If your kefir grains are not multiplying, it rarely means the culture is bad. Most often, temperature, the milk, the grain-to-milk ratio or small care habits are slowing growth down, and these are easy to fix.

Are your kefir grains really not multiplying?

If your kefir grains are not multiplying visibly, the first step is to find out whether they are really not growing or whether the change is simply hard to see. Kefir grains stick together, form larger clusters and then break apart again, so it is very difficult to judge by eye whether you have more than before.

The most reliable method is weighing. Once a week, when you strain your kefir, put the drained grains on a kitchen scale and note their weight. Two or three weeks of data tell you far more than any visual estimate. Scientific studies work the same way: they track kefir grain biomass on a scale over repeated fermentation cycles.

If your kefir grains:

look healthy (white or cream-coloured, elastic),
regularly thicken and sour the milk,
produce kefir with a characteristic, pleasantly tangy smell,
show no signs of mould or spoilage,

then the culture is working. In that case, slow multiplication comes from the conditions or the culture itself, and in most cases it can be improved with simple changes.

What affects kefir grain growth?

1. Temperature

Temperature is one of the most important factors, because it affects both the activity of the bacteria and yeasts and the speed of fermentation.

Research shows its impact clearly. In a study of kefir grain biomass growth, cultivation conditions, including temperature, had a significant influence on how much the grains increased. A 2025 study using household kefir grains found 25 °C to be the optimal fermentation temperature, without agitation and with a relatively small initial amount of grains. This result applies to that particular culture and experimental system, but it fits well with the proven 20–25 °C range for homemade kefir.

A persistently cool kitchen (an unheated pantry or windowsill in winter) slows fermentation and, with it, grain growth. Persistent heat, for example near a radiator or oven in summer, is also unfavourable, because overly fast, overly acidic fermentation puts the culture under strain.

What to do: keep your kefir grains in a stable spot at around 20–25 °C, away from direct sunlight and heat sources, and avoid large temperature fluctuations.

2. The milk

For kefir grains, milk is not just a liquid; it is the food they build themselves from. The composition of the milk therefore shapes not only fermentation but also the structure of the grains.

A 2026 study followed how kefir grains develop in different milk-based media over 28 days of continuous subculturing. In cow's milk, compact and stable grains formed; in goat's milk, a looser, more filamentous structure rich in polysaccharides; and in whey protein concentrate, fragmented grains. In other words, the type of milk directly influences what your kefir grains become.

If your grains used to grow well but slowed down after a change of milk, the new milk may be the cause.

What to do: use good-quality cow's milk, and once a milk has worked well, stick with it. If you switch to a new milk, give the culture a few cycles to adapt before drawing conclusions.

3. The grain-to-milk ratio

A common misconception is that adding more grains to the milk will make them multiply faster. In reality, a lot of grains in a little milk use up the nutrients quickly, the milk becomes overly sour, and the grains spend most of the cycle in an unfavourable, highly acidic environment.

Interestingly, in the 2025 study mentioned above, a relatively small initial amount of grains (5 g per litre) was part of the optimal conditions. That does not mean you should use this amount at home, but it shows clearly that more grains are not necessarily better.

What to do: as a starting point, about 1 tablespoon of grains in 200–300 ml of milk is a well-proven ratio. As the grains grow, increase the amount of milk or remove some of the grains. We describe the exact steps in our guide to making homemade kefir.

4. Fermenting too long and changing the milk too rarely

During fermentation, the microorganisms consume nutrients and produce acids and other metabolites, so the environment becomes increasingly acidic and nutrient-poor. If the grains regularly stay in the same milk much longer than it takes for the kefir to be ready, they spend the end of each cycle in a hungry, stressed state.

The situation is similar if the grains sit in the fridge for weeks. The cold slows the culture down, and afterwards it takes time for it to regain its usual activity. The occasional long fermentation or short rest in the fridge is not a problem, but if it becomes the routine, it shows in the growth.

What to do: change the milk regularly, ideally every day once the kefir is ready. If you resume after a break of a few days, expect the grains to need a few cycles to get back up to speed.

