Fermenting kefir with soy milk and other plant milks

By Nik, founder of 東歐嚴選｜kefir.link and former chef · First published 26 October 2024 · Updated 3 November 2026

Soy milk is on the breakfast table in many homes. Your milk kefir grains can ferment it too. In about 18 hours, plain soy milk turns into a tangy, pale-yellow drink with a clear soy flavour. You need the right soy milk, a little less grain than for cow’s milk, and one batch of cow’s milk now and then to keep the grains lively.

The short answer

• Yes, it works: milk kefir grains ferment soy milk in about 18 hours.
• Start after the first week: feed new grains whole cow’s milk for a week, then switch to soy milk.
• Use fewer grains: 1 part grains to 50 parts soy milk in summer, and 1 to 30 in winter.
• Unsweetened soy milk works: if it ferments slowly, add 1 teaspoon of sugar per 500 ml.
• Ready when it is thick and pleasantly sour: finish it within 36 hours.
• Keep the grains lively: after about 6 batches in soy milk, give them one batch in fresh cow’s milk.

Get live kefir grainsTry our soy milk kefir

How we checked this guide

• Our own care guide: the ratios, times and the cow’s milk batch come from the printed guide we send with our grains, and from the questions customers ask us on LINE.
• Kefir grains in soy milk: a 2025 study that kept kefir grains in soy milk for four months (study).
• Taste: a National Taiwan University study of the aroma of soy milk kefir (study).
• Food safety: the kefir guidance of the BC Centre for Disease Control (BCCDC).
• Coconut milk: the University of Guam extension guide to coconut kefir (PDF).
• Soy milk labels and homemade soy milk: Taiwanese food-label rules as reported by foodNEXT (foodNEXT), and a dietitian’s advice on boiling soy milk (TVBS).

How soy milk feeds the grains

• Cow’s milk sugar is lactose. Kefir grains grow best on it.
• Soy milk has its own sugars: about half is ordinary sugar, and the rest are bean sugars (study).
• The grains ferment these sugars quickly, so soy milk is ready sooner than cow’s milk, in about 18 hours.
• The grains grow slowly in soy milk. This is normal. One batch of cow’s milk every so often keeps them growing.

Which soy milk to use

• Plain packaged soy milk, freshly opened: it is clean and ready to use. Pour it straight from the carton.
• Unsweetened works well: a carton labelled 無糖 (unsweetened) has less than 0.5 g of sugar per 100 ml (foodNEXT).
• If it ferments slowly, stir 1 teaspoon of sugar into each 500 ml of soy milk before you add the grains.
• Homemade soy milk: boil it thoroughly, then let it cool to room temperature before you add the grains (TVBS).
• Choose plain soy milk rather than flavoured soy drinks, so the grains get a simple, clean base.

For cow’s milk, read Milk Matters: which milk makes good kefir.

How much soy milk for your grains

Soy milk ferments faster than cow’s milk, so the same grains need more soy milk. These are the ratios from our care guide:

Soy milk changes a little from day to day with the weather. Start with the table, then adjust by a little each batch until it suits your kitchen.

For more on summer and winter, read Why temperature matters when making kefir.

How to make soy milk kefir, step by step

1. Settle the grains first. Feed new grains whole cow’s milk for the first week, as in How to make kefir. Switch to soy milk once they ferment milk well.
2. Clean and dry everything. Wash the jar, strainer and spoon, rinse them well and let them dry completely.
3. Weigh the grains and pour the soy milk. Use the ratio for the season from the table.
4. Cover and wait. Cover the jar with kitchen paper and a rubber band. Leave it on the counter at room temperature, below 35°C, for about 18 hours. The grains do all the work, so you need no rice cooker or yogurt maker.
5. Check it. Tilt the jar gently. Ready soy milk kefir has thickened and tastes pleasantly sour. Taste it with a clean spoon.
6. Still thin? Close the jar and wait a few more hours. Finish within 36 hours in total.
7. Strain and start again. Pour it through the strainer into a clean bottle. Put the grains straight into fresh soy milk, and put the bottle in the fridge.

What soy milk kefir looks and tastes like

• Colour and texture: pale yellow and a little thinner than milk kefir.
• Taste: tangy, with the soy flavour clear. Fermentation adds a fresh, slightly buttery note (study).
• Whey on top or at the bottom: soy milk kefir separates easily. Shake the bottle before you pour.
• Curds like tofu pudding: the kefir fermented a little long. Next time, strain it a few hours earlier or use a little less grain.
• Green, pink, red or black spots: throw away the kefir and the grains. Read Is the white layer on kefir mould?

The cow’s milk batch that keeps grains lively

• The rhythm: after about 6 batches in soy milk, make one batch in fresh cow’s milk. Then go back to soy milk.
• Why it helps: in a study that kept grains only in soy milk for four months, the grains became smaller and their bacteria changed (study). The cow’s milk batch gives them lactose and keeps them growing.
• Use your usual cow’s milk ratio for that batch, as in How to make kefir.
• Slow growth on soy milk is normal. If the grains stop fermenting cow’s milk too, read Are my kefir grains dead?

Coconut milk and oat milk

• Coconut milk: shake the jar gently once or twice, because the grains tend to sink (University of Guam).
• Every plant milk: give the grains the same cow’s milk batch after about 6 batches.

Storing soy milk kefir

• Up to 21 days in a sealed bottle: keep it closed in the fridge. It slowly gets sourer.
• Once opened, finish it within 3 days.
• Shake before drinking, because the whey separates in the fridge.

Kefir made without milk

Milk kefir grains live in cow’s milk, so they carry traces of milk into soy milk kefir. If you avoid milk completely, choose water kefir, which is made without milk.

• Make it at home: water kefir grains ferment sugar water. Use 60 g of sugar and 60 g of grains for every 1 litre of water. See our water kefir grains starter kit.
• Drink it ready-made: our water kefir is fermented with living water kefir grains.

Ferment your own, or drink ours.

Our live kefir grains come with a printed care guide, pH strips and help on LINE. Prefer it ready-made? Our soy milk kefir is fermented with living kefir grains in unsweetened soy milk.

Get live kefir grainsShop soy milk kefir

Frequently asked questions

Live kefir grainsSee them