Fermentationist
Make / Kefir

Method · Updated on 9 October 2026

How to make kefir with grains

Kefir grains, milk and a day at room temperature: how much grain to use, how long to ferment, how to strain and how to look after the grains.

You need
Kefir grains, pasteurised milk
Ferment
18–24 hours at 18–29 °C 1
Grains
About 2 tablespoons per 2 cups milk 1
Work out the grainsStart a Batch CardSomething went wrong?
A glass of kefir beside a small bowl of kefir grains

Kefir grains are small, gelatinous clusters of lactic acid bacteria, acetic acid bacteria and yeasts living together. 4 Put in milk at room temperature, they sour and slightly thicken it in about a day; the grains are then strained out and used again.

You need

  • 500 ml pasteurised milk; not ultra-pasteurised or UHT 1
  • About 2 tablespoons of kefir grains per 2 cups (about 500 ml) of milk. Research uses 20–50 g of grains per litre, and there is no fixed household rule 12

Equipment

  • A clean glass jar
  • A cloth or coffee filter and a rubber band to cover it 1
  • A plastic, fine nylon or stainless steel strainer 1

Method

  1. Combine

    Put the grains in the jar and pour in the milk. 1

  2. Cover

    Cover with a cloth or coffee filter held by a rubber band, and keep the jar out of direct light. 1

  3. Ferment

    Leave at 18–29 °C (65–85 °F) for 18–24 hours. Traditional practice is 20–25 °C for about 24 hours. 12

  4. Check

    It is ready when slightly thickened with an acidic aroma. 1

  5. Strain

    Strain out the grains and refrigerate the kefir. 1

  6. Start again

    Put the grains straight into fresh milk for the next batch. The grains grow; remove the surplus so the ratio stays about the same. 3

How to tell it is ready

  • Slightly thickened, with an acidic aroma 1
  • pH 4.0–4.5, if you test 1
  • A little separation is normal when it has gone a bit long 1

Storing it

  • Refrigerate finished kefir straight after straining. We have not found a primary source for how long homemade kefir keeps; drink it within a few days and discard it if it smells off or shows mould
  • For a long break, grains can be frozen: storage at −20 °C is a good method to preserve grains for home use 5

Milder or tangier

More milk to the same grains, or a shorter time, gives a milder kefir; more grains, a longer time or a warmer room gives a tangier one. 13 Temperature also controls how much acid, alcohol and carbon dioxide the culture makes. 3 Change one of these at a time and note the result.

Next batch: change one thing

Write down what you did in a Batch Card, change a single variable (time, temperature, starter or ingredient) and compare. Problems? See Kefir problems and fixes.

Sources

  1. Colorado State University Extension: Understanding and making kefir2 tablespoons of grains per 2 cups of pasteurised, not ultra-pasteurised or UHT, milk; 18–29 °C (65–85 °F) in the dark for 18–24 hours; ready when slightly thickened with an acidic aroma, pH 4.0–4.5; strain with plastic, nylon or stainless steel; a shorter time or more milk fixes a watery whey layer. Accessed 2026-10-09.
  2. Garrote et al. (1998), Characteristics of kefir prepared with different grain:milk ratios, Journal of Dairy ResearchTraditional kefir is fermented at 20–25 °C for about 24 hours; studies use 20–50 g of grains per litre; there are no rules for household kefir. Accessed 2026-10-09.
  3. Tetra Pak Dairy Processing Handbook: Fermented milk productsIndustrial yogurt milk is heated to 90–95 °C for about 5 minutes; incubation 4–5 hours at 42–43 °C to pH 4.2–4.5; concentrated yogurts including strained yogurt and skyr lose whey after fermentation; raising protein too high before fermentation risks sandiness; kefir is made with 1:20–1:30 grains to milk at about 23 °C for about 20 hours; temperature controls the acid, alcohol and carbon dioxide in kefir. Accessed 2026-10-09.
  4. Codex Alimentarius: Standard for fermented milks (CXS 243-2003)Defines yogurt and kefir by their cultures; kefir grains hold lactic acid bacteria, Acetobacter and yeasts; concentrated fermented milks such as strained yogurt have protein raised to at least 5.6%. Accessed 2026-10-09.
  5. Garrote et al. (1997), Preservation of kefir grains, a comparative study, LWTStorage at −20 °C is a good method to preserve kefir grains for household manufacture. Accessed 2026-10-09.
  6. US FDA: The dangers of raw milkRaw milk can carry Salmonella, E. coli, Listeria and Campylobacter; soft cheeses and yogurt made from it are high-risk. Accessed 2026-10-09.
  7. UConn Extension: Handling food with mould (citing USDA FSIS)Yogurt, sour cream and soft cheeses such as cottage and cream cheese are discarded entirely if any part is mouldy. Accessed 2026-10-09.
  8. University of Alaska Fairbanks Cooperative Extension: Making yogurt at home (FNH-00062)Heat to 85–93 °C (185–200 °F) for 10–20 minutes, do not boil; culture is killed above 54 °C (130 °F) and grows poorly below 37 °C (98 °F); adding culture to milk over 46 °C (115 °F) can kill it; incubate 4–7 hours at 43 °C (110 °F); sets at pH 4.6; one 5 g freeze-dried packet or ¼ cup yogurt per quart; discard batches that fail to set or show microbial growth or odd odours; keeps about 10–21 days at 4 °C. Accessed 2026-10-09.

Numbers on this page come from these sources. Where sources give a range, we quote the range rather than a single figure.

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