Should you smell food before throwing it away?
Half of the world's food is wasted, a new report says. Consumers typically use the "best-before" or "use-by" dates to decide when to throw food away. But should the "sniff test" be used instead?
Sour milk. Smelly fish. A mouldy banana.
Some foods have a distinct smell when they are past their best.
Typically, people rely on "best-before" dates and "use-by" labels to determine when to throw away food.
Guidance from the UK's Food Standards Agency says "best-before" dates are supposed to tell the consumer more about "quality than safety" - indicating when a product may begin to lose its flavour and texture, but not that the product becomes dangerous to eat.
Eggs are an exception. The advice is they should be eaten by a day or two after the "best-before" date, providing the eggs are cooked thoroughly until yolk and white are both solid, or if they are used in dishes where they will be fully cooked, such as a cake.
The quality of an egg deteriorates, and if any salmonella bacteria are present, they could make you ill.
"Use-by" dates apply to food that goes off quickly, such as meat products, which may put health at risk if eaten after a certain time period.
But would the "sniff test" help reduce food waste?
Although strong, "rank" smells are a clear indicator that food - especially meat - should be thrown away, the reality is people won't be able to tell if food is definitely safe to eat from smelling it, according to food expert Stefan Gates.
"The trouble is that a smaller, but still dangerous, concentration of pathogens won't necessarily be detectable by smell.
"And remember that there are good bacteria, especially in yoghurt and cheeses, and bad bacteria like E.Coli, salmonella, botulism and various clostridium bacteria.
"Researchers who work with these bacteria say that the smell of some of these is distinctive, but only at certain concentrations, and possibly in combination with other factors," he says.
Gates advocates using "use-by" dates, particularly for meat. But he says they are less useful for vegetables, which often carry less harmful bacteria.
If people, especially children, cooked more - so they were more connected to their food and how it works - they would also care more about food, and be better equipped to waste less, he says.
Chris Smith, a professor of food science at Manchester Food Research Centre, agrees education is key.
He says part of the reason consumers have become so dependent upon "use-by" dates is that they are no longer able to recognise when food is inedible.
"In the 1960s, people would go to a butcher and smell meat to see how fresh it was. The best beef would be hung for 21-28 days before it was eaten. Nowadays so much is pre-packaged, people don't have the same experience of smelling food.
"Until we regain an understanding of the smells that indicate inedibility, we have to rely on the systems which do work, like use-by dates," he says.
For example, to check pre-packaged meat is safe to eat by smelling it, the package needs to be opened, and kept at room temperature for 30 minutes, he argues.
But he says although smelling food can be helpful in some situations, in others it isn't that simple.
"'Smelly' cheeses such as Stinking Bishop don't go off by smell. And in some cases the food is only eaten once the decay has begun." Many people choose to "hang" pheasants for several days before eating them.
In other instances, the smell test is just not that effective.
"Bread will become mouldy before it begins to smell hence visual inspection is best," he says.
So the sniff-test might be an extra indicator for a few cooking connoisseurs, but the ultimate safe advice is stick to the "use-by" date.