Rescues · TO FERMENT
Soft, mushy vegetables.
Why it happens
Too little salt, too warm, or the vegetable was not fresh. Pectin-degrading enzymes have run ahead of the acidification.
Recovering it
Kahm yeast is skimmed and the ferment continues. Actual mould on a brined vegetable ferment means discarding the batch — the visible growth on a wet food is a fraction of what has spread through it, and this is not a place to take a chance. A ferment that has gone soft is safe if it smells right but the texture will not come back. One that is under-soured simply needs more time somewhere warmer.
The mechanism
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 TO FERMENT lesson — how to tell, where to practise it, what it carries to.