"A lot of people rely on the sniff test, [but] that means nothing whatsoever," says Lydia Buchtmann from the Food Safety Information Council.
Food can look, smell and taste just fine but still contain enough food poisoning bacteria to make you very sick, Ms Buchtmann says.
On the other hand, if food smells off, you're right in thinking it's a good idea not to eat it.
When a plate of leftovers starts to pong, it means spoilage bacteria have taken hold.
When spoilage bugs are at work, it's the start of the rotting process by which food decomposes, Ms Buchtmann says.
These bacteria generally cause an undesirable change in the composition of food.
They can make meats slimy and turn milk or yoghurt lumpy for example.
Foods affected this way will almost certainly not taste good.
While spoilage bugs are different from the microbes that cause food poisoning, if conditions are right for spoilage bugs, there's a good chance the food poisoning bugs have grown too.
That means you may well be risking a nasty bout of stomach cramps, diarrhoea, and vomiting that could see you laid low for days.
So the nose test is right in that if it stinks, it's best to toss it out. But never assume that just because it smells fine, it's fine to eat.
How long can leftovers be kept?
So how can you know if leftovers are safe to eat? Unfortunately, there are no iron-clad guarantees, Ms Buchtmann says.
Labelling your parcel of goodies with the date before you stow them in the fridge is a good start.
Food poisoning: An alphabetical guide to the bugs that cause it
Here are some of the culprits responsible for food poisoning.
Most leftovers should keep two to three days in a fridge maintained at the right temperature (5 degrees Celsius).
If you don't think they'll be eaten in that time, consider freezing them.
Be aware that cooked rice and pasta are best kept no more than two to three days too.
These are high-risk foods because they can contain spores of a food poisoning bacteria called Bacillus cereus.
The spores can survive the cooking process and produce new bacteria that can multiply while the rice or pasta is still warm.
The longer cooked rice or pasta are left at room temperature, the more likely it is that the bacteria (or toxins they produce) could make the food unsafe to eat.
Ideally, you want to refrigerate cooked rice and pasta as soon as it stops steaming, or within an hour.
The bacteria will still grow in the fridge, just more slowly, so don't be tempted to extend the two to three day limit, Ms Buchtmann advises.
Bulk cooking risk
If your leftovers are from bulk cooked "winter warmers" such as soups, casseroles and stews, be extra careful.
Handling large amounts of food imposes extra risk.
If the food is left to cool slowly, it increases the chance food poisoning bacteria can grow and produce dangerous toxins that won't be destroyed by further cooking, Ms Buchtmann says.
"The main thing to remember is to divide any food that you aren't going to eat immediately into small portions about the size of a takeaway container.
"Do this as soon as the food has stopped steaming and refrigerate or freeze straight away. The food will cool quickest in small containers, reducing the risk."
When reheating food, make sure it is hot all the way through.
If you use a slow cooker, make sure it keeps the food at a safe holding temperature of 60 degrees Celsius or above until you are ready to eat it.
Leftovers left out REMEMBER: 2hour/4hour rule
Other high-risk leftovers are those that have been left out of the fridge for periods longer than an hour.
The "danger zone" is 5-60 degrees Celsius and most food left in this zone for up to two hours should be safe to refrigerate.
But if it's been sitting out for two to four hours, you should either eat it immediately or dispose of it.
Anything that's out over four hours is best thrown away.
Source: ABC News