesses such as cancer.
However, Listeria (found in soft cheese or contaminated meat, for example) can enter the brain and cause meningitis - an infection of the protective tissue (or meninges) around the brain and spinal cord. Listeria can also cross a pregnant woman's placenta and infect the fetus.
A Campylobacter infection (often associated with undercooked chicken) can, in rare cases, lead to Guillain-Barré syndrome - a condition in which the immune system attacks the nerves and causes severe movement problems in the limbs.
A friend of mine had this after getting food poisoning, possibly from an oven-baked chicken dish he bought at the supermarket. He endured a week of frightening bed-bound paralysis and then two years of psychological stress, fatigue and physical therapy to improve limited movement in his hands and feet.
Dr. Gilmour says: "Cases like this are rare, but unfortunately they can take years to recover from."
Of course, most foodborne infections only cause mild symptoms such as vomiting, diarrhea and fatigue. NHS advice is to rest and stay hydrated but avoid sweetened drinks as bacteria can feed on the high sugar levels.
However, prevention is always better than cure, and one food to be particularly careful with is rice, which is home to Bacillus cereus, a toxin-producing bacteria.
Takeaway rice could have been warmed up in the restaurant. “Our rule at home is never to cook, freeze or reheat food more than once,” says Dr. Gilmour.
And be warned that even a simple salad can harbor bacteria.
"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 feces, dirt and worms."
She recommends “bathing” salads in a mixing bowl with water and a teaspoon of salt to destroy any bacteria present.
After 15 minutes, she says, the leaves will rise to the surface, leaving debris on the ground.
Although my illness was unpleasant, I know from my friend who suffered from Guillain-Barré syndrome for a week that it could have been much, much worse.
But at least now I know how to batch cook safely.