Dr Kim-Yen Phan-Thien from the Faculty of Science shares her expert advice on food safety and managing your leftovers to get the best out of them.
Every Christmas, it seems there is one guarantee. A table stacked with enough food to feed a herd and, despite our hasty promises after every festive feast to reign it in next year, like Groundhog Day, we do it all again. But with every overdone Christmas banquet comes perhaps the best part of the season – leftovers.
Somehow the cranberry seems sweeter, the pork crackle tastier, and the potatoes more moreish. However, it can also feel like an endless task getting through the food in fear of wasting anything – but how long can we *really* store leftovers after Christmas Day?
Dr Kim-Yen Phan-Thien from the University of Sydney’s Faculty of Science is a food safety expert who has shared the best rules and practices to embrace this festive season and enjoy leftovers without worrying about your health.
The way food is treated will impact its safety and longevity. As a result, there isn't one reliable rule to follow. But to ensure you’re getting the most longevity out of your leftovers, Dr Phan-Thien recommends temperature control technique.
“When you serve food, hot food should be kept hot, and cold foods should be kept cold. Food should be kept above 60 degrees Celsius or below five degrees, and in between five to 60 degrees is what we can think of as the danger zone,” she says. “This temperature range tends to promote microbial growth.”
Christmas lunch can be an hours-long marathon concluded by a food coma, but this isn’t great for your food, sitting on the table, vulnerable to the elements.
“It’s nice to have a great big spread, but if people leave food out for several hours, you shouldn’t keep that and eat the leftovers later,” Dr Phan-Thien says.
“If it’s spent four hours at ambient temperature, some pathogens will grow. So it’s better to manage your food by putting out smaller portions, keeping the rest stored appropriately in the fridge, and bringing out and replenishing as necessary.”
The food can sit on the table within a two-hour window, and if it's stored in the fridge in that time frame, it can be eaten as leftovers. While it depends on the food, it's usually safe to eat within the next two to three days, and it’s essential food that was hot is reheated well.
"A turkey roast is generally safe to eat when cooked properly as the treatment will kill any pathogens there. However, if you're going to store and eat the leftovers afterwards, you want to refrigerate or freeze them as quickly as possible,” Dr Phan-Thien explains.
"If it has been in the danger zone for more than two hours, you want to eat or refrigerate immediately. You shouldn't eat the leftovers if it's more than four hours."
The rate of cooling will make or break your leftovers, and your hardworking fridge can only keep everything fresh if its temperature is consistent. But with stacks of food piling on every shelf, that isn’t maintainable.
Dr Phan-Thien's solution is to avoid packing large quantities into one container. To avoid condensation inside the container, allow food to stop steaming before placing it inside.
Australians typically aren’t afraid of squelching hot Christmas Days. Barbecues are fired up, and aircons hard at work.
However, it’s not the best for the quality of our food, which may suffer from temperature abuse with a premature arrival to the danger zone.
“Be really conscious of temperature abuse and be prepared by having ice blocks available,” advises Dr Phan-Thien.
Food should be kept above 60 degrees Celsius or below five degrees, and in between five to 60 degrees is what we can think of as the danger zone.
“You can do things to increase the rate of cooling to help your food and your fridge out, like putting the food on ice for a bit to bring the temperature down before you stick it in the fridge.
“Instead of leaving your cooked food out on a plate, you can put them on ice as a part of the way you serve it so it can last a bit longer.”
A fly landing on a meal after hours of cooking is disappointing, and while some people are happy to turn a blind eye, others walk solemnly to the bin.
According to Dr Phan-Thien, the issue with flies is that they’re attracted to manure, which can contain organisms like Escherichia coli and Salmonella enterica.
“The issue if you have a fly land on your food is it potentially transfers some pathogens, aside from being a bit gross,” she said.
However, this doesn’t necessarily mean you have to throw away the food, but that varies from person to person.
“They may land on manure, pick up some bacteria, then land on your food and transfer it there, but if it’s lightly touched your food and flown away, then the amount of risk that you’ve got an infectious dose is not great,” says Dr Phan-Thien.
“However, if that food is left out at a temperature that supports microbial growth, those pathogens can multiply, and food safety risks increase.
“Also, remember, we need to be extra cautious when it comes to vulnerable people – the young, old, pregnant and immunocompromised – as these groups can become ill at a lower infectious dose.”
It’s not just our own health we’re worried about but also that of our four-legged companions. Dr Anne Quain from the University of Sydney’s School of Veterinary Science reported she sees numerous dogs after Christmas, suffering from vomiting and diarrhoea from eating treats and leftovers from the table.
She advises, "Most of those cases have involved dogs that have eaten either the Christmas ham, lamb or turkey – and we have seen some incidences as a result of prawns.
"Dogs often have a reasonably bland diet. A sudden influx of fatty festive foods can wreak havoc on their gut, leading to gastroenteritis, diarrhoea, or pancreatitis. They can also suffer from intestinal obstruction or perforation due to foreign bodies like bones, kebab sticks and toothpicks.”
As a rule of thumb, if your pet is unwell, please get them to your vet. Don’t delay, particularly if they have vomiting or diarrhoea and especially if they are not drinking. It could be a life-threatening condition, such as pancreatitis or gastric dilation (GVD).