How long will holiday leftovers keep?

You planned a massive Christmas feast with all the requisite trimmings and side dishes. But once dinner's over and you can't eat another bite, how long will the leftovers last?

The answer depends largely on how you store them and whether you've prepared them properly in the first place.

It's impossible to tell when and whether your leftovers will make you ill, since the microbes that cause food-borne illnesses don't necessarily give off clear signs like a change of colour or odour, says Brita Ball, interim director of the Food Safety Network at the University of Guelph.

"Just because something is spoiled doesn't mean it's unsafe, and just because something is not spoiled does not mean that it is safe," she says.

Some moulds, for instance, might look and smell off-putting but are perfectly safe to eat, while a bacteria like salmonella won't cause food to spoil, but can make you sick, she explains.

Moreover, even if you've killed off illness-causing bacteria during the cooking process, their spores may linger and germinate in leftovers, producing toxins that can't be destroyed by reheating or cooking again, Ms. Ball says.

Your best protection is to ensure you cook food to the appropriate temperatures, and that your hands, cooking surfaces and utensils are clean, and there's no cross-contamination of raw and cooked foods, she says.

Also, be sure to exercise the two-hour rule, she advises: Bacteria grow best between 4 degrees and 60 degrees Celsius, so food should not be left un-refrigerated for a total of more than two hours. That means if you've let your turkey sit out for an hour after you cook it, don't take it out of the fridge for more than an hour the next day, Ms. Ball says.

Rethinking 'best before' dates

Jonathan Maitland considers things like "best before" dates as mere recommendations, not rigid rules.

In a daring experiment in 2008, the British journalist tested the limits of food expiry dates for two weeks. He ate fuzzy, green bread that was more than three weeks past its prime; off-colour, grey minced steak that was seven days past its use-by date; and a chicken breast six days past its expiry. As he reported in The Daily Mail, he didn't experience so much as an upset stomach.

The experiment was part of his investigation into how much edible food people throw out. (In Britain, it's estimated that 6.7 million tonnes of safe-to-eat food winds up in the garbage every year.)

"It's verging on the morally obscene to throw away precious, wonderful food just because somebody stamped a date on it saying it might not be as good tomorrow as it is today," Mr. Maitland said by phone from England.

"I'm not advising people to go around eating horrible, foul-smelling, stale food. But if something's cooked and it's in the fridge and it's been cooked in accordance to all the guidelines, then you should be fine. It's a question of common sense."

Mr. Maitland recalls that his mother used to cook Christmas turkeys, weighing up to 42 pounds, for just the two of them, which would last them until late January. That's weeks beyond what the Canadian Partnership for Consumer Food Safety Education considers safe for a refrigerated, cooked turkey.

Even more extreme, Mr. Maitland says he once interviewed a woman who ate some cheese that had been made in the 1400s. ("She said it tasted very good," he says.)

So is there anything the man who devoured week-old, expired chicken won't eat?

"The moment something tasted off – whether it's milk or butter or whatever – it would be absolutely out the window," he says. "I certainly rely on my nose a lot, but beyond that, I have no limits.

Mr. Maitland's one piece of advice for dealing with Christmas leftovers is to splurge on a nice jar of caramelized onion chutney, which can be used to dress up turkey sandwiches, or served on the side of a reheated platter.

"Your turkey will come back from the dead like Lazarus. It will completely revitalize it. It will be born again," he says.

Then again, there's a simpler and less risky solution to make sure your leftovers don't go to waste: Prepare only as much food as you know you can eat.