Use by dates, Food poisoning & Foodborne diseases

Use by dates, Food poisoning & Foodborne diseases

Estimated reading time: 9 minutes

So exactly what do the dates on your food mean? What is the meaning of a use by date? And why does bottled water have a use by date? In this blog post I’m looking at just what a “use by” date is and how it relates to food poisoning & foodborne diseases. I’ll also be looking onto exactly what the terms Food poisoning & Foodborne diseases actually mean.

If you look at canned foods you’ll find use by dates marked on them

Use by dates

If you’ve ever opened any food packaging before, you’ll have seen a date printed on the outside. For most dried foods, you’ll see that these dates are generally quite some time into the future. Whereas for fresh foods, the dates tend to be only a few days away.

But what do these dates really mean?

All foods sold in the UK and abroad have to be safe for you to eat & there are some pretty stringent laws in place to make sure that anyone who handles, makes, sells or gives away food, do so in a way that protects you, the consumer.

A lot of these laws have been incorporated into UK legislation from EU regulations, which is good because it means that the food you eat on holiday in the Mediterranean (for example) should be just as free from bacterial contamination as the food you eat in the UK. Now that the UK has left the EU, the UK legislation has been amended so that these laws and safety requirements will be staying in UK legislation. And that’s a good thing in my opinion.

As we’ve become all too aware over the last year or so, bacteria, viruses and fungi are all around us. Many of these microbes, as they’re known, happily spend their full life cycle (eat, excrete, multiply & die) on and in the food that we eat. While you may be repulsed at the idea of this, if you’ve ever eaten bread or cake, or had a glass of an alcoholic drink, you will have consumed yeast (fungi) and its waste products. And don’t forget all those expensive blue cheeses!

While many are deliberately introduced to foods to improve the flavour, or to create rise or alcohol, other types of bacteria are “spoilage bacteria”. Spoilage bacteria are microorganisms (microbes) that cause food to deteriorate and develop unpleasant odours, tastes, and textures.

But don’t forget, as humans we’re not alone. We are basically a walking colony of bacteria and mini-beasts, with many of these bacteria being essential to our survival & helping us to defend ourselves from microbes. For example without without the bacteria in our guts, our gut microbiome, we wouldn’t be able to digest our food properly.

So what does this all have to do with the dates on our food packaging?

As you now know, there are loads of different types of bacteria and viruses. For example some like to live on soft cheese, while others prefer to live on raw meat. As they multiply over time, there comes a point at which there are so many of them in and on the food that it wouldn’t be safe for us to eat. They’d simply overwhelm our defences and we’d suffer from a food borne illness, which is the term used to describe both, food poisoning & food borne disease.

People often use the term “food poisoning” to describe any gastric (stomach or intestine) related condition. Technically the terms “food poisoning” and “food borne disease” describe fundamentally different ways of becoming ill due to food contamination. But don’t worry, even food and health professionals sometimes use the terms food poisoning and foodborne disease incorrectly!

Food Poisoning

The term ‘food poisoning’ refers to consuming foods that contain a toxin or poison. Some toxins occur naturally in plants and animals (e.g. poisonous mushrooms or uncooked kidney beans), while others are released as a by-product of food poisoning bacteria living or dying.

When it comes to food poisoning, bacteria need to have multiplied to harmful levels (millions of bacteria) before you consume the contaminated food, for you to be affected. However, once they’re inside you, it’s the presence of the toxin from the bacteria, rather than the presence of the actual bacteria themselves, that leads to the illness.

The good news is that, provided the toxin is not present in sufficiently large enough concentration to damage your body’s organs, you can usually recover from food poisoning pretty quickly. The symptoms of food poisoning usually begin within one to two days of eating contaminated food, although they may start at any point between a few hours or weeks later.

Typical symptoms include:

  • feeling sick (nausea)
  • vomiting
  • diarrhoea, which may contain blood or mucus
  • stomach cramps & abdominal pain
  • a lack of energy and overall muscle weakness
  • loss of appetite
  • a high temperature (fever)
  • chills

In most cases, these symptoms pass in a few days and you will make a full recovery.

Foodborne Disease

Foodborne diseases operate in a fundamentally different way to food poisoning bacteria. Foodborne diseases represent a much greater threat to human life, potentially leading to long-term negative implications to health, with one taking up to 72 days before you become ill!

In foodborne disease, the food or water that you consume acts as a vehicle for the disease to enter the body. The toxin or viral multiplication then takes place within the body, where it spreads and remains for weeks or even months, potentially causing serious damage and even death.

Unlike most food poisoning bacteria, foodborne diseases only need a small number of organisms to enter the body to cause serious illness. One example of foodborne disease is Typhoid. Sadly this kills millions in developing countries through causing severe dehydration leading to organ failure.

Thankfully in the UK, the worst foodborne disease are rare. However, even those diseases normally found overseas can still pose a threat by being brought back into the UK by ‘carriers’; people who have contracted an illness through contaminated food or water.

So what does all this have to do with the dates on the packaging?

Well as you may have guessed, it’s all to do with the numbers of bacteria in/on the food that’s being manufactured and sold, and how many will have grown in/on it before it’s consumed.

UK food safety legislation places requirements on food manufacturers to ensure that any food they place on the market is safe for us to eat. Strict food safety procedures must be in place to ensure that any foods that are manufactured don’t contain dangerous levels of microbes. Naturally, manufacturers ensure that there is the longest possible selling period for the food, so they do all that they can to ensure a low level before placing it for sale/consumption. But ultimately there comes a point where the microbial growth has reached such a level that to consume the food would be hazardous, or even prove fatal.

One such organism that can have fatal consequences when eaten is Clostridium botulinum. Clostridium botulinum is a bacterium that produces dangerous botulinum toxins under low-oxygen conditions. Botulinum toxins are typically found in canned, preserved or fermented foodstuffs, such as smoked or raw fish, cured pork and ham, honey, corn syrup, and vegetables. There have also been reported cases of botulism from people consuming baked potatoes and oil infused with garlic. Botulinum toxins are one of the most lethal substances known to man, as they block nerve functions and can lead to respiratory and muscular paralysis.

Foodborne botulism, caused by consumption of improperly processed food, is a rare but potentially fatal disease if not diagnosed rapidly and treated with antitoxin.

To ensure the safety of the contents, canned goods are subjected to a process known as a “Botulinum cook”. This process uses a pressure cooker to heat the freshly canned food to 121oC for three minutes which ensures destruction of virtually all the spores of Clostridium botulinum.

Naturally things do go wrong in food production plants, both unplanned and deliberate. Below you can see the result of a failed botulinum cook process that also allowed all manner of other microbes to grow in the low oxygen atmosphere of the can. These photos were taken by a friend of mine in February 2018. He’d bought two cans of tuna from the same batch & both cans looked very similar on the inside. A clear indication that there must have been something wrong in the production process.

This is what happens when a “Botulinum Cook” fails!


I hope that this brief look into the world of food borne illness and food poisoning has helped to illuminate the reasons why there are use by dates on all food products; even water!

So now that you know why they’re there, what is the oldest date you’ve found on a can/jar at the back your cupboard? Would you still eat it?

If you want to learn more about food safety, whether purely for home use or because you work in the food industry, or range of courses will cover exactly what you need to comply with the food safety legislation in the UK. We also run face to face courses, so to discuss your training, drop me an email today.

Chris Garland. Founder and lead instructor at Chris Garland Training.
Chris Garland. Founder and lead instructor at Chris Garland Training.

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Use by dates, Food poisoning & Foodborne diseases

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