By admin 
For many, the holidays mean eating large meals with friends and family gathering to celebrate.
But once dinner is over, the focus turns to packing up the leftovers.
Each year, one in eight Canadians – approximately four million – is affected by a foodborne illness (new window). Of these, 11,600 have been hospitalizations and more than 230 deaths, the Public Health Agency of Canada estimates.
The prospect of leftovers can spark debate: How long does cooked food last? Will Old Pasta Really Kill You? And should you really throw away hard cheese that starts to mold, or is it okay to just cut off those pieces and eat the rest?
To save you the hassle – and the struggle – CBC News put these questions and more to Canadian food scientists. This is what they said.
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Can I leave cooked food on the counter for a week as long as I reheat it every time I eat it?
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 is what is called the danger zone, which is between 4 and 60 degrees Celsius. Goodridge said in an interview. This is where bacteria will grow very happily.
The kitchen advice is to “keep hot dishes warm and cold dishes cold (new window)” is based on this temperature range.
Food safety experts recommend dividing soup into smaller containers for storage rather than in a large pot.
Photo: Getty Images / Dawid Jozwiak
As for why, microbiologists point to a species of bacteria called Bacillus cereus, which can produce spores that survive cooking.
Jennifer Ronholm, an associate professor at McGill University, said bacteria produce a heat-stable substance (new window)toxin (new window) called cereulide, which can cause serious illness.
If you take small amounts of cereulide, you may experience vomiting, liver failure, respiratory distress, or even damaged muscle tissue, which releases proteins and electrolytes into your blood. These can damage your heart and kidneys. said Ronholm, who also holds the Canada Research Chair in Agricultural Microbiology.
Cereulide deaths (new window) are extremely rare, Ronholm said. However, she pointed to a fatal 2011 case report of a 20-year-old man in Brussels, Belgium, who was linked to eating pasta contaminated with Bacillus cereus.
The pasta had been prepared five days earlier and kept in the kitchen at room temperature the entire time, researchers said. Before his death, four fatal cases attributed to cereulide had been reported, they said.
Do I need to cool a hot jar of food before putting it in the refrigerator?
Anything you can do to get a jar of food out of that danger zone as quickly as possible is important, Ronholm said.
Ronholm suggested leaving the pot on the counter until you no longer see steam, then putting it in the refrigerator.
Balance is the goal, says microbiologist Keith Warriner, professor of nutritional sciences at the University of Guelph. If a jar of food is too hot when placed in the refrigerator, the temperature of the refrigerator can rise into that danger zone and cause condensation, allowing microbial growth by pathogens such as Listeria.
However, modern refrigerators are more efficient at maintaining temperature and reducing condensation. he said.
Does the depth of the container matter when storing cooked food?
Yes, it matters, says Kaidi Wang, an assistant professor at the University of Saskatchewan who also holds the Agriculture and Agri-Food Innovation Chair in Applied Microbiology.
Deep containers tend to retain heat longer, which increases the risk of bacterial growth. Wang said.
Shallow containers (new window) allows food to cool faster, reducing time in the danger zone.
And smaller amounts of food cool faster than larger ones, Warriner said.
Time can be an important factor for some dangerous bacteria (new window)Warriner said. Clostridium perfringes (new window)which can cause an infection with symptoms such as diarrhea and cramps, one of the fastest growing bacteria known. Every nine minutes the bacteria can double in number.
It doesn’t take long before a dangerous level is reached.
Traces of (new window)Bacillus cereus (new window) can germinate and grow on food that is stored at temperatures between 8 C and 55 C for a sufficient period of time, according to the BC Center for Disease Control.
The bacteria are is a greater problem with high starch foods (rice and pasta) stored at room temperature and has been responsible for deaths, Warriner said.
Again, it comes down to how long the rice is kept in the danger temperature zone.
How long do leftovers actually last?
Food that has been left at room temperature for more than two hours should always be thrown away, says Ronholm.
That’s why it’s better to portion things out, Goodridge said, such as putting leftovers in the refrigerator or freezer.
LOOK | Food recalls in Canada in 2024:
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Are food recalls becoming more common in Canada?
A series of product recalls, including some involving E. coli, Listeria and salmonella, have raised food safety concerns. Lawrence Goodridge, director of the Canadian Research Institute for Food Safety at the University of Guelph, says the data does not indicate an increase in recalls, but adds that the pandemic has caused some disruptions to food safety.
A general rule is that leftovers should be consumed within five days of cooking. Week-old food may look and smell okay, but some pathogens, for example Listeria monocytogenes And Clostridium botulinumcan grow under cooling temperatures and become a hazard, Warriner said.
In addition to food safety, the University of British Columbia offers tips on reducing food waste (new window) during the holidays.
I have hard cheese that is just starting to mold. Can I just cut that off and eat the rest?
The texture of the cheese matters, say food scientists.
Goodridge said if the cheese is a hard cheese, there should be at least an inch of the cheese (new window) around and under the mold must be removed.
All other cheeses, soft and semi-hard, should be discarded if mold is present. said Goodridge. The same goes for other foods such as bread.
Ronholm said mold in hard cheese is a quality issue rather than a safety issue.
When we talk about cottage cheese, ricotta or cream cheese, that is not true. Ronholm said. With soft cheeses, the molds and toxins can penetrate better.
Do I need to reheat my leftovers to a certain temperature?
Ronholm, who said she owns four food thermometers, said yes.
Health Canada advises (new window): Heat leftovers to an internal temperature of 74 C and check this with a digital food thermometer. Soups, stews and gravies should be reheated to a boil.
Amin Zafar (new window) · CBC New