Hello forum, I am trying to determine the optimal pH for L. reuteri yogurt, and I keep reading contradicting information. Many on YouTube recommend 4.5-4.0 pH. Some say L. reuteri will die below that. Some have said that fermenting until 3.5 to 3.0 pH maximizes L. reuteri count. Some say stop the ferment right when the yogurt sets. I am under the impression that allowing some additional fermentation time after the yogurt sets will increase bacterial count (if kept within optimal pH range). Is this true? What pH should you stop fermenting using the NPSelection Reuteri and Salivarius starter? Thank you!
The question about the ideal pH for L. reuteri yogurt can be confusing because different sources are aiming for different results. Some people focus on getting the lowest possible lactose, others want a very thick yogurt, and some try to maximise bacteria without considering which bacteria actually survive. When all these goals are combined, the advice starts to contradict itself.
If we look at the culture itself, the picture becomes clearer. A blend like NPSelection includes Lactobacillus reuteri and Lactobacillus salivarius together with traditional yogurt bacteria such as Lactobacillus bulgaricus and Streptococcus thermophilus. These do not behave the same way. The classic yogurt bacteria are more acid-tolerant and can continue working at lower pH. In contrast, L. reuteri and L. salivarius are more sensitive and start to slow down earlier.
This explains why very low pH values, like 3.5 or even 3.0, are not ideal. At that point, fermentation is still happening, but mostly driven by the acid-tolerant bacteria. The more sensitive strains gradually decline. So while the total number of bacteria might still be high, the balance of the culture changes, and you lose part of what you were aiming for.
At the same time, it is not correct to say that L. reuteri suddenly dies below a certain pH, like 4.5. The process is gradual. As the pH drops, the bacteria slow down, then stop growing, and only later begin to die off if they stay in that environment. Both pH and time matter.
In practice, yogurt usually sets at around pH 4.8 to 5.0. Letting it ferment a bit longer after it sets is beneficial. It improves texture, further reduces lactose, and allows the culture to develop. However, this should be done within limits.
The most balanced pH range for a mixed culture like this is 4.4 to 4.5. At this level, the yogurt has a good structure and mild taste, and all the bacteria are still present in good numbers. If fermentation continues much further, the system shifts, and the acid-tolerant species take over.
So yes, allowing some extra fermentation after the yogurt sets is useful, but the key is not time—it is the pH. For the NPSelection Reuteri and Salivarius starter, the best approach is to stop fermentation at about pH 4.4–4.5 and cool it down immediately. This keeps the culture balanced and preserves the diversity you are trying to achieve.
Thank you very much for this, I just finished a batch of the l reuteri and l salivarius that measured pH around 4.0 after 14 hours and it’s perfect taste and consistency. Very helpful info. For purposes of repopulating the microbiome, is there a recommended amount of yogurt to have daily? I know everyone is different, it’s just so good that I could easily eat too much lol
The question of how much homemade yogurt to consume for supporting the microbiome is a natural one, especially when the result is both enjoyable and well-fermented, as in your case. A batch reaching around pH 4.0 after approximately 14 hours suggests a well-balanced fermentation, where both taste and texture align with what we would expect from an active culture. This already indicates that the process has worked in harmony with the milk and environment, producing a food that is both nutritionally and microbiologically rich.
When considering daily intake, it is important to move away from the idea that larger quantities necessarily bring greater benefit. The human microbiome does not respond in a simple linear way to the amount of a single food. Instead, it behaves more like an ecosystem—dynamic, adaptive, and dependent on balance. In this context, smaller and more frequent servings are generally more supportive than consuming large amounts at once. A practical and effective approach is to consume one to three spoonfuls, two to three times per day. This allows for regular exposure without overwhelming the system, supporting gradual and sustainable interaction with existing microbial populations.
An interesting and often overlooked aspect is that plain yogurt, when left unaltered, tends to regulate intake naturally. As a balanced food—containing proteins, fats, and fermentation-derived compounds—it provides internal signals of satiety. Most people find that when consuming it without added sugar or flavourings, the body intuitively indicates when enough has been consumed. However, once sugar or other additives are introduced, this balance is disrupted. The product becomes easier to overconsume, not because the body needs more, but because the natural feedback mechanisms are overridden.
Equally important is the recognition that no single strain or even a specific combination of bacteria can define a healthy microbiome. Diversity remains the central principle. For this reason, yogurt should be seen as one component within a broader dietary pattern. Including a range of fermented foods—such as kefir, cheeses, and fermented vegetables like kimchi—introduces different microbial communities and metabolic byproducts, enriching the overall system. Alongside this, adequate intake of dietary fibre is essential, as it provides the substrates that these microbes rely on to thrive. At the same time, reducing sugar and highly processed foods helps maintain a more stable and favourable environment within the gut.
In the end, the goal is not to maximise the intake of a single “beneficial” food, but to cultivate balance, variety, and consistency. When approached in this way, even small amounts of well-prepared yogurt can contribute meaningfully to the broader objective of supporting a resilient and diverse microbiome.
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