How to Store Opened Cans and Jars So They Last Longer

You open a can of chickpeas for a quick lunch, use half, and the rest sits in the fridge — still in the can, slowly picking up a metallic tang. Or a jar of pasta sauce lingers in the door for weeks until you’re no longer sure it’s safe. Opened cans and jars are one of the quietest sources of food waste in most kitchens, simply because we’re not quite sure how to handle them.

The good news is that keeping these leftovers fresh is easy once you know a few simple rules. Here’s how to store opened cans, jars, and their contents so they last as long as possible — and nothing ends up in the bin.

Never store food in an opened can

This is the single most important habit to build. Once a can is opened and exposed to air, the metal can start to react with the food, especially with acidic contents like tomatoes, pineapple, or anything in a vinegar-based sauce. That reaction can give food a metallic taste and, over time, affect its quality.

Instead, transfer any unused contents into an airtight container — glass or food-safe plastic — as soon as you’ve taken what you need. Label it with the date so you always know how long it’s been open. A simple strip of masking tape and a marker is all it takes.

Know how long opened cans last

Once transferred to a sealed container and refrigerated, most canned foods keep well for a few days. As a general guide:

• Beans, vegetables, and fruit: 3–4 days in the fridge.
• Tomatoes and tomato products: 5–7 days, thanks to their acidity.
• Coconut milk: 4–6 days; give it a stir before using as it may separate.
• Canned fish like tuna or salmon: 2 days, and keep it tightly sealed so it doesn’t flavour everything around it.

If you won’t use the leftovers in time, freeze them. Beans, tomatoes, and coconut milk all freeze beautifully — portion them into small containers or ice-cube trays so you can grab exactly what you need later.

Treat jars with the same care

Jars have one advantage over cans: they usually reseal. But that doesn’t mean they last forever. Once opened, the clock starts ticking even in the fridge.

• Pasta sauce: about 5–7 days refrigerated. Freeze the rest if you’re not using it soon.
• Pickles and olives: several weeks, as long as they stay submerged in their brine.
• Jam and preserves: up to a month or more; always use a clean spoon to avoid introducing mould.
• Pesto: around a week — smooth the surface and add a thin layer of oil on top to slow browning.

Wipe the rim before resealing so the lid closes cleanly, and always store jars upright to keep the seal intact.

Use clean utensils every time

Many jars go off early not because of time, but because of contamination. Dipping a used spoon — or worse, a knife that’s touched toast — into a jar introduces crumbs, bacteria, and moisture that speed up spoilage. For anything you expect to keep a while, like jam, mustard, or mayonnaise, always use a clean utensil. It’s a tiny habit that dramatically extends shelf life.

Keep an eye on the signs of spoilage

Trust your senses. Discard anything that smells sour or “off,” shows mould, has an unusual colour, or fizzes and bubbles when you open it — those are signs of fermentation you don’t want. With canned goods, never use anything from a can that was bulging, leaking, or badly dented before opening. If you’re ever in doubt, it’s not worth the risk. For a deeper guide, see our post on how to tell if food has gone bad.

Plan so you actually use them

The best way to avoid wasting opened cans and jars is to have a plan for the leftovers before you even open them. Half a can of tomatoes becomes tomorrow’s soup base; leftover coconut milk slips into a curry or smoothie; that last of the pesto tosses through pasta or spreads onto a sandwich. A little forethought turns “what do I do with this?” into “dinner’s half done.”

Tracking what’s open in your fridge makes this effortless. With Food Waste Manager, you can log opened items and get reminders before they expire, so nothing gets forgotten at the back of a shelf. Pair it with a few leftover transformation ideas and you’ll find those half-used cans and jars become some of the most useful things in your kitchen — not the most wasted.