Troubleshooting a Fermentation Batch That Went Wrong

How do I work out what went wrong?

Ask the questions in the order that rules out the most. First: has it acidified? That one answer separates a batch with a flavour problem from a batch with a safety problem, and everything else is easier to interpret once you know it. Cheap pH strips are enough; a meter is better if you ferment often.

Second: what temperature has it actually been at? Not the thermostat — the shelf. A jar beside a radiator and a jar in an unheated pantry are running two different experiments, and most reports of nothing happening come from the second one.

Third: was everything under the brine, and what was the salt? Weigh it, do not estimate. A tablespoon of flaked salt weighs nearly half what a tablespoon of fine salt does, and that difference is the gap between 2% and 1.2%.

Only then look at the symptom itself. Diagnosing from the symptom first is how people end up adding salt to a batch that was simply cold.

Why is nothing bubbling?

Usually because it is cold. Below roughly 18 °C a vegetable ferment can take a day or two before anything is visible, and in a genuinely cool room it may never produce the vigorous fizzing you expected while still acidifying perfectly well. Move it somewhere warmer and give it another day before concluding anything.

The second common reason is that the vessel is not closed enough to show it. Carbon dioxide escaping freely past a loose lid never collects into visible bubbles. Absence of bubbles is not absence of activity — which is exactly why the pH reading matters more than the theatre.

The third is salt. Above about 5% fermentation slows dramatically; the product stays crunchy and sharply salty and does very little. That one is recoverable by diluting the brine, though the texture will not come back.

Why has it gone soft or slimy?

Soft means the pectin holding the vegetable's structure has been broken down, and there are three routine causes: too little salt, too much heat, or pectinase-producing organisms introduced with untrimmed cucumber blossom ends. The blossom end is worth singling out because it is invisible as a cause and trivial as a fix — cut a few millimetres off it.

Sliminess in the first days is often something else entirely, and often fine. Leuconostoc species produce dextran early in a ferment, which makes the brine ropy and alarming, and it usually resolves as the succession moves on and the pH falls. Slime that appears early and disappears is normal; slime still there in week two is not.

Temperature is the lever people forget. Above roughly 27 °C, softening organisms outpace the lactic acid bacteria, and the batch turns to mush before acidity can protect it.

Why does it smell wrong?

Sour is right. Yeasty, bready or faintly solvent-like is common early and usually passes. Sulphurous is normal for brassicas — cabbage, cauliflower and broccoli all smell unpleasant in the first week, and that is not a fault.

Putrid is the one that matters. A smell that reads as rotting or faecal rather than sharp is a different class of organism, and it does not resolve with time. The distinction people struggle with is that both can be strong; the question is not intensity but character. If you find yourself arguing with your own nose about whether it is sour-bad or rotten-bad, treat it as rotten.

Vinegary is fine on a kombucha or a long vegetable ferment, and simply means acetic acid bacteria have had oxygen and time.

When is a failed batch actually dangerous?

When it did not acidify. A vegetable ferment still above pH 4.6 after roughly seventy-two hours at room temperature has not established the condition that makes fermentation a preservation method, and it should be discarded or restarted rather than given more time. That is the case worth being strict about, and the only one where the answer is unambiguous.

Fuzzy coloured surface growth on a liquid ferment is the other clear discard. So is a pink-orange slimy brine, and so is persistent sliminess past the first week combined with an off smell.

Everything else here — no bubbles, soft texture, a white film, an aggressive brassica smell — is a quality problem. Those are worth fixing, but they are a different question, and conflating the two is how people either throw away good food or eat something they should not have.