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Vegetables ferment

Sauerkraut

Beginner

Shredded cabbage and salt, fermented under its own brine — the classic tested vegetable ferment.

Temperature
15.5–24 °C
NCHFP: 70–75 °F (21–24 °C) is best; 60–65 °F (15.5–18 °C) takes 5–6 weeks; below 60 °F it may not ferment; above 75 °F it may soften.
Time
3–4 weeks at 21–24 °C; 5–6 weeks at 15.5–18 °C
Done when bubbling stops and the kraut is evenly sour.
Salt
About 2–2.5% of cabbage weight (NCHFP: 3 tbsp canning salt per 5 lb)
Don't reduce salt: NCHFP warns against making sauerkraut with less salt than the recipe requires.
Acidity (safety control)
pH 4.6 or below — ideally under 4.0 before cold storage
Acid made by lactic bacteria is what keeps vegetable ferments safe; 4.6 is the regulatory boundary for acid foods. Check with pH strips (narrow range) or a calibrated meter. Smell and taste are not a safety test.

Timeline

Sauerkraut timeline

  1. Stage 1: Shred, salt, packstart · about 1 h

    Hands-on — Weigh the salt

  2. Stage 2: Active ferment (bubbly)from 1 h · about 10 days

    Fermenting / waiting — 21–24 °C, keep submerged, skim scum

  3. Stage 3: Souring completesfrom 10 days · about 18 days

    Fermenting / waiting — Bubbling slows, then stops

  4. Stage 4: Refrigeratefrom 4 weeks · keeps about 12 weeks

    Cold storage — Fridge: several months

Ingredients

  • Firm white cabbage
  • Canning or pickling salt (no iodine or anti-caking agents) — NCHFP: 3 tbsp per 5 lb (2.3 kg) of shredded cabbage

Equipment

  • Kitchen scale
  • Food-grade crock, glass jar or food-grade plastic container
  • Weight (water-filled bag, plate, fermentation weights)
  • Cover

Steps

  1. Remove outer leaves; quarter, core and shred the cabbage finely.
  2. Weigh it and mix in salt at the tested rate (NCHFP: 3 tbsp canning salt per 5 lb).
  3. Pack firmly into the container, pressing until juice rises over the cabbage.
  4. Weigh it down so the cabbage stays under the brine; if there isn't enough juice after 24 hours, top up with brine of 1½ tbsp salt per quart (about 1 litre) of water.
  5. Ferment at 21–24 °C. Check 2–3 times a week and skim any scum.
  6. When bubbling stops and it's evenly sour (about 3–4 weeks at 21–24 °C), refrigerate or can by a tested method.

Is it working?

  • Pale yellow-translucent cabbage, crisp-tender
  • Clean, sour, pickle-like smell
  • Bubbling during the first weeks, then settling

Smell & texture: Sour and cabbagey (it can be sulphurous early on — that fades). Crisp, not mushy.

Signs tell you it's fermenting, not that it's safe: never rely on smell or appearance alone.

Safety, mould and discard rules

Mould or yeast?

A thin, flat, white or cream film on the brine surface is usually kahm yeast: skim it off promptly, because it feeds on the acid and can raise the pH. Anything fuzzy, raised, or coloured (blue, green, black, pink, orange) is mould: discard the whole batch, including the brine. If you can't tell which it is, discard.

Storage

Refrigerate tightly covered when fully fermented, or can it by the NCHFP tested process. It is not shelf-stable otherwise.

Shelf life: NCHFP: fully fermented kraut may be kept tightly covered in the refrigerator for several months.

The science: what's happening

Salt pulls water from the cabbage to make a brine and holds back spoilage microbes. Salt-tolerant lactic acid bacteria naturally on the cabbage take over in a strict sequence (Leuconostoc first, then Lactobacillus/Lactiplantibacillus species), turning sugars into lactic acid until the kraut is sour and the pH is low.

Organisms

  • Leuconostoc mesenteroides (early)
  • Lactiplantibacillus plantarum, Levilactobacillus brevis and others (later)

Troubleshooting

Soft kraut
Too little salt, too warm (>24 °C), or cabbage not kept under the brine. If it's slimy too, discard.
Not enough brine
After 24 hours, top up with 1½ tbsp salt per quart of water.
White film on top
Likely kahm yeast — skim it off. If fuzzy or coloured, it's mould: discard.
Dark or brown on top
Exposed to air — the layer above the brine has oxidised. Remove the top; if there's mould, discard.

A dish (not a ferment) gone wrong? Try Recipe Rescue.

Cook with it

Learn more

Sources

Guidance changes: check the source for current wording. Original text; figures quoted from the sources where stated.