Does cooking kill the probiotics?

Yes, sustained heat kills the bacteria; lactic acid bacteria stop growing above about 45 C and are progressively killed at cooking and pasteurisation temperatures. 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?

Pasteurised (shelf-stable) sauerkraut is the safer choice in pregnancy. Unpasteurised live sauerkraut, including refrigerated and homemade jars, is best avoided, because Listeria can grow even at fridge temperatures and pregnancy raises the risk of serious infection. If in doubt, cook it until steaming hot or check with your midwife.

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.

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 (isothiocyanates and other glucosinolate breakdown products).
Low calorie (about 19 kcal per 100 g).

Sauerkraut vs kimchi

Strain diversity: kimchi is generally more diverse than sauerkraut, with its garlic, ginger and fish sauce supporting more bacterial species than a plain cabbage-and-salt ferment.
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; a fermented-food diet raised microbiota diversity over a 10-week trial.

How to choose

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

Common questions

Does cooking kill the probiotics?: Yes, sustained heat kills the bacteria; lactic acid bacteria stop growing above about 45 C and are progressively killed at cooking and pasteurisation temperatures. 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?: Pasteurised (shelf-stable) sauerkraut is the safer choice in pregnancy. Unpasteurised live sauerkraut, including refrigerated and homemade jars, is best avoided, because Listeria can grow even at fridge temperatures and pregnancy raises the risk of serious infection. If in doubt, cook it until steaming hot or check with your midwife.
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

Lactic Acid Fermentations, sauerkraut microbiology, salt level and LAB sequence (Applications of Biotechnology to Fermented Foods, NRC) (National Academies Press / NCBI Bookshelf)
Gut-microbiota-targeted diets modulate human immune status (fermented-food diet increased microbiota diversity, 10-week intervention), Wastyk 2021 (Cell (PMID 34256014))
Fermented foods food fact sheet (sauerkraut as a source of probiotics, fibre and iron) (British Dietetic Association)
Bioactive Properties, Volatile Compounds, and Sensory Profile of Sauerkraut (isothiocyanates from glucosinolate hydrolysis), 2022 (Foods / NCBI PMC)
Influence of fermentation on glucosinolates and glucobrassicin degradation products in sauerkraut (glucosinolates degraded by Day 7), Ciska 2015 (Food Chemistry (PMID 26213035))
Sauerkraut, canned, solids and liquids, energy, vitamin C, vitamin K, fibre, sodium (USDA Standard Reference) (USDA National Nutrient Database (via NutritionValue.org))
Metagenomic Analysis of Kimchi (kimchi dominated by ~6 to 11 lactic acid bacteria species) (Applied and Environmental Microbiology / NCBI PMC)
Quantifying Variability in Growth and Thermal Inactivation Kinetics of Lactobacillus plantarum (thermal death at 55–63 C) (Applied and Environmental Microbiology / NCBI PMC)
An Update Review on Listeria Infection in Pregnancy (Listeria grows at -0.4 to 45 C; pregnant women 18x higher risk) (NCBI PMC)
Listeriosis, foods to avoid in pregnancy including unpasteurised products (NHS)