Foods that stay edible for years

Archaeologists have found 3,000-year-old honey in Egyptian tombs that were perfectly edible. This is because honey is low in water content and high in sugar, and bacteria cannot thrive in it.
Archaeologists have found 3,000-year-old honey in Egyptian tombs that were perfectly edible. This is because honey is low in water content and high in sugar, and bacteria cannot thrive in it.PHOTO: REUTERS

Apart from Captain Robert Scott's fruitcake, here are other foods with a very long shelf life

News that, after 106 years, the British explorer Captain Robert Scott's fruitcake was found by the Antarctic Heritage Trust and "smelled edible", raises the question - are there other foods that have similar staying power?

The answer is yes.

HONEY

In 2015, archaeologists reported that while excavating tombs in Egypt, they had found 3,000-year- old honey and it was perfectly edible.

This durability is due to the unique features of honey. As it is low in water content and high in sugar, bacteria cannot thrive in it.

Honey also contains small amounts of hydrogen peroxide, which inhibits the growth of microbes. This is partly why bees produce it for the young - it is both food and protection.

Processing honey also helps as the sugars in honey are hygroscopic and tend to draw in atmos- pheric water, which is not ideal.

However, during processing and packaging, the heat treatment first removes water and then airtight lids keep the water out, helping it keep for a longer time.

Honey can go cloudy and crystallise when opened, as the sugars draw in water again, but this physical change can be reversed by simply warming the honey.

DRIED PULSES

As with honey, the key to a long shelf life is processing and storage.

Drying pulses increases the pulses' sugar concentration and lowers the water content, which makes it hard for bacteria and moulds to grow on them.

Also, any enzymes that would naturally break down the product after harvest are put into suspended animation.

If the container is airtight, the dried pulses will last for years and still be a great source of protein.

However, if you allow water in, they will last only a few months.

SOYA SAUCE

Soya sauce has the potential to last at least three years.

The combination of its salt content and being fermented means that, if it is unopened, it should have a very long shelf life.

How long it will last depends on the type of soya sauce and, when opened, the temperature it is stored at. If it does go off, it is likely to be due to mould growing around the lid.

VINEGAR

Some may argue that vinegar is, in fact, already spoiled wine or cider.

But its acidic nature, traditionally achieved using Acetobacter bacteria to ferment it, means other bacteria struggle to grow in it, and so it can last a very long time.

While white vinegar will remain almost unchanged indefinitely, other vinegars may change colour or produce a sediment.

Typically, this will not affect the safety of the product, but only the appearance and, perhaps, the flavour.

WHITE RICE

White rice has been eaten after being stored for 30 years in tins, with the parboiled rice passing a tasting-panel test.

What appears to be key for rice is atmosphere and temperature.

Studies have reported that a low temperature and a lack of oxygen appear to be important for its longevity.

Brown rice, although often considered to be healthier, has a shorter shelf life. Its fibrous bran contains unsaturated fats, which can turn rancid. So if your brown rice is oily and smells like old paint, it is best to throw it away.

DARK CHOCOLATE

There is some debate about whether chocolate goes bad. The addition of milk to chocolate may reduce its shelf life.

But dark chocolate appears to last better, despite not always looking like it has been.

This could be because, if it is not stored at a constant temperature, the fat can rise to the surface, leaving a bloom that looks a bit like mould.

If stored at a constant temperature, however, chocolate can last for two years or more, with concentrations of the compounds which some link to health benefits remaining throughout this time.

For most people, though, chocolate does not tend to last this long before it is eaten.

SUGAR AND SALT

Many of the foods that last for a long time are high in sugar and salt.

In simple terms, they draw water out, so if bacteria try to grow on the food, they will simply shrivel up. This is why we use salt to make ham, sugar to make jam, and both to make gravlax.

As foods in their own right, if salt and sugar are stored away from moisture in airtight containers, they will last indefinitely.

But additives, such as iodine added to salt, can reduce its shelf life to about five years.

Of course, most foods don't last very long.

This is because they contain the things microbes love, such as nutrients and water, and not much of the stuff they don't love, such as salt and acid.

Be aware that use-by dates are generally used for food safety reasons and best-before dates are more to do with the quality of the product.

The best-before date might have little bearing on the shelf life of some products, only how they look or taste.

•The authors are Coventry University's senior lecturer Duane Mellor, assistant lecturer Daniel Amund and senior lecturer in human nutrition Isabella Nyambayo

•This article first appeared in theconversation.com, a website of analyses from researchers

A version of this article appeared in the print edition of The Straits Times on August 22, 2017, with the headline 'Foods that stay edible for years'. Print Edition | Subscribe