Tier 6 · Preserve

TO FERMENT

Letting selected microbes transform food deliberately, producing acid or alcohol that both flavours it and keeps rivals out.

Why it works

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.

How to tell

• 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.

When it goes wrong

White film on the surface.

Kahm yeast — harmless, caused by oxygen contact, and skimmed off. Fuzzy or coloured growth is mould and is different.

Soft, mushy vegetables.

Too little salt, too warm, or the vegetable was not fresh. Pectin-degrading enzymes have run ahead of the acidification.

Nothing happened at all.

Too cold, too much salt, or chlorinated water. Chlorine kills the bacteria you are relying on; let tap water stand or use filtered.

Mould on the surface.

Food above the brine line. Everything must stay submerged, which is what a weight is for.

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.

Where to practise it

It carries to

Recipes using it

Generated from recipe step verbs and ingredient preparation forms. It is never authored, and it cannot drift from the recipes.