In recent years, cardiologist Dr William Davis revolutionized home fermentation with his “L. Reuteri superfood yogurt,” which rapidly spread across health blogs and forums worldwide. Thousands of people now incubate milk for 36 hours, hoping to enhance oxytocin release, restore gut balance, and even stimulate hair growth. While the concept is inspired, many first batches fail, and later “successes” often are not true L. Reuteri cultures at all—rather, mixed ferments dominated by faster lactic species that overtake the jar.
Dr Tsilikas, a medical doctor and psychiatrist, developed an improved method based on fundamental microbiological principles to make the culture more authentic, safer, and reproducible.
Why Many L. Reuteri Batches Fail
Dr Davis’ method instructs users to:
- mix crushed probiotic capsules directly into milk
- add some inulin, and
- incubate at 37–40 °C for 36 hours
The issue is biological. L. Reuteri is a slow and fragile organism that requires a slightly acidic environment to establish dominance. In milk with a neutral pH (~6.7), the conditions are too mild to suppress competing bacteria, allowing ordinary lactic acid species—or even stray environmental microbes—to multiply far more rapidly. By the time L. Reuteri begins to awaken, the neutral pH environment has already favored faster acidifiers, and another species may have taken over the jar.
The Scientific Fix: Give Reuteri a Head Start
Two microbiological refinements correct these weaknesses:
- Starter Activation Stage – gently rehydrate freeze-dried bacteria in warm milk (37 °C) with a touch of inulin before any acid exposure.
- Controlled Pre-acidification of Bulk Milk – lower the main batch’s pH slightly (to ≈ 5.8) using lemon juice or vinegar to restrain contaminants while allowing L. Reuteri to thrive.
Together, these measures let the correct organism dominate from the outset.
Step-by-Step Protocol
🔹 Step 1 – Starter Activation (Without Acidification – Jar #1)
Use a small, separate sterilized jar.
- Warm 100 ml of the milk type recommended in Dr Davis’s original recipe to 37 °C
- Add 2–4 capsules of L. Reuteri (DSM 17938 or similar)
- Add ½ teaspoon inulin and stir gently
- Let sit 15–20 minutes at 37 °C to rehydrate and wake the culture
Do not acidify Jar #1 — this neutral environment ensures gentle revival and enzyme activation.
🔹 Step 2 – Prepare Bulk Milk (With Acidification – Jar #2)
In a larger, separate jar, prepare the main fermentation medium.
- Warm 900 ml of the milk type recommended in Dr Davis’s original recipe to 37 °C
- Stir in 1 tablespoon inulin.
- Add ≈ 2 teaspoons lemon juice (or 1½ tsp vinegar).
- Mix and taste: lightly tart, not sour. Target pH ≈ 5.7–5.9
Jar #2 is intentionally acidified to suppress unwanted microbes and favor L. Reuteri.
🔹 Step 3 – Combine (Both Jars)
- Pour the activated starter from Jar #1 into the acidified milk in Jar #2.
- Stir slowly to distribute evenly without frothing or oxygenation.
🔹 Step 4 – Ferment
- Incubate the combined jar at 37–38 °C for 30–36 hours.
- Keep the lid loose to permit minimal gas release.
- Do not stir during fermentation.
🔹 Step 5 – Finish
Expect a thin, mild yogurt with some whey separation — normal for L. Reuteri.
- Refrigerate immediately after completion to preserve viability.
- Retain 2–3 tablespoons as starter for up to two further batches, then restart from capsules to prevent strain drift.
Maintenance and Re-Use of the Culture
Once your first fermentation has completed successfully, you may preserve part of it as a living starter for future batches. This allows the L. Reuteri population to remain active and eliminates the need to open new probiotic capsules each time—provided purity and stability are maintained.
🔹 When a Batch Is Eligible for Re-Use
Only reuse the yogurt if it clearly demonstrates that L. Reuteri was the dominant organism. You can verify this through the following simple criteria:
| Parameter | Healthy L. Reuteri Yogurt | Meaning |
| Incubation time | Full 30–36 h at ~37 °C | Ensures high viable count (10⁸–10⁹ CFU/ml) |
| Texture | Thin, slightly separated, not thick or rubbery | Indicates slow acidifier characteristic of L. Reuteri |
| Aroma / taste | Mild, buttery, lightly sweet, not sharply sour | Confirms absence of aggressive acid-formers |
| Final pH | 4.4 – 4.8 | Typical endpoint for L. Reuteri |
| Surface | Clean, no bubbles or slime | Free of yeasts or contaminants |
If all of these conditions are met, the jar can safely serve as the inoculum for your next preparation.
🔹 How to Harvest and Store the Starter
Immediately after incubation ends — before refrigeration — stir the yogurt gently to homogenize.
- Using a sterilized spoon, transfer 2–3 tablespoons of the fresh yogurt into a clean, dry jar.
- Close the jar and refrigerate promptly at 4 °C.
- Use this stored starter within 7 days to begin your next batch.
🔹 How Many Generations to Re-Use
For optimal strain fidelity:
- Re-use the starter for no more than 2–3 consecutive batches.
- After that, restart the culture from fresh capsules to avoid genetic drift or silent contamination by faster lactic species.
🔹 Quick “Go / No-Go” Reference
| Observation | Re-use? | Interpretation |
| Mild taste, thin texture | ✅ Yes | True L. Reuteri profile |
| Thick, tangy, strong acid smell | ❌ No | Likely takeover by L. bulgaricus / L. casei |
| Bubbles, slime, or surface film | ❌ No | Contaminated by yeast or other microbes |
| Stored > 7 days in fridge | ⚠️ Not recommended | Viability drops markedly |
🔹 Summary
You may reserve 2–3 tablespoons of the previous batch immediately after fermentation, provided the yogurt is mild, clean, and consistent with the L. Reuteri phenotype.
Use that inoculum within a week, repeat this for up to three cycles, and then return to a capsule-based starter to maintain the integrity of your culture.
Why This Protocol Is Superior
| Potential Issues in Dr Davis’s Recipe | Dr Tsilikas’s Enhancement | Benefit for Microbial Integrity |
| Cold milk shocks freeze-dried cells | Warm activation in Jar #1 | Maximizes initial viability and growth |
| Neutral pH (≈ 6.7) favors contaminants | Pre-acidify bulk milk to ≈ 5.8 in Jar #2 | Selectively favors L. Reuteri over competitors |
| No adaptation phase | Two-jar staged process | Controlled environment and reproducibility |
| Random success after 1–2 weeks | Defined parameters from start | Predictable texture and strain purity |
Interpreting Your Results
- Mild taste + thin texture = authentic L. Reuteri.
- Fast thickening or sharp tang = contamination (by L. bulgaricus, L. casei, etc.).
- Maintain sterility and limit starter reuse to preserve strain identity.
Final Remarks — When Fermentation Meets Clinical Microbiology
Dr Davis deserves recognition for bringing L. Reuteri to public attention.
This refined, evidence-based version — the Dr Tsilikas Nikolaos Two-Jar L. Reuteri Protocol — separates revival from acidification to achieve a stable, lab-grade ferment under home conditions. The outcome is a culture truer to the intended strain, with higher viability, lower failure rates, and greater consistency across batches.
If your goal is to cultivate authentic L. Reuteri and not merely any lactic acid bacterium, this protocol is a sound way to do so.
Disclaimer — For educational purposes only. Not a substitute for medical advice. Always maintain hygienic equipment and food-safety standards during fermentation.
If you require additional information on this topic, feel free to explore our article about Dr. William Davis’s L. Reuteri Yogurt: Science, Benefits and Potential.
