This is the easiest way I know to preserve milk without refrigeration.
Mongolian "airag" may be the same thing.
I learned about kefir from Russians. They say "kee-fear", rolling the 'r' just a bit. Both syllables last a bit longer than you'd like and are accented equally.
Kefir will not "breed true" without a "mother". Also called "kefir grains".
That's a distinct colony which looks (and feels) like a little brain floating in the yogurty stuff.
You save and transfer it from batch to batch, like Kombucha.
The mother grows slowly from batch to batch. Kefir with no mother will not generate one.
The mother contains a diverse population of microbes that get along well. They can out-compete the wild organisms and don't need the milk scalded first.
Whereas yogurt needs to be held at certain heat to yogurtize properly, kefir can be brewed at room temperature or even saddlebag temperature.
One of the nice features of Kefir is that if it separates and settles, leaving clear whey, you can stir it up and it won't separate again. Yogurt by contrast will settle again.
My dad got a mother from Russian friends at his Orthodox church.
He's given me mothers a couple of times. Other Russian friends have given me mothers also.
I can't seem to keep them alive.
So there I was stranded with no starter. So I bought some commercial kefir, innoculated a kombucha mother with it, and have been using that to make "kefir" for a year and a half now.
It's a little bit different from purebred kefir, but the mother is much more durable.
If you have a real Kefir mother and want to know how to "operate" it, skip ahead to step 3.
If you only have dried mother grains, find the activation info elsewhere.