Every other page in this domain is about doing the process correctly. This one is about the jar in your hand that you are not sure about, at the point where the process is already behind you.
It is the shortest decision in the domain and the one most likely to be got wrong, because the instinct everyone has is exactly the wrong one.
The rule that governs this page
Signs a jar has failed
Any one of these means discard. Not investigate, not smell, not open carefully. Discard.
Before opening:
- The lid is bulging, domed upward, or has popped. Gas production inside is the clearest single sign of microbial growth.
- The lid flexes when pressed, or the seal has gone.
- Liquid has seeped or dried around the rim or down the side. Something forced its way out.
- The contents are unusually cloudy, where they were clear.
- Bubbles rising in the jar when it has been standing still.
- Mould, of any colour, anywhere, including on the underside of the lid.
- The food has changed colour noticeably, darkened unevenly, or separated in a way it did not before.
- The jar is leaking, however slightly.
- Rust or corrosion on the underside of the lid.
On opening:
- A spurt, a hiss beyond the normal gentle release, or liquid spraying out. Pressure inside means gas, means growth.
- A smell that is off, yeasty, fermented, cheesy or fizzy. A smell is proof of a problem, though the absence of one proves nothing.
- Bubbling or fizzing as it opens.
- Slimy, ropy or stringy texture.
Contextual failures, regardless of appearance:
- The jar was processed by the wrong method. Any low-acid food that was water-bathed rather than pressure canned. Discard the whole batch, however good it looks. This is the most important line on the page.
- A jar that never sealed properly and was left in the cupboard anyway.
- A jar whose process time or recipe you are not sure about.
- A jar from a batch where another jar has failed. They were processed together in the same conditions.
- Anything stored somewhere warm for an extended period.
- Anything unlabelled and of unknown age.
Things that look wrong and are not
Balance matters, because throwing away good food in a shortage is its own harm.
| What you see | Verdict |
|---|---|
| Fruit floating above the syrup | Fine. Density and pack method, purely cosmetic |
| Liquid level dropped, food still covered | Fine. Siphoning during cooling |
| Liquid level dropped, food now exposed above it | Quality loss and discolouration. Safe if sealed, but eat it sooner |
| Cloudy brine in pickles | Usually table salt with anti-caking agent, or hard water. Fine |
| White crystals in jam or fruit | Usually sugar crystallisation or harmless tartrate. Fine |
| Jam darker at the top | Oxygen in the headspace. Cosmetic |
| A layer of separated liquid in tomato products | Normal separation. Fine |
| Slight metallic taste after long storage | Lid contact. Not dangerous, quality declining |
| Sediment at the bottom of fruit juice | Normal |
Any doubt at all, and the earlier rule wins. These exceptions exist so you do not throw away a good year's work; they do not soften the discard list above.
The decision
Work through it in this order and stop at the first answer.
- Was it the right method for the food? Low-acid food water-bathed is a discard, immediately, whatever it looks like.
- Is the seal intact and the lid concave? If not, discard.
- Any sign from the failure list? If yes, discard.
- Do you know the recipe, the process time and the date? If not, discard.
- If all four are clear: the jar is as safe as the process that made it, which is the only assurance available.
The 10-minute boil. For home-canned low-acid food that has passed every check, the standard extra precaution is to boil the contents hard for 10 minutes before eating, plus one minute per 1,000 feet of altitude. Botulinum toxin, unlike the spores that produce it, is destroyed by that.
Disposing of a suspect jar
This matters more than people expect, because the toxin is dangerous outside the jar too.
If the jar is still sealed and you are discarding it unopened: put it, intact, in a sealed heavy-duty bag, then into a second bag, and into the bin. Do not open it.
If the jar is already open:
- Do not pour it down the sink or onto the compost, and do not feed it to animals. Chickens, pigs and dogs are all susceptible.
- Wear gloves if you have them. The toxin can be absorbed through broken skin and through the eyes.
- Detoxify it if you can do so safely: boil the food and the jar, submerged, for 30 minutes. Then it can be disposed of normally.
- If you cannot boil it, double-bag the jar and contents and bin it.
- Decontaminate every surface the contents touched with a bleach solution, roughly one part household bleach to five parts water, left in contact for at least 15 minutes. Worktops, the sink, the opener, the spoon, your hands.
- Wash your hands thoroughly afterwards regardless.
Symptoms, and what to do
Botulism symptoms typically appear 12 to 36 hours after eating, though the range runs from a few hours to several days.
It is a paralysis that starts at the head and works down, which is what distinguishes it from ordinary food poisoning:
- Double or blurred vision, drooping eyelids
- Slurred speech
- Difficulty swallowing
- Dry mouth
- Facial weakness
- Then descending weakness in the arms, the trunk, the legs
- Then difficulty breathing
Nausea and vomiting may occur but often do not, and their absence is not reassurance.
In an emergency with no medical services reachable, there is no home treatment for botulism. That is a hard thing to write and it is the truth, and it is the strongest argument in this entire domain for getting the process right the first time rather than relying on judgement afterwards. If you have no pressure canner, do not can low-acid food. Dry it, ferment it, salt it or pickle it instead.