Knowledge Base

Sauerkraut

Vegetable ferment · Traditional · peer-reviewed

Cabbage and salt, nothing else — a self-selecting lactic ferment where the vegetable's own bacteria acidify the brine and preserve it for months.

Easy to make
14–28 days ferment
live-cultures, lactic-acid, vitamin-c supplied

Ingredients

  • Green or white cabbage, shredded1 kg
  • Non-iodised salt (2% of cabbage weight)20 g

How to make it

  1. Step 1

    Shred cabbage finely, discarding the tough outer leaves (keep one whole leaf aside).

  2. Step 2

    Weigh the shredded cabbage and add 2% of that weight in salt.

  3. Step 3

    Massage 5–10 minutes until the cabbage weeps enough brine to cover itself.

  4. Step 4

    Pack tightly into a jar so the brine rises above the cabbage. No dry cabbage should touch air.

  5. Step 5

    Lay the reserved leaf on top and weigh it down. Cover loosely so CO₂ can escape.

  6. Step 6

    Ferment 2–4 weeks at 18–22 °C, out of direct sun. Taste weekly.

  7. Step 7

    When pleasantly sour, seal and refrigerate. Keeps several months cold.

What it is

Sauerkraut is cabbage preserved by lactic-acid fermentation. Salt draws water out of the shredded leaves to form a brine, and the lactic-acid bacteria (LAB) that already live on the cabbage do the rest — converting sugars into lactic acid until the environment is too acidic for spoilage and pathogenic microbes to survive. No starter culture is needed; the process self-selects for the right microbes.

The science

Fermentation follows a well-documented microbial succession. Early on, the heterofermentative species Leuconostoc mesenteroides dominates, producing lactic acid, acetic acid and CO₂ and dropping the pH. As acidity rises it gives way to more acid-tolerant homofermentative species, chiefly Lactiplantibacillus plantarum (formerly Lactobacillus plantarum), which drive the pH down to roughly 3.4–3.6 and set the finished flavour (Plengvidhya et al., 2007).

Two conditions make this safe and reliable: an anaerobic environment (vegetables submerged under brine) and a salt concentration around 2% by weight, which favours LAB while suppressing competitors (Breidt et al., 2013).

Safety

The safety of fermented vegetables comes from rapid acidification, not heat. Keep everything submerged, hold near 18–22 °C, and the pH should fall below 4.6 within days. Discard a batch that smells putrid, turns slimy, or grows fuzzy coloured mould (a flat white film of kahm yeast is harmless and can be skimmed). Use non-iodised salt — iodine and anti-caking agents can inhibit the culture.

Signs it worked / troubleshooting

  • ✅ Good: cloudy brine, steady tang, clean sour-cabbage smell.
  • ⚠️ White film on the surface = kahm yeast → skim it, keep cabbage submerged.
  • 🚫 Fuzzy blue/green/black mould or rotten smell = contamination → discard.

How to store

Once it reaches a sourness you like, refrigerate. Cold storage nearly stops the ferment; sealed and submerged, sauerkraut keeps for several months.

References

  • Plengvidhya V, Breidt F, Lu Z, Fleming HP (2007). DNA fingerprinting of lactic acid bacteria in sauerkraut fermentations. Applied and Environmental Microbiology 73(23):7697–7702. doi:10.1128/AEM.01342-07
  • Breidt F, McFeeters RF, Pérez-Díaz I, Lee CH (2013). Fermented Vegetables. In: Food Microbiology: Fundamentals and Frontiers, 4th ed. ASM Press, 841–855. doi:10.1128/9781555818463.ch33
  • Touret T, Oliveira M, Semedo-Lemsaddek T (2018). Putative probiotic lactic acid bacteria isolated from sauerkraut fermentations. PLoS ONE 13(9):e0203501. doi:10.1371/journal.pone.0203501

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