Interactive lesson

Fermentation problems, step by step

Interactive lesson: eyes, nose and a pH strip before the spoon — kahm yeast or mould, soft and pink kraut, fermentation that won't start, health and when to throw it out.

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The whole lesson as text

1. How to read a ferment

Every check goes in the same order: eyes, nose, fingers, pH strip, and the mouth only at the end.

Eyes first — Look at the surface, the colour and whether everything is submerged. Pink, brown or black colour in the cabbage is not normal.
Then the nose — The smell should be cleanly sour and cabbagey. In the first 7–10 days it may also be "sulphurous".
Fingers and fork — Feel with a clean fork: the vegetables should be firm, not soft and mushy.
pH strip, then the spoon — A finished ferment has a pH of 4.0 or lower. Taste only when everything else is fine; anything suspect isn't tasted, not even from the tip of a spoon.

Why: When the kraut goes soft or a film appears on the brine, you have to decide: normal, fixable or thrown out. That decision isn't made "by taste", but by signs that can be learned.

Check every vessel every week, and write every problem in the log.
Cloudy brine, white sediment at the bottom and bubbles during fermentation are normal.

2. Kahm yeast or mould

This question decides whether the whole crock goes.

Flat white film — A thin, flat, white to cream film lying as a layer on the brine, sometimes wrinkled: this is usually kahm yeast.
Furry mould — Fluffy, round colonies, green, blue, black, grey or pink, on vegetables sticking out or on the rim of the vessel: this is mould.
Skim off the kahm — Skim off the film as soon as it appears, then wash the board and weight.
Find the cause — Kahm comes when the brine is in contact with air: too little brine above the board, too much air under the cover, too warm.

Why: Kahm yeast isn't dangerous in itself, but it uses up the acid at the surface and opens the way to bacteria that soften the cabbage. Some moulds produce toxins (mycotoxins) that cooking doesn't destroy.

Kahm smells mildly yeasty, sometimes "cheesy". Mould smells musty, cellar-like, earthy.
A common mistake: a white kahm film taken for mould and a whole crock of good kraut thrown out.