How do I store opened tins and jars?

The common advice not to store food in an opened tin is correct, and the reasons are practical rather than alarming.

Safety

Step by step

1. Decant everything out of the tin.Once opened, the lacquer lining is broken at the cut edge and metal can transfer into acidic contents. It also cannot be sealed properly and the cut edge is sharp.
2. Use glass or food-grade plastic.An airtight container. Glass is better for strongly coloured or oily foods, which stain and hold odours in plastic.
3. Refrigerate immediately.Everything, once opened, including things that sat in a cupboard for a year. The processing that made it shelf-stable ended when the seal broke.
4. Know the rough timings.Most opened tinned foods three to four days. Tomatoes and other high-acid contents two to three. Opened tinned fish, use within a day or two.
5. Read the jar label.Jars vary far more than tins. Some say use within three days, others within six weeks. Mayonnaise, pesto and cook-in sauces are shorter than most people assume.
6. Keep the contents submerged where relevant.Olives, capers, sun-dried tomatoes and preserved things keep far longer under their liquid or oil. Anything exposed above the surface spoils first.
7. Use a clean spoon, every time.The main cause of a jar spoiling early. A used knife or a finger introduces bacteria and moisture, and jam and nut butter both show it as surface mould.
8. Wipe the rim before closing.Residue on the thread stops the lid sealing and grows mould. Ten seconds and it noticeably extends the life of a jar.
9. Label with the date opened.Masking tape and a pen. A jar of anything in the fridge door is unidentifiable after a fortnight, and guessing tends towards optimism.
10. Freeze what freezes well.Tomato purée, coconut milk, stock and beans all freeze usefully. Ice cube trays for purée and small portions, then into a bag.
11. Know what does not freeze.Mayonnaise splits. Cream-based sauces separate. Whole soft fruit collapses. Freezing solves many storage problems but not these.
12. Throw out anything doubtful.Bulging lids, mould, fermenting smell, fizzing. None of these are worth investigating further, and none are fixed by removing the affected part.

Tips

• Decant out of the tin, always. It takes seconds and it removes both the metal and the sharp edge.
• Clean spoon every time. It is the difference between a jar of jam lasting weeks and growing mould in ten days.
• Date the lid with tape. Guessing how long something has been open is always optimistic.

Common mistakes

• Leaving food in the opened tin — The lining is cut at the rim so metal can transfer into acidic contents, it cannot be sealed, and the cut edge is a genuine hazard in a fridge.
• Using a knife that has touched something else — It introduces bacteria and moisture, which is what causes the surface mould that appears on jam and nut butters long before their date.

If it doesn't work