Does Homemade Kefir Contain L. reuteri?

November 1, 2025 •

4 min read

While kefir grains are known to contain a vast diversity of beneficial bacteria, the presence of specific strains like L. reuteri is not guaranteed. The microbial composition of homemade kefir can vary significantly based on factors like the origin of the grains, fermentation temperature, and milk source. This natural variability means your homemade kefir might contain L. reuteri, but it is not a given.

Quick Summary

The specific bacterial makeup of homemade kefir is highly variable and depends on many factors, so it is not a reliable source of L. reuteri. In contrast, certain yogurts are specifically formulated to be rich in this particular probiotic strain. Homemade kefir contains a much wider and more diverse range of microbes, which can be beneficial in other ways.

Key Points

Inconsistent Presence: Homemade kefir may or may not contain L. reuteri because its microbial makeup is highly variable and depends on many factors.
Microbial Competition: The natural 'wild ferment' of homemade kefir means faster-growing microbes often outcompete L. reuteri, especially at the typical room temperature fermentation.
Temperature Discrepancy: L. reuteri requires a higher, controlled temperature (around 100°F) to thrive and multiply, while kefir grains ferment at a lower room temperature.
Separate Culturing: For a reliable dose of L. reuteri, it is better to make a specialized L. reuteri yogurt separately and consume it alongside your regular homemade kefir.
Benefits of Diversity: While not a guaranteed source of L. reuteri, homemade kefir is still a highly beneficial probiotic food due to its vast diversity of bacteria and yeasts, which commercial versions lack.
Commercial Variations: Some commercial kefirs do contain added L. reuteri, but they lack the full spectrum of probiotics found in traditional, grain-based homemade kefir.

Understanding the Microbial Ecosystem of Kefir

Kefir is a potent probiotic food renowned for its complex and diverse microbial composition. Unlike the starter cultures used for yogurt, which typically contain only a handful of specific bacterial strains, kefir is made using symbiotic colonies of bacteria and yeasts known as 'kefir grains'. These grains are not actual cereal grains but rather a gelatinous matrix of microbes that ferment milk into a tangy, effervescent drink. The specific cocktail of microbes in kefir grains can number anywhere from 50 to over 100 different species.

The Role of Kefir Grains and Environmental Factors

The diversity of homemade kefir is one of its greatest strengths but also why its exact composition is unpredictable. The specific strains present in a given batch of kefir are heavily influenced by several factors:

Origin of Kefir Grains: Grains passed down through generations or sourced from different geographical locations will have their own unique microbial heritage.
Fermentation Temperature: The temperature at which kefir ferments plays a crucial role in which microbes thrive. L. reuteri, for example, prefers a higher temperature (around 100°F or 37°C) to multiply, which is much warmer than the typical room temperature (68-76°F) used for culturing traditional kefir.
Milk Source and Additives: The type of milk (cow, goat, etc.) and the presence of prebiotic fibers can also influence the microbial balance.
Fermentation Duration: The length of time the kefir ferments can change the dominance of certain strains over others, as the microbial ecosystem shifts.

Why You Can't Count on Homemade Kefir for L. reuteri

The primary reason homemade kefir is an unreliable source of L. reuteri is the competition from other microbes. Kefir is a 'wild ferment' where a massive number of bacteria and yeasts are competing for resources. When cultured at room temperature, the faster-growing strains will likely outcompete L. reuteri, preventing it from reaching therapeutic levels. While some traditional kefir may contain L. reuteri, it is not a dominant or guaranteed species. In contrast, specific L. reuteri yogurts are made using a monoculture of selected strains under precisely controlled conditions to ensure a high concentration of the desired bacteria.

Can You Add L. reuteri to Homemade Kefir?

Some people attempt to enrich their homemade kefir by adding L. reuteri probiotic tablets. However, most experts advise against this approach. The higher culturing temperature required for L. reuteri would disrupt the natural balance of the kefir grains and potentially harm the diverse microbiota that thrives at lower temperatures. Culturing the bacteria separately and then mixing the finished products before consumption is a more effective strategy for incorporating both.

Homemade Kefir vs. L. reuteri Yogurt


Feature	Homemade Kefir (from grains)	L. reuteri Yogurt (specific strains)
Microbial Diversity	Very high, up to 100+ species of bacteria and yeasts.	Low, often just one or a few specific L. reuteri strains.
Primary Fermentation	Natural, wild ferment at room temperature (68-76°F).	Cultured under precise, warm temperatures (around 100°F).
Presence of L. reuteri	Not guaranteed and often not dominant.	Guaranteed and present in high concentrations.
Probiotic Potency	High diversity but variable quantity.	High concentration of specific, targeted strains.
Fermentation Starter	Reusable kefir grains.	Specific powdered starter or capsules.
Texture	Thinner, tangy, and sometimes effervescent due to yeast.	Thicker and more consistent, like traditional yogurt.

The Unique Benefits of Homemade Kefir

While lacking a high concentration of L. reuteri, homemade kefir offers a robust set of its own benefits. The rich variety of microbes, including bacteria like Lactobacillus kefiranofaciens, Lentilactobacillus kefiri, and various yeasts, provides a broad-spectrum probiotic support system. This diverse microbial community is associated with numerous health advantages, such as producing kefiran (a beneficial polysaccharide), potent antibacterial properties, and immune system support. The spontaneous, symbiotic nature of kefir's fermentation means that its benefits are not limited to a single strain but arise from the combined action of its complex microbial community.

The Bottom Line

For individuals seeking the specific therapeutic benefits of L. reuteri, relying on homemade kefir is a shot in the dark. The natural, wild fermentation process does not reliably produce therapeutic concentrations of this particular strain due to temperature requirements and microbial competition. A controlled culture of L. reuteri yogurt is a more direct and effective method. However, this does not diminish the immense value of homemade kefir. Its rich, diverse microbial ecosystem makes it a powerful and beneficial probiotic in its own right, offering a wide range of health advantages that commercial products often lack. For those wanting both, culturing them separately and consuming them together is the recommended approach.

Frequently Asked Questions

No, you cannot guarantee the presence of L. reuteri in homemade kefir. The microbial composition is dynamic and influenced by many environmental factors, and L. reuteri is not a dominant species in traditional kefir fermentation.

Adding a specific L. reuteri culture directly to your kefir grains is not recommended. The different temperature requirements and microbial competition mean the L. reuteri will likely be outcompeted by the established kefir grains, and the attempt could compromise the integrity of your grains.

The best approach is to culture L. reuteri yogurt and homemade kefir separately. You can then consume a portion of each to get the benefits of both the high L. reuteri concentration and the diverse probiotics of kefir.

Commercial kefirs are often made using powdered starter cultures containing specific, selected strains, which can include L. reuteri. Unlike grain-based homemade kefir, their composition is intentionally controlled and standardized.

Yes, homemade kefir made with real grains is far more diverse in its microbial content, including both bacteria and beneficial yeasts, which are often absent in commercial products. This broader spectrum of probiotics offers a wider array of potential health benefits.

Making L. reuteri yogurt requires a specific starter culture (often from capsules or a specialized kit), prebiotic fiber like inulin, and fermentation at a consistent temperature of around 100°F (37°C) for 36 hours.

Yes, they are fundamentally different. Grain-based kefir is a true symbiotic culture with dozens of microbes, while powder-started kefir uses only a few, selected strains and is more like a drinkable yogurt.