How do I look after milk kefir grains?

Milk kefir grains are a rubbery, cauliflower-looking symbiotic colony of bacteria and yeasts. They are not a starter you use up — they grow, and with a daily feed of fresh milk they carry on indefinitely. Almost every kefir problem is a ratio or temperature problem, and both are easy to adjust once you can read the signs.

Safety

What you'll need

• Milk kefir grains
• Pasteurised whole milk
• A glass jar with a loose lid or a cloth
• A plastic or nylon sieve and a plastic or wooden spoon

Step by step

1. Use a ratio of roughly one part grains to ten parts milk.A tablespoon of grains to about 250ml of milk is a typical starting point. Too many grains for the milk gives a sour, over-fermented, separated result in a few hours; too few takes days.
2. Use pasteurised whole milk to begin with.Cow, goat or sheep milk all work. Whole milk gives the best texture. UHT works but the grains do less well on it long term. Plant milks do not sustain the grains — they need lactose — so a coconut or oat kefir means keeping a separate set of grains in dairy milk to rest in.
3. Cover loosely, never sealed.A cloth and a band, or a lid resting on. Kefir produces carbon dioxide and a sealed jar builds pressure. Keep it out of direct sunlight.
4. Leave it 12 to 24 hours at room temperature.18 to 24°C. It is ready when it has thickened to the texture of thin yoghurt, smells pleasantly sour and yeasty, and clings to the side of the jar when tilted. In a warm kitchen this can be eight hours; in a cold one it can be thirty.
5. Strain with plastic or nylon, not metal.Pour through a sieve into a bowl, stirring gently with a plastic or wooden spoon to push the kefir through. Brief contact with stainless steel is fine, but prolonged contact with reactive metals is not good for the grains.
6. Put the grains straight into fresh milk.Do not rinse them. The film of kefir on them is part of the culture, and rinsing — especially in chlorinated tap water — sets them back. Straight from the sieve into the next jar.
7. Refrigerate the finished kefir.It keeps a week or more in the fridge and gets tangier. If you want it fizzier and more complex, leave the strained kefir at room temperature in a covered bottle for a further twelve hours before refrigerating — a second ferment — but burp the bottle, because it builds pressure.
8. Pause it when you go away.Put the grains in a jar of fresh milk in the fridge. They will sit happily for two to three weeks, fermenting very slowly. Change the milk when you get back and expect two or three sluggish batches before they are back to normal.
9. Give away or dry the surplus.The grains multiply. Pass them on, or rinse and dry a spoonful on kitchen paper for a few days and keep them in a jar of milk powder in the freezer as a backup.

Tips

• If kefir is too sour, use less grain or more milk, or ferment for less time. If it is thin and milky, give it longer or use more grains.
• New grains often take a week or two of daily feeding to hit their stride. Do not judge them on the first three batches.
• Kefir separating into curds and clear whey means it has fermented too far — shake it back together, and shorten the time or increase the milk next round. It is still perfectly good to drink.
• Grains that stop growing usually want a warmer spot, whole rather than skimmed milk, or a bigger volume of milk.

Common mistakes

• Rinsing the grains between batches — It strips the culture film off them and, in chlorinated water, kills part of the colony. Grains go straight from the sieve into fresh milk.
• Sealing the jar tightly during fermentation — Carbon dioxide builds up with nowhere to go. At best it fizzes over when opened; a sealed glass bottle left through a long second ferment is a genuine hazard.

If it doesn't work

Questions people ask