Fermentation science
Water Kefir and Milk Kefir: Different Grains, Different Drink
What separates the two cultures, which is more forgiving for a beginner, and why the grains cannot be swapped between them.
7 min read ·
What is the difference between water kefir and milk kefir grains?
They are two different symbiotic cultures that happen to share a name and a rough shape. Milk kefir grains are soft, irregular and white, like small cauliflower florets, held together by kefiran — a polysaccharide the bacteria in them secrete. Water kefir grains are firmer and translucent, closer in appearance to coarse sugar crystals than to curd.
Both are consortia of bacteria and yeasts rather than single organisms, and both reproduce by growing rather than by being replaced. But the populations differ, and each is adapted to the sugar it lives on: lactose in one case, sucrose in the other.
The drinks differ accordingly. Milk kefir is tart, thick and slightly effervescent, with a trace of alcohol. Water kefir is light, fizzy and mildly sweet, closer to a soft drink than to a dairy product.
Which one is safer for a beginner?
Both sit near the safe end of home fermentation, and the gap between them is small next to the gap between either of them and fermenting vegetables or meat. Both acidify quickly, and neither spends long in the low-acid window where things go wrong.
If pushed: milk kefir has the narrower margin in one specific way. It is a dairy product, so it should be made with pasteurised milk unless you have a considered reason otherwise, and it belongs in the fridge once it has set. Water kefir has no equivalent concern about its substrate.
The failure modes on both sides are mostly unpleasant rather than hazardous — over-fermentation making the drink harshly sour, or a neglected culture dying. The one thing to take seriously in both is bottle conditioning: a sealed bottle left warm for days builds genuinely dangerous pressure, and that is true of any carbonating ferment.
Which one is easier to keep alive?
Milk kefir, for most people. It is more forgiving of neglect, recovers from a stint in the fridge, and needs nothing but milk. If you can keep milk in the house you can keep milk kefir grains going indefinitely.
Water kefir asks for one thing that is easy to get wrong: minerals. Grains fed on refined white sugar and soft water weaken slowly and stop multiplying, because neither supplies what the culture needs. Unrefined sugar, a piece of dried fruit, a pinch of mineral-rich salt or hard tap water all address this, and which you choose matters less than that you choose something.
Water kefir also over-ferments faster in warm weather, and a batch left two days too long goes from lightly sweet to sharply acidic with very little middle ground.
Can I move my grains from one to the other?
No, and it is worth being flat about it because the internet is not. You will find instructions for converting milk kefir grains to water kefir. What happens in practice is that the grains stop multiplying and gradually break down, because the culture that built them is not the culture that thrives in sugar water.
You can ferment other liquids with either culture as a one-off — milk kefir grains in fruit juice, for instance — but the usual advice is to return the grains to their own medium afterwards to recover rather than keeping them there.
If you want both drinks, get both cultures. They are cheap, they multiply, and someone in a local fermentation group almost certainly has spares.