What Probiotics Are in Kefir? Your Guide to Its Diverse Microbes

November 16, 2025 •

4 min read

Kefir grains can contain up to 60 unique species of bacteria and yeast, creating a profoundly diverse probiotic profile. This richness is why many health enthusiasts wonder what probiotics are in kefir and how these microbes benefit gut health.

Quick Summary

Kefir's diverse probiotic profile stems from its symbiotic culture of bacteria and yeasts, known as kefir grains. This includes multiple species of Lactobacillus, Lactococcus, Bifidobacterium, and beneficial yeasts.

Key Points

Rich Diversity: Kefir contains a far wider array of beneficial bacteria and yeasts, with up to 60 unique species identified in some grains.
Unique Grains: The probiotic content comes from kefir grains, a symbiotic culture of bacteria and yeast, not starter cultures, which delivers greater microbial diversity.
Key Strains: A crucial probiotic in kefir is Lactobacillus kefiri, known for its antimicrobial properties against harmful pathogens.
More Probiotics than Yogurt: Kefir typically contains a higher quantity and greater diversity of colony-forming units (CFUs) than yogurt, sometimes featuring a mix of beneficial yeasts as well.
Lactose-Friendly: The fermentation process significantly reduces lactose content, making kefir more digestible for many individuals with lactose intolerance.
Influential Factors: The specific probiotics in kefir can vary based on the grains' origin, fermentation time and temperature, and whether it is homemade or commercially produced.

A Complex Ecosystem: The Microbiome of Kefir

At the heart of kefir's rich probiotic content lies the kefir grain—a symbiotic culture of bacteria and yeasts (SCOBY). These unique, cauliflower-like structures are not actual cereal grains but living microbial colonies encased in a complex polysaccharide matrix called kefiran. It is this intricate community that differentiates kefir from other fermented products like yogurt, delivering a far greater diversity and number of beneficial microorganisms. The specific microbial composition can vary based on the grains' origin, the type of milk or sugar water used, and fermentation conditions, but certain species are consistently present.

The Key Bacterial Families in Kefir

The bacteria in kefir primarily belong to lactic acid bacteria (LAB) and acetic acid bacteria (AAB), which are responsible for fermenting the milk's lactose or sugar water. This process produces lactic acid, carbon dioxide, and other compounds that give kefir its characteristic tangy, slightly effervescent flavor. Key bacterial species often found include:

Lactobacillus species: This genus is a cornerstone of kefir's probiotic profile. Important species include Lactobacillus kefiri, which is unique to kefir grains and known for its antimicrobial properties against pathogens like E. coli and Salmonella. Other common strains are Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus helveticus.
Lactococcus species: These bacteria, particularly Lactococcus lactis, are important for initiating fermentation and contributing to the product's flavor.
Streptococcus species: Streptococcus thermophilus is a well-known bacterium often present in kefir, though typically more associated with yogurt.
Leuconostoc species: These bacteria also play a role in creating kefir's distinctive flavor profile and are a common component of the kefir grain ecosystem.
Bifidobacterium species: A genus highly valued for its health benefits, including supporting digestion and immunity. Strains like Bifidobacterium bifidum and Bifidobacterium lactis are frequently identified in kefir.

The Role of Yeasts in Kefir

Unlike most yogurts, kefir contains a population of beneficial yeasts in addition to bacteria, which contribute to its unique properties and effervescence. These yeasts help in the fermentation process and offer their own range of potential health benefits. Common yeasts include:

Saccharomyces cerevisiae: A well-known yeast strain also used in baking and brewing, found in both milk and water kefir.
Kluyveromyces marxianus: This yeast ferments lactose and contributes to kefir's flavor and texture.
Candida kefyr: A lactose-fermenting yeast that is a defining component of kefir grains.

Milk Kefir vs. Water Kefir

The probiotic composition of kefir varies significantly depending on the fermentation base. Milk kefir, made with dairy, contains bacteria that thrive on lactose, while water kefir, made with a sugar water solution, has a different microbial community. While milk kefir generally offers a broader spectrum of microorganisms, both types deliver a significant boost of diverse probiotics compared to many other fermented foods.