5. Washing too often and handling roughly

You do not need to wash kefir grains after every straining. Unnecessary rinsing can wash a useful part of the culture off the surface of the grains, which slows growth. Pressing, rubbing or forcing the grains through the strainer with a spoon is just as harmful.

What to do: after straining, put the grains straight into fresh milk without washing them. If you do need to rinse them for some reason, use clean, cold water and return the grains to milk as soon as possible. When straining, only stir the kefir gently in the strainer.

6. Time to adapt

Freshly purchased grains that have arrived by post, or a culture whose conditions have suddenly changed (different milk, temperature or fermentation rhythm), will not work at full strength straight away. Fermentation may be slower in the first few days, and growth even more so.

What to do: for the first two to three weeks, provide stable conditions and do not change several things at once. If you change the milk, temperature, ratio and fermentation time all at the same time, it becomes impossible to tell what helped and what hurt.

7. The culture itself

Kefir grains are a complex community of bacteria and yeasts held together by a polysaccharide-rich matrix. Cultures of different origins differ in their microbial composition and fermentation properties, so two healthy kefir cultures may grow at different rates even with the same care. We explain this in more detail in our article on Tibetan kefir grains.

Slower growth alone therefore does not prove that your grains are of poor quality. If they make good kefir, the culture is healthy.

How can you help your kefir grains multiply?

If your grains are healthy but have barely grown for weeks, these steps will give them the best conditions for growth:

Keep them in a stable spot at around 20–25 °C, away from heat sources and cold windowsills.
Use good-quality cow's milk, and once a milk has worked, do not change it unnecessarily.
Watch the ratio: the grains should always have plenty of milk, about 1 tablespoon of grains in 200–300 ml of milk to start with.
Change the milk regularly once the kefir is ready, and do not let it over-ferment as a routine.
Do not wash the grains unnecessarily, and handle them gently when straining.
Change only one thing at a time, and observe the effect for a few cycles.
Weigh the grains weekly to get a realistic picture of their growth.

In most cases, these steps visibly improve growth within a few weeks. Keep in mind, though, that faster souring is not the same as faster multiplication. The goal is stable, healthy activity, not the fastest possible fermentation.

How long should it take for kefir grains to multiply?

There is no single number that applies to every culture. What is certain is that growth is best measured in weeks, not in individual batches. Research also tracks kefir grain biomass over several weeks and many consecutive cycles, and the rate of growth depends on temperature, milk, initial amount and the culture itself.

So do not expect your kefir grains to be visibly larger after every fermentation. For a healthy culture, it is far more telling whether its weight gradually increases over two or three weeks of weekly weighing, and whether it keeps making good kefir in the meantime.

When should you suspect a real problem?

Slow growth and real damage to the culture are two different things. Pay attention if you notice any of the following:

coloured, fuzzy spots on the grains or on the surface of the kefir that suggest mould,
an unusual, unpleasant, putrid smell,
unusual discolouration that does not go away,
a persistent and obvious deterioration of the grains, for example if they fall apart or become slimy,
a sudden, complete change in grains that previously worked well.

If you see mould, throw away both the kefir and the grains. In that case, it is not worth experimenting with saving the culture.

If your newly purchased kefir grains still do not ferment the milk properly after two or three weeks of regular, stable care, or if you are unsure about their condition, get in touch with us and we will help you find out what the problem might be.

🔬 Good to know

The best measure of your kefir grains' health is not their size but the kefir they make. If the milk regularly thickens and turns pleasantly tangy, and the grains are intact and elastic, the culture is working well, even if it grows more slowly than you expected. You can improve the rate of growth by fine-tuning the conditions, but it takes patience: kefir grains are a living community that adapts at its own pace.

In short

The most common reasons for slow kefir grain growth are an unsuitable temperature, a change in milk or poor milk quality, too many grains in too little milk, overly long fermentation and infrequent milk changes, unnecessary washing, and the time the culture needs to adapt. Weigh your grains weekly, provide stable conditions and change only one thing at a time. If your kefir grains make good kefir, they are healthy, and with proper care they will multiply over time.

Why Aren't My Kefir Grains Multiplying?