Earth First

Shelf Life & Food Waste | The Science & Tech Behind Shelf Life

Whether we’re in a supermarket or digging through the contents of our own fridge to make dinner, most of us make decisions about what to buy, cook, or eat by looking at the “use by” or “best before” dates on our food. But what actually determines a food’s shelf life?

What is shelf-life?

Put simply, a food’s shelf life is how long it will last before it goes bad, loses nutritional value, or becomes unsafe to eat. Lots of different factors come into play – from whether it’s been processed to how it’s stored.1

For fruit and vegetables, how ripe they were when they were harvested makes a big difference to how long they’ll last on a shelf.2 Many fruits are picked before they’re ripe and then ripened artificially to ensure they will reach supermarkets in good condition.

How we stop food waste

There are microorganisms – like bacteria, yeast, and mould – around us, and on our food, all the time. Food spoils when a subset of microorganisms that can cause disease are allowed to grow in large enough numbers.

These microorganisms tend to grow rapidly at room temperature, but at fridge and freezer temperatures, their growth is slowed. Humans have also come up with a variety of processing methods – drying or canning beans, pickling and preserving fruits and vegetables – that can prevent these microorganisms from thriving.

‘Use by’ vs ‘best before’

When it comes to deciding whether food we’ve made ourselves at home is still good to eat, most of us trust our own judgement – and with things like milk, we can recognise the pungent smell when it has gone off immediately. But at the supermarket, we get a helping hand in the form of “use by” or “best before” dates on everything from loaves of bread to bags of pre-washed salad.

What a lot of people don’t realise is that there’s a big difference between those two terms: “use by” means that the food may not be safe to eat after that date, but “best before” tells you when the quality of the food will start to deteriorate. EU legislation says that most pre-packed foods need a date mark, and foods that are highly perishable, like yoghurt or unpasteurised fruit juices, need a “use by” date rather than a “best before” one.3

Up to 10% of the annual food waste in the EU is linked to dates on the food’s packaging.3 And while “use by” dates provide essential information to keep us from getting ill, labelling food with dates can be misinterpreted by consumers – so scientists are looking into more accurate ways to determine whether or not food is still good to eat.

New tech: better shelf-life estimates

There’s already a lot of science that goes into working out how long prepared food will last. One method is to test in the lab how microbes grow in particular environments and use this to predict whether they’ll survive (or not) during food production, transportation, and storage.4

But now researchers are taking that a step further to provide real-time information on whether food is safe to eat. For example, scientists are developing sensors that can detect noxious gases given off by fish and meat as it goes off.5 The idea is that by reading a sensor on the package with your smartphone, you’d no longer have to rely on a labelled date (or your own nose!) to make your decision – preventing people from throwing away food that is still perfectly fine and helping to cut food waste.

Other researchers are looking into using acoustic waves to measure the firmness of individual tropical fruits like avocados and mangoes to determine if they are ripe enough to be sold, rather than relying on destructive testing methods – like extracting a sample – on just one from a larger batch.6

Can technology extend shelf-life?

Other research focuses on extending shelf life rather than just providing a more accurate estimate.

Some researchers today are working on creating new types of packaging to keep our foods fresher for longer – like films that inhibit the growth of microbes which could help bread stay fresh in its packaging longer, or coatings put on the outsides of avocados which could keep avocados ripe for longer before they turn into the dreaded brown mush.7,8

Of course, there is one technology that has been extending the shelf life of food for several decades already: plastic. Wrapping a cucumber in just a small amount of plastic film can lengthen its shelf life from 3 to 14 days.9 This is one of the challenges that comes with the zero-waste movement and something producers and supermarkets have to think about when switching to plastic-free packaging.

Editor's Note: Since this article was first published, progress has been made around best-before dates. For example, many supermarkets have been scrapping best-before dates on fresh products like vegetables in recent years. Keep an eye out for the latest developments!

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