Most kefir problems come from three things: too much heat, too many grains for the milk, or too long between feedings. Find your symptom below, change one thing at a time, and give the next batch a full day before you judge it.
Quick fixes
| What you see | Most likely reason | What to change |
|---|---|---|
| Kefir is thin and has not thickened | Too short a time, a cool room, or low-fat milk | Give it up to 24 hours at 20 to 29°C and use full-cream milk. See “My kefir will not thicken” below. |
| Kefir is very sour, or ready in under 12 hours | A warm room, or too many grains for the milk | Use fewer grains or more milk, move the jar to the coolest room and start checking at 6 to 8 hours. |
| Kefir has split into curds and whey | It cultured for too long | Whisk or strain it. It is fine to drink if it smells pleasantly sour. Next time use less grain, more milk, a cooler spot or less time. |
| It smells yeasty, or a little fizzy | Warm weather and plenty of yeast activity | Normal if it smells pleasantly sour and looks clean. If it smells rotten, throw it away. |
| The grains are not multiplying | They are slow, and some sets never grow much | Wait. Grains often take 6 to 8 weeks to start multiplying. They still make kefir. |
| The grains float to the top | Gas collects in the thickening milk | Common, and not a problem by itself. Judge the kefir by its smell, taste and look. |
| The grains are stuck in a layer of cream | Loose or non-homogenised milk lets the cream rise | Stir or swirl the jar 3 or 4 times a day, and mix the cream back in before you strain. |
| Fuzzy spots, or pink, orange, red, green or black patches | Mould or contamination | Throw everything away, grains included. Wash the jar well and start again with fresh grains. |
My grains are not growing
New grains can take 3 to 7 days to start working, and dehydrated grains need about a week of daily batches to wake up. After that, growth is slow. Grains generally take 6 to 8 weeks after they are revived to start multiplying, and some sets never multiply much. Either way they can be used for years, and a set that does not grow still makes good kefir.
My kefir will not thicken
Kefir should not be ready in under 12 hours, and many people find 14 to 24 hours about right. A cool room, low-fat milk, or too little grain for the amount of milk can all slow a batch. Try these in order:
- Move the jar somewhere warmer, within 20 to 29°C and out of direct sun.
- Use full-cream milk. Low-fat milk gives a thinner kefir.
- Use a little more grain, or a little less milk.
If a batch that used to thicken suddenly will not, something has changed: the milk, the season or the room. Replace about an eighth of the fresh milk with finished kefir, and repeat for one to three batches.
My kefir is too sour, or has separated
Sour kefir and split kefir are the same problem seen early and late: the culture has had more time or warmth than it needed. Use fewer grains (toward 1 teaspoon for a litre of milk rather than 2), use more milk, move the jar to the coolest room and check earlier. Kefir should form within 48 hours at the very latest. If it has already split into curds and whey, whisk it or strain it and drink it, or blend it into a smoothie, as long as it smells pleasantly sour.
Why do my grains float?
Grains often rise to the top of the jar as a batch thickens, because gas gets trapped in the milk around them. It is common, especially in warm weather, and it is not a sign that anything is wrong. Look at the kefir rather than the grains: it should smell pleasantly sour, with no fuzzy spots and no odd colours.
What should kefir smell like?
Pleasantly sour, and sometimes a little yeasty. A fresh yeast smell is normal, especially in hot weather. A rotten smell is not normal: throw that batch away.
Is it mould? A short checklist
- Fuzzy, dry or raised spots in white, green, orange, red or black, or pink milk, mean mould.
- Grains that turn pink, orange, red, green or black may be contaminated.
- Yellow or light caramel grains are normal.
- A white film on top can be yeast or mould. If you cannot tell, send us a photo on WhatsApp before you decide.
If it is mould, throw away the whole batch, grains included. Do not try to rescue them. Mould is uncommon in kefir that is fed every day in a clean jar.
I left the grains for days
Grains left in the same milk for more than 48 hours may starve. If it happened once, move them into fresh milk straight away: they are probably fine. The separated kefir is fine to drink if it smells and tastes right.
My grains got too hot
Heat stops kefir grains working. If they went into milk that was still hot, or sat somewhere very hot, they will not culture again and should be replaced. This is why our guide says to cool boiled milk below 30°C before the grains go in.
A simple routine that avoids most problems
- Use 1 to 2 teaspoons of grains for up to 1 litre of full-cream milk.
- Keep the jar at 20 to 29°C, out of direct sun.
- Strain every 12 to 24 hours, at about the same time each day.
- Use a clean jar, a clean cloth cover and a plastic or nylon strainer.
- Put the grains straight into fresh milk, or into the fridge if you need a break.
The whole method is in How to make milk kefir at home. If you need a fresh start or a backup, see Live Milk Kefir Grains and Dehydrated Milk Kefir Grains.
Still stuck? Send us a photo on WhatsApp and we will tell you what is happening.
Sources: Cultures for Health, Milk kefir troubleshooting, and Milk kefir: temperature and culturing time, opened 10 October 2026. Written by KefirBuy.
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