How long does tinned food really last?

Tins are the backbone of most emergency food stores, and for good reason: they're sturdy, they don't need a fridge, and they keep for a long time. But "a long time" isn't forever, and the date on the label doesn't always mean what people think. Here's how to judge a tin safely.

What the date on a tin means

There are two kinds of date on food, and they mean different things:

• Best before is about quality. After it, food may not be at its best, but it isn't necessarily unsafe if it has been stored properly and the packaging is undamaged.
• Use by is about safety. Food shouldn't be eaten after its use-by date, even if it looks and smells fine.

Most tins carry a best-before date. Here's what official guidance in New Zealand says:

What affects how long a tin keeps

• Temperature. Heat speeds up changes in flavour, texture and colour. A cool, steady spot is best.
• Moisture. Damp causes rust, and rust can damage the seal.
• The food inside. Different foods change at different rates, which is why dates vary between tins.
• Handling. Dropped or crushed tins can be damaged in ways that let bacteria in.

Storage conditions

Keep tins somewhere cool, dry and dark, off the floor, and away from ovens, boilers, radiators and direct sun. Avoid places that freeze or get very hot, such as some garages and lofts.

Warning signs: when to throw a tin away

Don't eat food from a tin that is:

• Bulging or swollen, or with a lid that bounces back when pressed.
• Leaking, or with stains or residue on the outside.
• Badly dented, especially along the seams or rim.
• Deeply rusted, rather than just marked on the surface.
• Spurting liquid or giving off a bad smell when opened.

If in doubt, throw it out. It isn't worth the risk, especially for children, older people, pregnant women or anyone who is unwell.

Once a tin is opened

An opened tin is no longer long-life food. Transfer any leftovers into a clean, covered container, put them in the fridge, and use them within the time the label gives. In a power cut, that's a reason to stock smaller tins you can finish in one go.

A five-minute tin check

Every month or two, take a quick look along your tins:

1. Check each date and bring anything due soon to the front.
2. Run your eye along the seams and rims for dents, rust or stickiness.
3. Press the lids: they shouldn't move or bulge.
4. Move any damaged tins out and throw them away safely.
5. Make a note of what you need to replace.

Choosing tins to stock

Pick tins your household already eats, in sizes you can finish in one go. Ring-pull tins are handy in an emergency, but keep a manual tin opener anyway. Check allergens on every label, and look for options that suit special diets, such as lower-salt or no-added-sugar versions where that matters to someone at home.

A simple rotation guide

1. Put new tins at the back and move older ones forward.
2. Check dates every month or two.
3. Use anything nearing its date in normal meals.
4. Replace what you use on your next shop.

SupKit does this for you: it reads the date when you add a tin, tells you what to use first, and reminds you before anything is due. See how to rotate emergency food for the full routine.