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How to make milk kefir at home with kefir grains

Kefir grains in a jar of pasteurized milk, left on the counter for a day. It is the easiest ferment to keep going, and kefir has one of the better-supported uses in the kitchen: easier lactose digestion.

By the editors of Alimentotherapy Last reviewed 5 min read Not medical advice

Makes
About 2 cups
Hands-on
5 minutes
Total time
18 to 24 hours

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The short answer

Stir 2 tablespoons of live milk kefir grains into 2 cups of pasteurized (not ultra-pasteurized) milk, cover with cloth and leave at 65 to 85°F for 18 to 24 hours, then strain out the grains and refrigerate the kefir for up to 2 weeks, per Colorado State University Extension Colostate. The best evidence is for lactose digestion: in a trial of 15 adults with lactose maldigestion, kefir cut breath hydrogen, a marker of undigested lactose, compared with milk Hertzler 2003, and our yogurt and kefir page grades that use strong.

Ingredients and method

Ingredients

  • 2 tablespoons active (live) milk kefir grains
  • 2 cups pasteurized cow's or goat's milk, not ultra-pasteurized or UHT

Equipment

  • Two 1-quart glass canning jars, one with a lid
  • Cheesecloth (2 layers) or 2 to 3 coffee filters, and a rubber band or jar ring
  • Plastic or wooden spoon
  • Plastic, fine nylon mesh or stainless steel strainer
  • Dish soap (not antimicrobial); optional white vinegar or a fermentation sanitizer
  • Optional: pH test strips

  1. Clean

    Wash your hands and all equipment with plain dish soap (not antimicrobial soap) and rinse well. Optionally sanitize with white vinegar or a fermentation sanitizer.

  2. Combine

    Put the grains in a clean jar, pour in the milk and stir gently with a plastic or wooden spoon.

  3. Cover

    Cover the jar with 2 layers of cheesecloth or 2 to 3 coffee filters and secure with a rubber band or jar ring, so air can move but dust and insects stay out.

  4. Ferment 18 to 24 hours

    Set the jar somewhere dark at 65 to 85°F. After 18 to 24 hours the kefir should be slightly thickened with a clean, sour smell. A yellowish watery layer is separated whey: stir it back in or pour it off, and use a shorter time or more milk next batch.

  5. Check the acidity (optional)

    A pH strip should read about 4.0 to 4.5. Dairy ferments need to reach pH 4.6 or lower within 48 hours; if yours has not soured by then, discard it.

  6. Strain and store

    Strain the kefir through the strainer into the second jar, lid it and drink it straight away or refrigerate for up to 2 weeks.

  7. Start the next batch

    Rinse out the fermenting jar, put the grains back in and add fresh milk. The grains multiply over time; share or compost the extra.

If you need the equipment

What kefir grains are

Kefir grains are not grains. They are small, rubbery clusters that look like cauliflower florets, made of lactose-fermenting yeasts and lactic and acetic acid bacteria held in a protein and sugar matrix called kefiran. Yogurt is fermented by bacteria alone; kefir is fermented by bacteria and yeasts togetherColostate. That is why it tastes sharper and can be faintly fizzy.

Milk grains and water kefir grains are different cultures and cannot be swapped Colostate. If you want a dairy-free ferment, see water kefir.

In the kitchen

Why not ultra-pasteurized milk? Colorado State notes it is heated to 275°F or higher, enough to change some milk proteins; ordinary pasteurization heats milk to 161°F for 15 to 20 seconds Colostate.

The safety endpoints: pasteurized milk and pH

Start with safe milk. The FDA says raw milk can contain a variety of disease-causing pathogens, and that pasteurization kills them without any significant impact on milk’s nutritional quality FDA. Fermentation adds acidity, but it is not a substitute for pasteurization.

Then make sure the batch sours. Utah State University Extension says fermented foods must reach pH 4.6 or less in the allotted time to be considered safe, and dairy products must get there within 48 hours Usu. A healthy kefir batch usually reaches pH 4.0 to 4.5 in 18 to 24 hours Colostate, so a jar that is still sweet and thin after two days has a problem with the grains or the temperature and should go down the drain.

What the evidence says about kefir

Lactose digestion. In a randomized study, 15 adults with lactose maldigestion drank milk, kefir or yogurt, each carrying 20 g of lactose. Breath hydrogen (it rises when lactose goes undigested) was much lower after plain kefir than after milk, and kefir and yogurt cut perceived flatulence by 54 to 71 percent relative to milkHertzler 2003. Together with the wider evidence on live yogurt cultures, that gives our yogurt and kefir page its strong grade for digesting lactose.

Gut microbes. Beyond lactose, the evidence is the general fermented-food picture: a small Stanford trial found a high-fermented-food diet raised gut microbiota diversity and lowered inflammatory markers Wastyk 2021. It is graded limited on the fermented foods page. Colorado State adds that every homemade batch varies in its microbes, making specific health effects hard to pin down Colostate.

Comparing options? See kefir vs yogurt and kombucha vs kefir.

Getting grains

Grains are passed between friends, and they grow, so anyone who makes kefir usually has spares. Live grains need to go into milk or the refrigerator quickly; dehydrated grains have a longer shelf lifeColostate.

Food safety

  • Use pasteurized milk. Raw milk can carry disease-causing bacteria, and fermenting it does not make it safe.
  • Discard any batch that has not soured to pH 4.6 or below within 48 hours, or that smells rotten or grows fuzzy mold.
  • Refrigerate finished kefir and use within 2 weeks.
  • Start with a small glass (4 to 6 ounces a day): kefir can cause cramps, gas or nausea at first.
  • Fermenting does not remove milk proteins: kefir is not safe for anyone with a milk allergy.
  • If you are seriously ill or immunocompromised, ask your care team before adding live-culture foods.
  • If you take tetracycline or quinolone antibiotics, ask your pharmacist about spacing them from dairy.

Common questions

How long should milk kefir ferment?

18 to 24 hours somewhere dark at 65 to 85 degrees F, using 2 tablespoons of grains per 2 cups of milk, according to Colorado State University Extension. It is ready when slightly thickened and sour-smelling; a pH strip should read about 4.0 to 4.5.

Can I make kefir with raw milk?

It is safer not to. The FDA says raw milk can contain a variety of disease-causing pathogens and that pasteurization kills them without significantly affecting nutrition. Colorado State Extension's method uses pasteurized, not ultra-pasteurized, milk.

Is kefir good for lactose intolerance?

Often, yes. In a trial of 15 adults with lactose maldigestion, plain kefir produced far less breath hydrogen than milk with the same lactose, and kefir and yogurt cut flatulence by 54 to 71 percent compared with milk.

Sources

Primary research and government sources, each checked on the date this page was reviewed.

  1. GuidelineColorado State University Extension (Food Smart Colorado). Understanding and Making Kefir.
  2. GuidelineUtah State University Extension. Tips to Safely Ferment at Home.
  3. FDAU.S. Food and Drug Administration. Raw Milk Misconceptions and the Danger of Raw Milk Consumption.
  4. PubMedHertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc. 2003. PMID 12728216.
  5. PubMedWastyk HC, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021. PMID 34256014.

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