Fermented Foods: Kimchi, Sauerkraut and More

What Is Fermentation?

Fermentation is an ancient food preservation process in which microorganisms such as bacteria, yeasts, or moulds break down organic compounds. The most common form is lactic acid fermentation (lactofermentation). In this process, lactic acid bacteria convert sugars into lactic acid. This lowers the pH of the food and makes it shelf-stable, because harmful pathogens cannot multiply in the acidic environment.

Lactic acid fermentation has been used for thousands of years. Sauerkraut has been documented in Europe since the Middle Ages, and kimchi in Korea for over 2,000 years. What began as a preservation method is now at the centre of nutrition research, because fermented foods contain living microorganisms that may positively influence the gut microbiome.

An Overview of Fermented Foods

The variety of fermented foods is vast. Every culture has its own traditions:

Food	Origin	Base Ingredient	Dominant Cultures
Sauerkraut	Europe	White cabbage	Lactobacillus plantarum, L. brevis
Kimchi	Korea	Napa cabbage, radish	Lactobacillus, Leuconostoc
Kefir	Caucasus	Milk	Lactobacillus, Saccharomyces
Kombucha	East Asia	Sweetened tea	Acetobacter, Saccharomyces
Miso	Japan	Soybeans, rice	Aspergillus oryzae
Tempeh	Indonesia	Soybeans	Rhizopus oligosporus
Yoghurt	Central Asia	Milk	L. bulgaricus, S. thermophilus

Important: not all fermented foods still contain living cultures. Beer, wine, and sourdough bread undergo fermentation, but the microorganisms are killed through heating or filtration.

Probiotic Cultures: Lactobacillus and Bifidobacterium

Two genera dominate the research on fermented foods:

Lactobacillus is the genus most commonly found in fermented foods. Various species (L. plantarum, L. rhamnosus, L. acidophilus) have been associated in studies with positive effects on the gut barrier and the immune system (Marco et al., 2017). Lactobacilli are particularly resistant to the acidic environment in the stomach and can reach the intestine alive.

Bifidobacterium occurs naturally in the human gut and is supplied through fermented dairy products such as yoghurt and kefir. Bifidobacteria produce short-chain fatty acids, particularly acetate and lactate, which serve as fuel for other beneficial gut bacteria.

A review by Marco et al. (2017) in Current Opinion in Biotechnology summarised that fermented foods can increase microbial diversity in the gut because they deliver not only probiotic organisms but also metabolites such as organic acids, peptides, and vitamins that support the existing microbiome.

The Stanford Study: A Research Milestone

A widely cited study by Wastyk et al. (2021), conducted at Stanford School of Medicine and published in Cell, compared two dietary interventions over 10 weeks in 36 healthy adults:

• Group 1: Increased their consumption of fermented foods to 6 servings per day (yoghurt, kefir, kimchi, sauerkraut, kombucha).
• Group 2: Increased their fibre intake to over 40 g per day.

The results were remarkably clear. The fermented-foods group showed significantly higher microbiome diversity. In addition, 19 inflammatory markers in the blood were reduced, including interleukin-6 and interleukin-12. The fibre group, by contrast, showed no comparable increase in diversity, although the composition of the microbiome did change.

This does not mean that fibre is unimportant. However, the study suggests that fermented foods may have an independent and particularly strong effect on microbial diversity. The combination of both strategies is likely the most effective approach.

Histamine Intolerance: When Caution Is Needed

Fermented foods are not equally well tolerated by everyone. The fermentation process produces biogenic amines, particularly histamine. Individuals with histamine intolerance may develop symptoms such as headaches, skin rashes, or digestive complaints after consuming sauerkraut, kimchi, aged cheese, or red wine.

Dimidi et al. (2019) noted in a review in Alimentary Pharmacology & Therapeutics that while the evidence for health benefits of fermented foods is promising, individual tolerance must be taken into account. Anyone who regularly experiences discomfort after eating fermented foods should seek medical advice.

Not all fermented foods contain the same amount of histamine. Fresh yoghurt and kefir are generally better tolerated than products that have been aged for a long time, such as sauerkraut or kombucha.

Fermented vs. Pasteurised: What to Look for When Buying

Many commercially available fermented products are pasteurised after fermentation. This kills the living cultures through heating. It extends shelf life but eliminates the probiotic benefit.

What to look for:

• Refrigerated section, not the shelf: Unpasteurised products are found in the refrigerated section. Sauerkraut in tins or jars stored at room temperature is almost always pasteurised.
• Check the ingredients list: Does the product contain vinegar instead of natural acidity? Then it was not fermented but pickled in vinegar.
• Label claims: Terms such as “raw”, “unpasteurised”, “with live cultures”, or “naturally fermented” indicate a product that has not been heat-treated.
• Make your own: Sauerkraut and kimchi can be made at home with minimal effort. All you need is vegetables, salt, and a jar.

Practical Tips: Integrating Fermented Foods into Daily Life

The Stanford study used 6 servings of fermented foods per day. That is an ambitious target. For beginners, smaller amounts that can be gradually increased are a good starting point.

• Morning: Natural yoghurt or kefir for breakfast. Combine with oats, nuts, and fruit.
• Lunch: 2-3 tablespoons of sauerkraut or kimchi as a side dish. Goes well with rice, salads, or bowls.
• Evening: Miso soup as a starter. Dissolve miso paste in warm (not boiling) water to preserve the cultures.
• Between meals: A small glass of kombucha or water kefir as an alternative to sugary drinks.

Important: fermented foods should not be heated, because high temperatures kill the living cultures. When adding sauerkraut as a side dish, add it after cooking rather than during.

Conclusion

Fermented foods combine a tradition spanning thousands of years with modern nutrition research. The Stanford study by Wastyk et al. (2021) provides strong evidence that regular consumption may increase microbiome diversity and reduce inflammatory markers. Quality is key: only unpasteurised products with living cultures deliver probiotic benefits. Gradually integrating fermented foods into everyday meals is a simple and enjoyable way to support gut health.

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Sources:

• Wastyk HC et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137-4153.
• Marco ML et al. (2017). Health benefits of fermented foods: microbiota and beyond. Current Opinion in Biotechnology, 44, 94-102.
• Dimidi E et al. (2019). Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease. Alimentary Pharmacology & Therapeutics, 51(8), 982-1000.