What happens when cabbage ferments?

Sauerkraut is more than preserved cabbage. During fermentation, naturally occurring bacteria transform the cabbage, producing lactic acid and other compounds that help create its distinctive flavour, aroma and acidity.

What does the research tell us?

A 2022 study published in Frontiers in Microbiology investigated the microbial and chemical changes occurring during the fermentation of artisanal sauerkraut.

Researchers found that:

• Living bacteria drive fermentation. Lactic acid bacteria became dominant as fermentation progressed.

• Fermentation changes the chemistry of cabbage. Researchers identified changes in organic acids, amino acids and other metabolites throughout the process.

• Different fermentations produce different results. The two producers studied developed distinct microbial communities and chemical profiles.

• Sauerkraut may influence immune signalling. In laboratory experiments, sauerkraut brine altered inflammatory signalling in a model combining intestinal and immune cells.

What does this mean for gut health?

The findings offer insight into how fermentation transforms cabbage and why fermented foods are of scientific interest.

However, the study did not demonstrate improved intestinal barrier function, and its laboratory findings do not establish that eating sauerkraut produces the same effects in humans.

Further research is needed to understand how fermented foods and their microbial metabolites may influence human health.

The Fresh Ferments perspective

We believe good fermentation deserves to be understood, not simply celebrated.

By exploring the science behind traditional fermentation, we can better understand the microorganisms, acidity and chemical transformations that give fermented foods their distinctive character.

Traditional methods. Living processes. Science worth exploring.

Research source: Gaudioso, G. et al. (2022). Microbial and metabolic characterization of organic artisanal sauerkraut fermentation and study of gut health-promoting properties of sauerkraut brine. Frontiers in Microbiology, 13.

How do bacteria transform cabbage?

Sauerkraut fermentation is a natural process in which bacteria transform cabbage, producing acids and changing the availability of certain plant compounds. Scientists are discovering that this process is more complex than simply making cabbage sour.

What does the research tell us?

A 2022 study published in Microbiology Spectrum investigated how the bacterial community and chemical composition of sauerkraut changed over 42 days of fermentation.

Researchers found that:

• Different bacteria play different roles. The bacterial community changed as fermentation progressed, with different species becoming more prominent at different stages.

• Acidity increases. Lactic acid accumulated during fermentation, while the pH fell from approximately 5.9 to 3.4 under the study's conditions.

• Fermentation transforms plant compounds. Researchers observed changes in phenolic compounds, naturally occurring substances found in cabbage.

• Bacteria can alter these compounds. Some lactic acid bacteria appeared to have the ability to transform phenolic compounds into different substances, potentially affecting the characteristics of the finished sauerkraut.

• Less familiar bacteria may matter too. The study identified Secundilactobacillus malefermentans as part of the core bacterial community, particularly during the later stages of fermentation.

What are phenolic compounds?

Phenolic compounds are naturally occurring substances found in plants, including cabbage. They contribute to plant chemistry and can have antioxidant activity in certain experimental settings.

During fermentation, bacteria can help release these compounds from the plant material or transform them into different forms.

This means fermentation may change not only the flavour and acidity of cabbage, but also its chemical composition.

However, detecting changes in phenolic compounds does not automatically mean that the finished food provides a particular health benefit.

What does this mean for fermented foods?

The research helps explain why fermentation is a dynamic biological process. The bacteria present, the acidity and the chemical composition of sauerkraut all change over time.

Understanding these changes may eventually help researchers develop more consistent fermentation methods and investigate the potential nutritional properties of fermented vegetables.

The study examined sauerkraut fermented at 15°C for 42 days under specific experimental conditions. Its results cannot automatically be applied to every sauerkraut or fermentation method.

The Fresh Ferments perspective

We see fermentation as a meeting point between traditional food craft and microbiology.

By studying the microorganisms and chemical changes involved, scientists are building a clearer picture of how fermented foods develop their distinctive characteristics.

Traditional methods. Living processes. Science worth exploring.

Research source: Tlais, A. Z. et al. (2022). How Microbiome Composition Correlates with Biochemical Changes during Sauerkraut Fermentation: a Focus on Neglected Bacterial Players and Functionalities. Microbiology Spectrum, 10(4).

Can eating sauerkraut change the gut microbiome?

Fermentation changes cabbage before we eat it, but what happens after it reaches our digestive system? Scientists have begun investigating whether regular sauerkraut consumption influences the bacteria living in the human gut.

What does the research tell us?

A 2025 study published in Microbiome investigated the effects of eating fresh and pasteurised sauerkraut on the gut microbiome of 87 healthy adults.

Participants consumed 100 g of sauerkraut daily for four weeks during each intervention, with a break between the two phases.

Researchers found that:

• Some gut bacteria changed in abundance. Fresh sauerkraut consumption increased the relative abundance of Lacticaseibacillus paracasei, a bacterium found in the sauerkraut itself.

• The overall microbiome remained relatively stable. Neither fresh nor pasteurised sauerkraut produced a significant overall change in gut microbial diversity.

• Pasteurised sauerkraut also had measurable effects. Certain bacterial species changed in abundance even when the sauerkraut no longer contained living bacteria.

• Some metabolic markers changed. Pasteurised sauerkraut consumption was associated with increases in three short-chain fatty acids measured in blood serum: acetic, propionic and butyric acids.

• Individual responses varied. The effects on particular bacteria differed according to factors including participants' existing microbiomes and dietary characteristics.

What are short-chain fatty acids?

Short-chain fatty acids (SCFAs) are compounds produced when microorganisms break down certain nutrients, particularly dietary fibre.

They include acetate, propionate and butyrate, which play important roles in human physiology, including the interaction between gut microbes and the body.

The researchers found that blood levels of these compounds increased following the pasteurised sauerkraut intervention. However, the same increase was not observed after eating fresh sauerkraut.

This unexpected result highlights the complexity of food–microbiome interactions. The effects of a fermented food cannot necessarily be predicted simply by whether it contains living bacteria.

Does sauerkraut improve gut health?

The study provides evidence that regular sauerkraut consumption can influence the abundance of particular gut bacteria and may affect certain metabolic markers.

However, neither type of sauerkraut produced a significant overall change in the gut microbiome of these healthy participants. The study also found no significant changes in stool consistency, bowel movement frequency or stool pH.

Although the changes in blood metabolites are scientifically interesting, the researchers did not establish that they led to improved health outcomes.

Further research is needed to understand the long-term effects of sauerkraut consumption and why different fermented products may produce different responses.

The Fresh Ferments perspective

Fermentation does not stop when a jar is opened. The food's composition, the microorganisms it contains and the way it interacts with our digestive system are all part of a much bigger picture.

This research highlights an important distinction: living bacteria are one aspect of fermented foods, but the compounds produced during fermentation may also be relevant.

Understanding both helps us explore fermented foods through evidence rather than assumptions.

Traditional methods. Living processes. Science worth exploring.

Research source: Schropp, N. et al. (2025). The impact of regular sauerkraut consumption on the human gut microbiota: a crossover intervention trial. Microbiome, 13, Article 52.