If you want to learn more about how to make your own fermented foods, including kefir, the subject covered very thoroughly in this book:

http://www.amazon.com/dp/1931498237
Wild Fermentation: The Flavor, Nutrition, and Craft of Live-Culture Foods
by Sandor Ellix Katz

I keep saying I'm going to make almond or soy milk yogurt one of these days, but have never gotten around to it. I do brew beer but the type I make is not supposed to contain any bacteria, but only one species of yeast, which provides lots of B vitamins, but I don't believe it's particularly good for the gut.
Ron