Science Articles

Food Date Coding Decoded

Mon, 7th Nov 2011

What are best before dates, and do we really need to depend upon them...?

Emma Easton

Date codes on food products indicate the quality and safety of the food. It seems simple enough... but not always! The most common date codes on food are “best before” and “use by” but there are also “sell by” or “display until” dates, and to complicate matters further some products don’t seem to require date codes at all. So what do all these dates actually mean?

The short answer is that, before these dates, the quality and safety of the food is guaranteed, but eat them after that and it’s up to you to stomach the consequences. But don’t start tearing your hair out yet, because there are some simple tips and tricks to follow to help you decide what you should - or probably shouldn't - consume.

Let’s start with the easy ones, the ones that are there for the sellers rather than the customer. The “sell by” and “display until” dates are optional and are placed on packed products to indicate to sales staff when food needs to be marked down or taken off the shelf (this is generally a few days before the “use by” date). So, as long as you take note of the other date coding on the packaging, these foods are usually fine to consume after their “sell by” or “display until” date.

Here is where things get a little more complicated. The “best before” and “use by” dates provide a lot more information about the potential quality and safety of the food, and so these are the date codes to pay the most attention to. First, “best before” dates are put on food products that have a long shelf life - things like dehydrated foods, canned foods; in essence, non-perishable foods.

best before dates“Best before” indicates that, after this date has passed, the manufacturer says that you are no longer eating a quality product, or that the food may be “nutritionally unstable” and the texture, taste, colour and flavour are not what the manufacturer intended. Legally it can still be sold after this date and it is still safe to eat, provided it has been stored correctly and is not damaged – but it may not taste great though! The food is safe to eat because it has been preserved or made sterile during manufacturing. For instance, canned foods are “retorted” (sealed so air can’t get in and out), and pressure cooked, to prevent microbiological spoilage.

Microbiological spoilage is a fancy way of saying that microbes (bacteria, viruses and fungi) get in and ruin the food. Microbes are everywhere, including inside your body, and some are very beneficial: without yeasts and bacteria, we couldn't serve up culinary delights like bread, beer and cheese. But not all microbes are good.

Things like moulds (forms of fungi) growing on food probably won’t harm you if you eat them, but they can taste vile. But you can spot relatively easily the kinds of changes that these organisms unleash on the food, so it's easy to avoid them.

But more worringly, other microorganisms are much more malignant and can make you ill, sometimes fatally so. For example, the bacterial pathogen Salmonella is a common cause of serious food poisoning. Although this bug is carried harmlessly by chickens and other forms of poultry, if it gets into a human in a poorly cooked egg or piece of meat, it can make you seriously sick. Food poisoning is never nice and the signs are very hard to miss. Unfortunately, pathogenic microorganisms may not make their presence known in an item of food until they are present in very high numbers - tens of millions of microbes - and even then the effect on the food can be very subtle, so you may not realise you've even eaten something you shouldn't - at least until the bugs make their presence felt a few days later...

But back to date coding - while “best before” indicates quality changes for long-life foods, “use by” is the date to pay attention to, as it is put on food that will readily spoil at the hands - or should that be flagellae - of contaminating microorganisms. "Use by" dates are employed on products that have a short shelf life and particularly those that need refrigerating. They indicate that food is unsafe to eat after this date and cannot legally be sold. For reasons of safety, manufacturers usually apply a date that's a day or two before the real “use by” date to protect those people not paying attention or who insist on eating the food anyway. So the general rule is that something that's a day ot two past its “use by” date is probably not harmful, but more than a week over and you’re risking infection by pathogens.

So now you understand a little more about date coding, but who decides the date code and how it is determined? Food manuyfacturers set the date code through a combination of experience, legislation (dependent on the country or region) and shelf-life testing. During shelf life testing, the manufacturer takes a sample of the food (such as a crate of cans or a crate of milk) kept under different conditions and simply watches to see what happens over time. For long life foods, like cans, the room usually has an elevated temperature to speed up the process. Short life foods, like dairy products, are usually kept in a laboratory fridge. At specific time points (daily for short life, weekly or monthly for long life) a portion of the food is taken and tested for quality (taste, texture, flavour, colour) and microbe numbers and types. After a certain point, the food will lose quality or contain unsafe numbers of microbes. The date is set at a little bit before this time, to ensure that the food is eaten at a point where it is both safe and still of a high quality.

What about food that doesn’t have a date code? Legally, fruit and vegetables and some deli products don’t need to have a date code. Leftover and takeaway food also doesn’t have a date code. So how long is it safe to store them before tucking in? This comes down to common sense and a little bit of know how. Take-away food is meant to be eaten straight away, but as it’s cooked it will last for a short length of time. If you have any left, put it in the fridge and eat it hot the next day, but don’t leave it any longer. Deli food and leftover food, provided it is refrigerated, will usually last between 4 and 5 days. This is where common sense kicks in - if it looks or smells funny throw it away! Fruit and vegetables also come under the common sense rule - if it looks or smells funny, or is growing extra bits (unless it is a shoot!) then throw it out. If it’s a bit squishy but other than that looks and smells fine, just cut the squishy bit off! As an aside, squishy fruit usually makes the best cakes and desserts...

mouldy bread use by dateAs a rule, date codes are just a guide and to be meaningful depend on proper storage and food handling. A can with a “best before” date that has been dented or is bulging is NOT safe. Bulging cans mean that pathogens are in there and multiplying. Throw it away immediately - don’t even open it to try it. If you dented the can yourself then you don’t need to throw it away immediately, but you don’t want it in the cupboard for months on end. Try to use it up within the month you dented it. Always follow food storage instructions on the packaging, especially the “refrigerate after opening” instructions. The general rules for unopened, undamaged foods are: if it is on the supermarket shelf it can be stored in the cupboard; if it was in the refrigerator section then it belongs in the fridge and if it’s sold frozen keep it frozen. The mode of storage is determined by the potential of the food to harbour microbes; refrigeration and freezing slow down microbial growth.

So, with a little knowledge, date coding is quite simple. Pay attention to “use by” dates and keep “best before” in mind. Most importantly, store the food correctly, cook it well, and if it looks or smells bad, avoid eating it.

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