Before opening: look at the lid
- The lid is bulging or domed instead of slightly hollow.
- On a twist-off jar, the centre of the lid moves up and down and clicks when you press it.
- On a rubber-seal jar, the lid comes off without resistance when you pull the tab of the seal.
- There are traces of leakage, sticky marks or rust around the lid.
Any one of these signs means the vacuum is gone: the jar is no longer protected and must be discarded.
When opening: what should worry you
- Liquid spurts out or foams as soon as the jar is opened.
- An unusual smell: sour, rancid, fermented or rotten (except, of course, for lacto-fermented vegetables, whose sour smell is normal).
- Mould on the surface or under the lid, whatever its colour.
- A brine that should be clear has turned cloudy, or bubbles rise in a jar that has not been moved.
- Food that has become soft, slimy or discoloured.
Botulism: why you never taste a doubtful jar
Clostridium botulinum develops in low-acid foods — vegetables, meat, fish, mushrooms — that were not processed long or hot enough. Its toxin can be present without any visible sign, smell or change of taste, and a tiny amount is enough to cause a serious illness.
So never taste a jar to check it. If a low-acid jar shows the slightest warning sign, or if you are not sure how it was processed, throw it away without tasting it.
Blurred or double vision, drooping eyelids, difficulty swallowing or speaking, muscle weakness in the hours or days after a meal: call the emergency services immediately and mention the preserve you ate.
How to throw away a suspicious jar
- If the jar is still closed, do not open it: put it whole in a closed bag, in the household waste, out of reach of children and animals.
- If it has leaked or been opened, wear gloves, avoid splashes and clean every surface that touched the contents with diluted bleach, then wash your hands thoroughly.
- Never give the contents to animals and do not put them in the compost.
The jar did not seal: what to do
Check every jar 24 hours after processing. A jar that did not seal is not lost if you act quickly:
- either put it in the fridge and eat it within a few days, like a fresh dish;
- or process it again within 24 hours, with a new seal or lid and the full processing time.
Past 24 hours at room temperature, do not process it again: throw it away.
Why a jar fails to seal
- A chipped or cracked rim — run your finger around it before filling.
- Food or juice left on the rim when closing.
- A reused seal or twist-off lid that has lost its elasticity.
- A wrong headspace: too full, the contents overflow; too empty, the air left in the jar prevents the vacuum.
- A processing time that was too short, or a thermal shock when taking the jars out.
Good habits that avoid most losses
Follow tested recipes, write the content and the date on every jar, check the seals after 24 hours and eat the oldest jars first. An up-to-date inventory tells you which jars have been waiting too long — Jarrito keeps it for you, batch by batch.
