Milk kefir: grains, care and rest
Milk, grains and a day. What makes a good kefir, how to keep the grains healthy from one batch to the next, and what to do with them when you stop.
8 min read First steps Reviewed October 26, 2026 52 facts, each with its source
What the grains are
Kefir grains are yeasts and lactic and acetic acid bacteria living together in a matrix of protein and sugars called kefiran1. They measure 0.3 to 4 cm (⅛ to 1½ inches), look like little cauliflower florets and range from white to yellow2. In yogurt only bacteria ferment; in kefir, yeasts do too3. And the milk doesn't need warming4. Kefir began centuries ago near the Caucasus Mountains5, and its grains aren't grains of any cereal: they're named for how they look6.
The grains ferment milk in a day, then they're strained out and used again. Milk grains don't work for water kefir, or the other way around7.
Getting and activating the grains
Kefir grains are shared between friends or bought online or in health food stores8. They come live or dehydrated: live grains have to be used or put in the fridge right away, and dehydrated ones keep longer9. There's also powdered kefir culture, but it has fewer microbes than grains10.
Dehydrated grains are activated in pasteurized milk: a 2 to 5 g pack per 250 ml (1 cup), or whatever the maker says11. When the milk thickens, the grains are strained out and that milk is thrown away12. This is repeated, with a little more milk each time, until they can ferment a full batch of a liter (1 quart) or more13. They're active when they float or when the milk clots14. Frozen or freeze-dried grains can take up to a month15.
The milk
Use pasteurized milk, but not UHT or ultra-pasteurized: it's heated so much that some of its proteins change16. The guides always call for pasteurized milk17. Raw milk can carry pathogens18, and kefir's acidity isn't enough to stop them all: below pH 4.5 it holds back many, but E. coli, Listeria and Salmonella can survive19.
Whole or reduced-fat milk both work. With more fat, the grains grow less20.
Fermenting: 18 to 24 hours
Wash your hands and the equipment with ordinary soap, not antibacterial21. Put the grains in a glass jar: 2 to 10% of the weight of the milk22. Fervida uses 5%, 25 g per 500 ml (2 cups), and that's a house rule: more grains make it more sour23. Add the milk and stir with a plastic or wooden spoon24. Cover with two layers of cheesecloth or two or three coffee filters and a rubber band25.
Leave it in a dark place, at 18–29 °C (65–85 °F), for 18 to 24 hours2627. It's ready when it has thickened slightly and smells sour28. With strips, the pH should be between 4.0 and 4.529. BCCDC, British Columbia's public health agency, counts the batch as failed if it hasn't dropped to 4.6 within 36 hours30.
If you see a yellow, watery layer, that's whey: strain it off or stir it back in31. Next time, give it less time or more milk32. Don't stretch it much past a day: after 48 hours, it can go above 1.1% alcohol33.
Straining and storing kefir
Strain it through a plastic, nylon mesh or stainless steel strainer34 into another jar with a lid35. The grains stay in the strainer. Whatever you don't drink goes in the fridge within 4 hours36, at 5 °C (41 °F) or below.
CSU, Colorado State University Extension, gives it up to 2 weeks in the fridge37, and that's what Fervida uses. BCCDC recommends 3 to 12 days38. If you'd rather keep the shorter margin, drink it within 12 days.
Caring for the grains
After straining, rinse and wash the jar, put the grains back and add fresh milk39. Don't rinse the grains with water: they grow less40.
The grains grow: in one study they gained 60% in weight in 8 days41. Batch after batch is what keeps their balance of yeasts and bacteria42. Weigh them now and then and keep 25 g per 500 ml. You can give away the extra.
Look at them every batch: their color, their shape, their smell and how well they ferment43. If one day you can't strain it on time, put the jar in the fridge with the grains still in: the cold slows it down, and you strain it the next day.
When you stop: resting the grains
- A short break. In the fridge, in fresh milk, they keep for up to 7 days; in water, up to 344. Milk is better, because water slows their growth.
- After the break. They lose activity and need reactivating45: one or two batches with a little milk, thrown away, until they thicken milk in a day again.
- A long break. Air-dried or freeze-dried, in the fridge or the freezer, they keep their activity for 12 to 18 months46. In one study, freezing them in milk at −20 °C (−4 °F) kept them best47. Once you take them out, activation can take up to a month.
If you're away for a week, move them to a clean jar, cover them well with fresh milk, close it and keep it in the fridge. When you're back, throw that milk away and start with a small batch.
What can go wrong
| What you see | What it is | What to do |
|---|---|---|
| Fuzz or colored spots | Mold, which can reach below the surface48 | Throw it all out, grains included, and don't sniff it49 |
| Grains that grow slowly, change color or smell, or stop fermenting | Grains that aren't working50 | Throw them out |
| It doesn't thicken or reach pH 4.6 in 36 hours | A failed batch | Throw it out and check the grains |
| A yellow, watery layer | Whey | Strain it or stir it in; next time, less time |
| Very sour | Too many grains or too much time | Take out some grains or strain sooner |
Who it's for
The recipes
- Milk kefir: the base recipe, with 25 g of grains per 500 ml of milk.
