Does Fermented Milk Have L. reuteri? Understanding the Probiotic Content

December 6, 2025 •

3 min read

According to research, the presence of specific probiotic strains like L. reuteri in fermented foods is not guaranteed and often depends on the manufacturing process. This makes understanding the difference between standard fermented milk and specialized versions crucial for those seeking targeted health benefits.

Quick Summary

Not all fermented milk products naturally contain L. reuteri; specific cultures are usually added to achieve a therapeutic dose, and the quantity can vary greatly.

Key Points

Not all fermented milk is equal: Standard yogurt and kefir do not reliably contain therapeutic levels of L. reuteri; specialized starter cultures are required.
High-dose requires specific steps: Making L. reuteri fermented dairy involves a special process with specific starter strains, longer incubation (36 hours), and lower temperatures.
Prebiotics are key for multiplication: Prebiotic fibers like inulin must be added to the fermenting milk to significantly increase the probiotic count to therapeutic levels.
Strain specificity matters: Research on L. reuteri's health benefits is often tied to specific strains, such as ATCC PTA 6475 and DSM 17938, making careful culture selection important.
Reclassification of the name: The microbe is now officially called Limosilactobacillus reuteri, but the old name is still widely used on products and in common discussion.
Homemade vs. store-bought: To get a potent dose of L. reuteri, homemade fermented dairy is often the most cost-effective method compared to taking multiple daily probiotic tablets.

The Surprising Truth About L. reuteri in Fermented Milk

Many consumers turn to fermented milk products like yogurt and kefir as a source of probiotics, the beneficial bacteria that support a healthy gut microbiome. However, a common misconception is that all fermented milk products contain the same spectrum of bacteria. The reality is far more specific. When it comes to the powerful probiotic L. reuteri, its presence is not a given and is heavily dependent on how the fermented milk is produced. This article explores why standard fermented dairy often lacks this specific strain and how to ensure you're consuming fermented milk with L. reuteri.

Natural vs. Purposefully Added Probiotics

Fermented foods like kefir and sauerkraut are sometimes cited as natural sources of L. reuteri, but the concentrations and consistency are often unpredictable. The microflora in naturally fermented products can vary significantly depending on environmental factors and the specific starter culture used. For instance, traditional kefir grains contain a wide variety of yeasts and bacteria, and while some strains of L. reuteri may be present, they are not guaranteed to be at high enough concentrations to offer the specific, documented health benefits.

In contrast, purposefully adding specific, lab-grown strains of L. reuteri is the only reliable way to ensure a high and consistent count of this probiotic. This approach is commonly used in commercial probiotic supplements and for making specific homemade probiotic dairy. Manufacturers of these specialty products use specific strains, such as ATCC PTA 6475 and DSM 17938, which have been studied for their potential health effects.

How is high-dose L. reuteri fermented milk made?

Creating a fermented milk product rich in L. reuteri is a deliberate and distinct process from making conventional yogurt. It requires a specific protocol to encourage the growth of the desired bacterial strains to therapeutic levels. The key steps include:

Sourcing a specialized starter culture: Unlike standard yogurt cultures which contain L. bulgaricus and S. thermophilus, L. reuteri yogurt requires a starter culture with specific, high-potency strains.
Using prebiotic fiber: Prebiotic fibers like inulin or potato starch are often added to the milk to act as food for the L. reuteri bacteria, helping them to multiply dramatically.
Longer fermentation time: While traditional yogurt ferments for a few hours, L. reuteri fermented dairy is often incubated for 30-36 hours.
Lower incubation temperature: L. reuteri ferments optimally at a lower temperature (around 100°F or 37°C) than traditional yogurt cultures.

This meticulous process is necessary to achieve the high bacterial counts associated with therapeutic benefits, which are not present in standard fermented milk products.

Comparison of Fermented Milk Products


Feature	Standard Yogurt	Homemade L. reuteri Yogurt	Traditional Kefir
Contains L. reuteri?	No, not typically.	Yes, high therapeutic counts.	Possibly, but inconsistent and low counts.
Primary Cultures	L. bulgaricus, S. thermophilus	Specific L. reuteri strains (e.g., ATCC PTA 6475, DSM 17938).	Complex mix of bacteria and yeast.
Fermentation Time	Approximately 6-12 hours.	30-36 hours.	Around 24 hours.
Optimal Temp	Higher, around 106-115°F (41-46°C).	Lower, around 97-100°F (36-38°C).	Room temperature, or lower for slower ferment.
Required Additives	None, for plain yogurt.	Prebiotic fiber is recommended to feed the culture.	No additives needed for basic fermentation.
Texture	Smooth, thick, and creamy.	Can be thin or separated into curds and whey; often described as 'cheesy'.	Tangy, slightly bubbly consistency.

The Reclassification of L. reuteri

It is important to note that in 2020, scientists reclassified the Lactobacillus genus, and L. reuteri was officially renamed Limosilactobacillus reuteri. While the new name is more accurate, many product labels and health resources still use the original name. When looking for products or starter cultures, you may see either name, but they refer to the same beneficial microbe.

Conclusion

So, does fermented milk contain L. reuteri? The answer is not a simple 'yes' or 'no.' Standard, store-bought fermented milk products like yogurt and kefir are not reliable sources for this specific probiotic. High, therapeutic levels of L. reuteri are only found in products or homemade recipes where the strain has been specifically and intentionally added as a starter culture. For those looking to increase their intake of this particular probiotic, specialized homemade dairy or targeted probiotic supplements are the most effective routes. Understanding the distinctions in fermentation allows you to make informed decisions for your gut health goals.

Visit Revolution Fermentation for an example of a homemade L. reuteri yogurt recipe.

Frequently Asked Questions

No, you cannot reliably get L. reuteri from regular store-bought yogurt. Standard yogurt is fermented with other bacteria, primarily Lactobacillus bulgaricus and Streptococcus thermophilus, not L. reuteri.

Yes, they are the same bacteria. In 2020, the species was reclassified and renamed Limosilactobacillus reuteri, but the old name, Lactobacillus reuteri, is still commonly used.

Kefir can contain L. reuteri, but it is not a consistent or guaranteed source. The microbial composition of kefir varies widely, and it won't contain the high concentrations of specific strains found in targeted fermented dairy.

You will need a specific L. reuteri starter culture (e.g., specific BioGaia tablets), a prebiotic fiber like inulin or potato starch, and a yogurt maker that can maintain a consistent low temperature (around 100°F or 37°C) for 36 hours.

L. reuteri is a slower-growing bacterium and requires a longer fermentation time at a lower temperature than traditional yogurt cultures to proliferate to therapeutic levels. The specific strains also have different metabolic preferences.

It can be inconsistent and often separates into curds and whey, unlike smooth traditional yogurt. This separation is normal and does not mean the batch has failed; both parts contain the beneficial bacteria.

Yes, adding prebiotic fiber is highly recommended. It acts as a nutrient source that encourages the L. reuteri bacteria to grow and multiply exponentially during the long fermentation process.