Factors Affecting Kefir's Probiotic Content

Several factors can influence the final probiotic makeup of kefir, even when using the same grain source. Understanding these variables helps in optimizing the final product for specific health goals:

Grain Origin and Maintenance: The geographical origin and how kefir grains are maintained will cause natural variations in their microbial community.
Fermentation Duration and Temperature: Longer fermentation times at warmer temperatures can increase the number of probiotics, as the microbes have more time to multiply.
Substrate (Milk Type): Different milks (cow, goat, sheep) and fermentation bases (sugar water) provide varying nutrient levels, which can favor the growth of certain microbial strains over others.
Commercial vs. Homemade: Some commercial kefirs use isolated starter cultures instead of true kefir grains, which results in a less diverse probiotic profile than homemade kefir.

Comparison: Kefir vs. Yogurt Probiotics


Feature	Kefir	Yogurt	Comparison Notes
Microbial Diversity	High, often containing up to 60 species of bacteria and yeast.	Lower, typically containing 1-5 species of bacteria.	Kefir's symbiotic culture delivers a much broader range of microorganisms.
CFU Count	Very high, with some brands boasting 25-50 billion CFU per cup.	Variable, with an average of around 6 billion CFU.	Kefir consistently offers a higher quantity of colony-forming units.
Microbe Types	Contains a mix of bacteria and beneficial yeasts.	Primarily contains bacteria.	The presence of yeasts is a unique characteristic of kefir.
Digestion	The longer fermentation process breaks down lactose more completely, making it up to 99% lactose-free and easier to digest for many with lactose intolerance.	Varies, but generally contains more lactose than kefir.	Kefir is often a better option for those with lactose sensitivity.
Bioactive Compounds	Produces a wider array of bioactive peptides and compounds during fermentation due to the varied microbial activity.	Produces fewer bioactive compounds due to a less diverse microbial profile.	Kefir's complex fermentation results in a greater range of beneficial byproducts.

Conclusion: More Than Just a Probiotic Drink

Kefir stands out as an exceptional source of probiotics due to the profound diversity of its microbial ecosystem, which includes a wide range of bacteria and yeasts derived from its unique kefir grains. Unlike many yogurts with a limited number of strains, kefir provides a broad spectrum of beneficial microorganisms, like Lactobacillus kefiri and Bifidobacterium species, that contribute to a healthy gut microbiome. This microbial richness, combined with the production of bioactive compounds during fermentation, offers a robust approach to supporting digestive and overall health. For those seeking to boost their intake of beneficial microbes, understanding what probiotics are in kefir confirms its status as a potent and beneficial fermented food. To learn more about kefir's comprehensive health benefits, consult authoritative research like this study from the National Institutes of Health.

Frequently Asked Questions

While kefir contains a vast array of microbes, a distinguishing probiotic is Lactobacillus kefiri, a strain that is unique to the kefir grain ecosystem and is known for its ability to fight off harmful bacteria.

Yes, kefir is widely considered a superior source of probiotics compared to most yogurts. It typically contains a much greater diversity of bacteria and yeasts, often with a higher concentration of colony-forming units (CFUs) per serving.

Milk kefir is made using kefir grains and milk, while water kefir is made with water kefir grains and sugar water. Their probiotic composition differs, with milk kefir typically having greater microbial diversity, though both are excellent probiotic sources.

Not all commercially produced kefir guarantees the same level of probiotic diversity or viability. Some brands use isolated starter cultures rather than traditional kefir grains. Look for labels that specify "live and active cultures" to ensure you are getting the probiotic benefits.

Despite their name, kefir grains are not actual cereal grains but small, gelatinous, cauliflower-like colonies of bacteria and yeasts. This symbiotic culture (SCOBY) is what is used to ferment milk or sugar water to create kefir.

Yes, many individuals with lactose intolerance can consume milk kefir without issues. The bacteria in kefir grains consume a significant portion of the lactose during fermentation, making it up to 99% lactose-free and easier to digest.

Kefir contains several beneficial yeasts, including Saccharomyces cerevisiae, Kluyveromyces marxianus, and Candida kefyr. These contribute to the tangy flavor, light carbonation, and the overall probiotic benefits.