- Fruit-flavored milk kefir: the fruit goes into kefir that's already strained, without the grains.
- Kefir cheese: kefir strained through cloth, always in the fridge, until it's spreadable.
Where every number comes from
Every number in the text leads to its figure: the exact sentence from the official guide it comes from, in its own language.
-
1
Yeasts and lactic and acetic acid bacteria, in a matrix called kefiran
“Kefir grains consist of lactose-fermenting and non-lactose fermenting yeasts as well as lactic- and acetic acid- producing bacteria, surrounded by a protein matrix called kefiran.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
2
0.3 to 4 cm, like cauliflower florets, white to yellow
“Milk kefir grains range in size from 0.3 to 4 cm in length and look similar to small clumps of cauliflower florets, white to yellow in colouration.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
3
In kefir, yeasts and bacteria ferment; in yogurt, only bacteria
“However, both yeast and bacteria contribute to kefir’s fermentation, whereas only bacteria are involved in the making of yogurt.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
4
The milk doesn't need warming
“no warming is required”
UF/IFAS Extension (University of Florida) · Fermented Foods: Kefir (FSHN24-2/FS457, 2024) · read on October 20, 2026
-
5
It began centuries ago near the Caucasus
“Milk kefir (pronounced kuh-feer) is a fermented beverage that originated centuries ago near the Caucasus Mountains in Eastern Europe.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
6
They aren't grains: they're named for how they look
“Despite the name, kefir grains are not actually grains; rather, they are named for their similar appearance”
UF/IFAS Extension (University of Florida) · Fermented Foods: Kefir (FSHN24-2/FS457, 2024) · read on October 20, 2026
-
7
Milk grains don't work for water kefir
“milk grains cannot be used to make water kefir or vice versa.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
8
Shared between friends or bought online or in stores
“Kefir grains may be shared between friends or purchased from online retailers or some health food stores.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
9
Live grains have to be used or chilled right away; dehydrated ones keep longer
“Live grains will need to be fermented or refrigerated very quickly, whereas the dehydrated variety will have a longer shelf-life.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
10
Powdered culture has fewer microbes than grains
“Kefir culture is usually in the form of a dry powder that will contain fewer microorganisms than kefir grains.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
11
A 2 to 5 g pack of dehydrated grains per 250 ml of milk
“one pack containing between 2 to 5g of dehydrated kefir grain to 250mL of milk or more”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
12
Once it thickens, the grains are strained out and the milk is thrown away
“When the texture becomes gel like, separate the grains from the milk by a strainer and discard the liquid.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
13
Repeated until they ferment a full batch, a liter or more
“The process is repeated until the grains can ferment a full batch, generally one litre or more.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
14
They're active when they float or when the milk clots
“When the kefir grains float to the surface of milk or when the milk clots, the activation process is completed.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
15
Frozen or freeze-dried, they can take up to a month
“If the grains are frozen or freeze-dried, the activation process can take longer (up to 1 month)”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
16
Pasteurized, but not UHT or ultra-pasteurized
“Select milk which has been pasteurized (heated to 161° F for 15-20 seconds) but not ultra-pasteurized (UP) or labeled UHT (ultra-high temperature treatment) because these products are heated to 275° or higher, denaturing certain proteins.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
17
Pasteurized milk, and the fridge at 41 °F or below
“kefir should be made with pasteurized milk and quality kefir grains and refrigerated after fermentation (≤ 41°F).”
UF/IFAS Extension (University of Florida) · Fermented Foods: Kefir (FSHN24-2/FS457, 2024) · read on October 20, 2026
-
18
Raw milk can carry pathogens
“Raw drinking milk (RDM) has a diverse microbial flora which can include pathogens transmissible to humans.”
