How long do leftovers really last? And other holiday food safety questions, answered

For many, the holiday season means tucking into big meals with friends and family who gather to celebrate.

But once the dinner ends, attention turns to packing away leftovers.

Every year, one in eight Canadians — about four million — are affected by a food-borne illness. Of these, there are 11,600 hospitalizations and more than 230 deaths, the Public Health Agency of Canada estimated.

The prospect of leftovers can stir debate: How long does cooked food last for? Will old pasta really kill you? And do you really need to throw out hard cheese that's started to grow mould, or is it fine to just cut those bits off and eat the rest?

To save you the hassle — and the fight — CBC News put those questions and more to Canadian food scientists. Here's what they said.

Lawrence Goodridge, a food safety professor at the University of Guelph, said it's not a good idea to leave food out at room temperature.

"There's what's called the danger zone, which is between 4 C and 60 C," Goodridge said in an interview. "This is where bacteria will grow very happily."

The kitchen advice to "keep hot food hot and cold foods cold" is based on this temperature range.

As for why, microbiologists point to a bacterial species called Bacillus cereus, which can produce spores that survive being cooked.

Jennifer Ronholm, an associate professor at McGill University, said that bacteria produces a heat-stable toxin called cereulide that can cause serious illness.

"If you ingest small amounts of cereulide, you can get vomiting, liver failure, respiratory distress, or even damaged muscle tissues releasing proteins and electrolytes into your blood and these can damage your heart and kidneys," said Ronholm, who also holds the Canada Research Chair in Agricultural Microbiology.

Deaths from cereulide are extremely rare, Ronholm said. However, she pointed to a 2011 lethal case report of a 20-year-old man in Brussels, Belgium, associated with eating pasta contaminated with Bacillus cereus.

The pasta had been prepared five days before and left in the kitchen at room temperature that whole time, researchers said. Before his death, four fatal cases attributed to cereulide had been reported, they said.

Anything you can do to get a pot of food out of that danger zone as soon as you safely can is important, Ronholm said.