2% salt by weight, cabbage fully submerged under a glass weight, 20C in a cupboard. Day five there's a thin white film across the whole surface, wrinkled like the skin on cooling custard, no fuzz and no colour. Smells sour and cabbagey rather than off. I've read fifteen conflicting things. What's the actual test?
Photograph it against a dark background with light coming across the surface if you're unsure. The fuzz on mould is obvious in a raking light and completely invisible in a phone photo taken from directly above in a bright kitchen.
The submerged rule is doing all the work here. Any shred that floats up and dries out becomes the launchpad for actual mould, and a glass weight always leaves a gap round the edge. A folded outer cabbage leaf under the weight fixes that for free.
There were a couple of shreds stuck to the glass above the brine line. Fixed.
Airlock or a loose lid? Not because an airlock prevents kahm, it doesn't reliably, but a jar you burp daily gets fresh air across the surface every time, and kahm loves that.
Also, 2% by weight of what? It should be the cabbage plus any added water, not the cabbage alone. Getting that wrong is how people end up at 1.4% wondering why things are lively.
@weatherfront_wu · 3mo ago · 3 replies
Flat, wrinkled, white, no fuzz, and it re-forms as a skin after you disturb it. That's kahm yeast and it's harmless. Mould is fuzzy and three-dimensional, grows in distinct circular colonies rather than an even film, and is usually blue-green, black or pinkish. The other tell is that kahm sits on the liquid surface while mould generally starts on something poking above it.
Skim what you can, make sure everything is back under the brine, carry on. It'll return if the ferment is warm and slow. 20C is a bit warm for kraut and low salt plus warmth is exactly the kahm-friendly combination, so next batch try 2.25-2.5% and somewhere nearer 18C.
Honest caveat: fuzz, any colour, or a genuinely foul rather than sour smell means throw it out. Not worth the argument.
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@mulch_marta · 3mo ago
Definitely flat and skin-like, no colour anywhere. Skimmed it and it came back in two days exactly as described.
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@keg_line_ken · 3mo ago
Kahm returning isn't a failure. Skim and keep going. The flavour impact at this stage is minimal, though weeks of it can add a yeasty note.
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