EFSA · Scientific opinion on the public health risks related to the consumption of raw drinking milk (2015) · read on October 20, 2026
-
19
At pH below 4.5, some pathogens survive
“Fermented kefir with a pH < 4.5 suppresses many pathogens, but E. coli, Listeria, and Salmonella can survive”
UF/IFAS Extension (University of Florida) · Fermented Foods: Kefir (FSHN24-2/FS457, 2024) · read on October 20, 2026
-
20
With more fat in the milk, the grains grow less
“higher milk fat content impairs grain growth by inhibition of nutrient exchange”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
21
Hands and equipment washed with ordinary soap
“Wash hands and clean all equipment with soap (not anti-microbial)”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
22
2 to 10% grains to milk
“Grain to milk ratio, usually varying between 2% and 10% (w/v)”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
23
More grains, more acid
“higher rates of grain inoculum increase lactic acid levels, providing sharper pH lowering”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
24
A plastic or wooden spoon
“Plastic or wooden spoon”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
25
Two layers of cheesecloth or 2 or 3 coffee filters
“Cover with 2 layers of cheesecloth or 2 or 3 coffee filters and secure with rubber band or jar ring.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
26
In a dark place, at 65–85 °F
“Set in a dark place at a temperature between 65° and 85° F (18°-29° C).”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
27
18 to 24 hours
“Allow to ferment for 18-24 hours.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
28
Slightly thickened, with a sour smell
“Kefir should be slightly thickened and have an acidic aroma.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
29
pH between 4.0 and 4.5
“Optional: Check pH using test strips (should be in the 4.0-4.5 range)”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
30
If it doesn't drop to 4.6 within 36 hours, the batch has failed
“If pH does not drop to 4.6 or less within 36 hours, the batch has failed.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
31
The yellow layer is whey
“If there is a yellow, watery layer, this is due to separation of the whey which has separated and can be strained off or remixed into the kefir.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
32
Less time or more milk
“A shorter fermentation time or more milk may fix this problem.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
33
Past 48 hours, it can go above 1.1% alcohol
“Fermentation times greater than 48 hrs may lead to alcohol contents of >1.1% ABV.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
34
A plastic, nylon mesh or stainless steel strainer
“Plastic, fine nylon mesh, or stainless steel strainer”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
35
Strained into another jar with a lid
“Strain the milk from the grains into another standard canning jar (with lid) or any air-tight storage bottle.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
36
Once strained, into the fridge within 4 hours
“Following filtration, the milk kefir should be cooled down within 4 hours and refrigerated at 4oC.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
37
In the fridge, up to 2 weeks
“Drink immediately or refrigerate for up to 2 weeks.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
38
BCCDC recommends 3 to 12 days
“The recommended shelf life for traditional style milk kefir made with kefir grains under hygienic, good manufacturing practices is between 3-12 days.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
39
A clean jar, the same grains and fresh milk
“Rinse out and clean the fermentation jar, put the grains back into it, and add milk.”
Colorado State University Extension (FoodSmart Colorado) · Understanding and Making Kefir · read on October 20, 2026
-
40
Rinsed with water, they grow less
“growth of the grains is retarded when they are rinsed with water after each sieving”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
41
60% more grains in 8 days
“after 8 days of successive fermentations the biomass grains had an increment of 60% when compared to the initial weight of the grains”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
42
Batch after batch keeps the balance of yeasts and bacteria
“The viability of kefir grains is guaranteed through maintenance of the bacterial/yeast ratio achieved by continuous fermentation cycles that lead to their biomass increase”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
43
Watch their color, shape, smell and activity
“by monitoring grains for healthy colour, shape, odour and activity”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
44
In milk, up to 7 days; in water, up to 3; always in the fridge
“When re-using milk kefir grains, store in fresh milk for up to 7 days, or in water for up to 3 days at refrigeration temperatures for optimal activity.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
45
After that they lose activity and need reactivating
“After this period, kefir grains will lose their activity, and will require activating again.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
46
Dried or freeze-dried, 12 to 18 months in the fridge or freezer
“For longer term storage, milk kefir grains that are air-dried or freeze-dried and kept refrigerated or frozen can retain microbial activity for 12-18 months.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
47
Frozen in milk at −4 °F, they kept best
“Kefir grains were maintained in milk and preserved by storage in a freezer at −20 ± 2 °C, which proved to be the best method for grain preservation and can also be used to maintain the grains for household kefir production”
Foods (MDPI), Alves et al., via PubMed Central · Characterization of Kefir Produced in Household Conditions: Physicochemical and Nutritional Profile, and Storage Stability (2021) · read on October 20, 2026
-
48
Like moldy yogurt, the whole thing goes
“Yogurt and sour cream Discard Foods with high moisture content can be contaminated below the surface.”
USDA Food Safety and Inspection Service · Molds on Food: Are They Dangerous? · read on October 20, 2026
-
49
Don't sniff mold
“Don't sniff the moldy item. This can cause respiratory trouble.”
USDA Food Safety and Inspection Service · Molds on Food: Are They Dangerous? · read on October 20, 2026
-
50
If they grow slowly or change color or smell, they go
“If kefir grains grow slowly, if the grains develop unusual colour, odour, or if grains lose activity, grain function is compromised, and they should be discarded.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
-
51
People at risk may want to skip homemade kefir
“those with compromised immune systems (i.e., infants, pregnant women, elderly, or those who are chronically ill or have autoimmune disorders) may want to avoid homemade kefir”
UF/IFAS Extension (University of Florida) · Fermented Foods: Kefir (FSHN24-2/FS457, 2024) · read on October 20, 2026
-
52
It may contain alcohol: not for children or pregnant women
“kefir may contain alcohol produced during the fermentation process (Rahmatullah et al., 2023) and, if so, it would not be appropriate for children and pregnant women.”
UF/IFAS Extension (University of Florida) · Fermented Foods: Kefir (FSHN24-2/FS457, 2024) · read on October 20, 2026