How fresh is the food on supermarket shelves?

We all know that eating fresh food is better for you, and there's nothing more tempting than a crisp, shiny apple or a loaf of newly-baked bread.

But did you know that some of those apples could be up to a year old?

See also: Healthy living on the cheap - seven inside secrets

See also: Hundreds of pounds of food binned by Tesco on Christmas Eve

Supermarkets need to keep a steady supply of staple groceries, whether or not a particular item is in season, and have a number of tricks to preserve foods far longer than you might expect.

We look at a few of the items on the shelves that may have been hanging around longer than you'd think.

Apples
In the past, canny householders would wrap apples in newspaper and store them in an outhouse, where they would last for several months. Now, producers take this a step further by keeping them in a high-carbon dioxide atmosphere. They are also often treated with a chemical called 1-methylcyclopropene, which also retards ripening; as a result, supermarket apples can often be as much as a year old.

Fish
Just because a piece of fish looks and smells fresh, it isn't necessarily freshly-caught. Check for a 'previously-frozen' sticker - if you find one, that piece of fish could be as much as two years old.

Meat
Meat lasts a long time if it's refrigerated - and if, say, it's New Zealand lamb it has a long journey before it hits our shelves. This means it could be as much as eight weeks old - although that won't do the flavour any harm.

Potatoes
We all know what happens to potatoes if we're careless about storage - they start to turn green and sprout. However, growers have a number of techniques to delay this process. The potatoes are frequently put through a temperature-changing process which has them first in a warm, humid environment and then in a cold one, after which they are treated with a chemical known as CIPC or chlorpropham. As a result, they can last unscathed for up to a year.

Salad
Anyone that grows their own salad knows how quickly it turns to slime in the fridge. To avoid this happening during transit, producers wash it in chlorine and store it in bags filled with a low-oxygen atmosphere. As a result, those bags of 'fresh' salad can often be as much as three weeks old.

Bread
Supermarkets love to sue the smell of fresh bread to tempt your appetite and encourage you to buy more. However, while their bread is, as advertised 'baked in-store', this doesn't necessarily mean it's fresh. It's generally produced from part-baked dough, which is supplied frozen and which can be up to a year old.