Microbiome science

Sauerkraut

Also called: fermented cabbage, kraut

Sauerkraut is fermented cabbage, made by salting shredded cabbage and letting Lactobacillus species ferment it for 1 to 4 weeks. It is one of the simplest fermented foods, contains live lactic acid bacteria, and adds variety to gut diversity. Like kimchi, it is high in salt; 1 to 2 tablespoons a day is a sensible serving.

How it is made

Shredded cabbage is mixed with about 2 percent salt by weight, packed into a jar to keep the cabbage submerged in its own brine, and left at room temperature for 1 to 4 weeks. Salt selects for Lactobacillus and Leuconostoc species while suppressing pathogens. The end result is sour, slightly fizzy, and shelf-stable in the fridge for months.

What it offers

  • Live Lactobacillus species (mainly L. plantarum, L. brevis, L. mesenteroides).
  • Vitamin C (cabbage contributes; some preserved through fermentation).
  • Vitamin K1 and small amounts of K2.
  • Fibre from cabbage (preserved through fermentation).
  • Bioactive compounds from cabbage (sulforaphane, isothiocyanates).
  • Low calorie (15 kcal per 100 g).

Sauerkraut vs kimchi

  • Strain diversity: kimchi 10 to 30+ species, sauerkraut 5 to 15.
  • Heat: kimchi has chilli, sauerkraut does not.
  • Salt: similar (1 to 2 g per 100 g serving).
  • Vegan-friendly: sauerkraut almost always; kimchi often contains fish sauce.
  • Use: sauerkraut on sausages, salads, sandwiches; kimchi in fried rice, eggs, stews.
  • Both contribute to gut diversity in 4 to 12 week trials.

How to choose

  1. Refrigerated section, not pantry shelf. Shelf-stable sauerkraut is pasteurised; bacteria are dead.
  2. Look for 'unpasteurised' or 'live' on the label.
  3. Just cabbage, salt and (optionally) caraway seeds. Avoid added vinegar, which usually means it was fermented less and acidified to taste sour.
  4. Cloudy brine and slight effervescence are good signs of active live cultures.
  5. Or make your own: 5 minutes prep, 1 jar, 1 to 2 weeks at room temperature.

Common questions

Does cooking kill the probiotics?
Yes, above 46 C the bacteria die. Cooked sauerkraut still has fibre and flavour but no probiotic effect. Add to dishes after cooking, off the heat, to keep bacteria alive.
How much should I eat?
1 to 2 tablespoons a day is plenty. Start with 1 teaspoon if you are new to fermented foods to avoid gas. Build up over a week.
Is sauerkraut safe in pregnancy?
Yes from a reputable refrigerated source. Avoid homemade sauerkraut in pregnancy unless you are very confident in your hygiene, because rare contamination risks (Listeria) matter more then.
Why does my homemade sauerkraut smell bad?
Healthy fermentation smells sharp and lactic, not foul. Foul smells (sulphurous, putrid) usually mean the cabbage was not submerged and grew mould. Discard and start again. Brine should always cover the cabbage.

Sources