When it goes wrong · Ferment
Mould on the surface.
Can you save it?
Reviewed for this symptom
Discard the batch. On a wet vegetable ferment the visible growth is a fraction of what has spread, and it is not worth the chance. Clean the crock, and weight everything under the brine next time.
Safety boundary: Mould on a brined ferment means the whole batch is discarded; never skim mould and continue.
How to confirm the diagnosis
Observable cues, not inferred user state
- Fuzzy, raised or coloured growth
- Vegetables were above the brine line
- No weight was used
Not this?
What actually happened
Only this symptom
Food above the brine line. Everything must stay submerged, which is what a weight is for.
The full mechanism
Shared by every ferment failure
Fermentation is controlled spoilage, and the control comes from making conditions that one organism tolerates and others do not. In vegetables, salt at roughly 2% by weight is enough to inhibit most spoilage bacteria while lactic acid bacteria — already present on the vegetable — carry on. They convert sugars to lactic acid, the pH falls, and below about 4.6 almost nothing dangerous can grow, so the ferment protects itself as it proceeds. Submersion matters for the same reason: the useful bacteria work without oxygen, and the moulds and yeasts that spoil a crock work only with it, so anything above the brine line is at risk while everything below is safe. In dairy, the same acidification makes casein clump, which is the thickening in yogurt and crema. In bread, wild yeast and lactobacilli produce gas and acid together.
The full Ferment lesson — how to tell, where to practise it, what it carries to.
Next time
Prevent this specific failure
Everything submerged under a weight, a full jar, and a cool spot.
What right looks like
Shared by every ferment failure
- Bubbles appear within a day or two and the brine turns cloudy — both are signs it is working, not spoiling.
- The smell is sharply sour and clean. Anything yeasty, cheesy or putrid is a different organism.
- Vegetables lose their bright colour and go translucent as the acid works into them.
- Taste is the real gauge, and it should be sour enough to make you flinch slightly before it is done.