Is my ferment normal?

Signs that are normal

All of these are a ferment working. None is a reason to stop.

Cloudy brine

A population of lactic acid bacteria. This is what success looks like, and clear brine after several days is more concerning than cloudy.

Bubbles, fizzing, a hiss when opened

Carbon dioxide. Vigorous in the first days, then quieter.

A sour smell, getting stronger

Lactic acid accumulating. The single best indicator that things are going right.

White sediment at the bottom

Settled bacteria and vegetable matter.

Brine overflowing in the first days

Gas pushing liquid up. Stand the jar on a plate.

Colour changes

Bright green cucumbers turn olive; red cabbage bleeds; garlic occasionally turns blue or green, which is a harmless reaction between its sulphur compounds and trace metals.

Softening at the very top

Where brine contact is least. Push everything down.

Signs that mean act, but not panic

A flat, wrinkled white film on the surface

Kahm yeast. Harmless but it tastes unpleasant and it softens the ferment. Skim it, and fix whatever let air reach the surface.

No bubbles at all

Usually the room is cold, or the vigorous phase has passed. Judge by taste — see a ferment that is not bubbling.

Very slow progress

Cold, or heavily salted. Move it somewhere warmer.

It has gone very sour

It went further than you wanted. Refrigerate to stop it, and use it in cooked dishes where sourness is an asset.

Soft texture

A quality failure, not a safety one. See soft fermented vegetables.

Signs that mean throw it out

Do not reason your way past any of these.

Fuzzy, raised or coloured growth

Mould — blue, green, black, pink, grey or furry white. Discard the whole jar, not just the top.

A putrid, rotten or faecal smell

Not sourness. Sour is right; rotten is not, and the difference is unmistakable when you meet it.

Slimy, ropy, viscous brine that strings off a spoon

Discard. Note that this is different from the intended stickiness of natto, which is a deliberately cultured food.

A smell of solvent, nail varnish or strong alcohol

The wrong organisms have taken over.

Anything you are genuinely unsure about

Throw it out. A jar of vegetables is cheap and this is not a judgement worth gambling on.

The one thing worth being clear about

Spoilage is not the same as a hazard, and neither one is proved by how something looks or smells.

Those are two separate statements and both matter. A ferment that has gone soft, yeasty or unpleasantly sour is spoiled in the sense that it is no longer nice to eat, and that is usually not a safety question at all. Meanwhile a food that looks and smells completely normal is not thereby safe — appearance is not a test for the things that actually make people ill.

Which is why the guidance on this page is deliberately asymmetric. The normal signs are reassuring because they are the recognised signature of the process working. The bad signs mean stop. But "it looks fine" is never the whole argument for eating something, and following a method from a reliable source is what actually does the work. FoodHQ does not publish salt percentages, pH figures or keeping times for home preserving. Those are safety numbers, they are set by a food safety authority rather than by a cookery writer, and the right ones depend on what you are fermenting and where you are. In the UK the Food Standards Agency is the authority — use a recipe from them or from another body with the same standing, and treat this page as the explanation of why that recipe is shaped the way it is.

Common questions