Basically, kefir is a natural and fermented probiotic much like yogurt, but yet very different in that it’s a much stronger probiotic than yogurt and has a much tangier taste (sour you wrote? … ok, sour it is). The probiotic was the active ingredient which healed your mouth so quickly and why I ‘preach’ on the fact that we should all be drinking it — all the time. It’s easy to make yourself if you purchase the ‘starter kits’ instead of the grains, which take a lot longer and in my opinion, quite a bit of time for a working, busy person who isn’t at home that much.
Making your own is usually cheaper as well as stronger in probiotics than the ready-to drink brands.
This is the type I use, a dependable brand, and as I said, really easy to make. The complete instructions come with the starter.