I wanted to reference this old thread...
I have done it both ways. I have used real milk kefir grains to make my own kefir at home with ordinary cheap store bought pasteurized and homogenized whole milk, and it works fine, but I have found that the real kefir grains are very aggressive and will form curds and whey very quickly at warm temps (80 degrees F). I live in Phoenix, Arizona, and during the summer months, to cut down on energy costs, I keep my air conditioner set on 80. Anyways, at that temp, you will have curds and whey within about 12 to 18 hours, not 24 hours. And once it forms the curds and whey, it is very difficult to separate out the kefir grains from the curds.
In my experience, it was more trouble than it was worth, most of the time to bother real milk kefir grains. They do work, and if you want to stay on top of it, and make the process of making kefir one of your top priorities, and spend a lot of time and effort on it, then it is the way to go.
If you want to do it the easy way, just get some plain store bought kefir (Lifeway is easy to find, just make sure you use the plain, not the flavored style) and use it as the starter for some fresh milk. It's a lot easier, and it works about the same.
I suppose the other way of doing it is healthier, but I personally didn't notice a big difference in the way I felt. As long I drink some type of kefir every day, I feel fine.
I used to also make my own yogurt at home, and I got tired of doing it, too. I now just get the best store bought yogurt I can find-- the one with the most different cultures of bacteria. There is one that has 8 different cultures from Seattle (Cascade Fresh). And there is one from Colorado (Mountain High) that has almost as many and is available at most stores. I always try to get the one with the longest expiration date, and use it up quickly, so I get the best probiotic impact from it.
I do still make my own buttermilk at home. I use store bought buttermilk as the starter, and then I use whole milk or sometimes half and half, or even some heavy whipping cream to make a very tangy and tart sour cream like thing. It's great on potatoes.
I like the mesophilic cultures-- buttermilk and kefir. All I do is just fill a glass container 1/3 full of store bought cultured buttermilk or store bought kefir and then fill the rest of the container up with fresh cold milk right out of the fridge, and then put a cloth lid over it and let it sit out on the counter for 24 hours or so. It works perfectly, and is so easy. No straining out the grains. No heating up the milk before puting in a culture. No bothering with some sort of yogurt maker or crock pot to keep the milk warm.
I guess I got tired of all the extra time and effort involved. Making your own kefir at home from store bought kefir still has a lot of live and active bacteria. I think it's enough.
But if you are still interested in doing it the hard way, there are lots of places to buy milk kefir grains out there now. I got mine from the kefir lady and I also bought some from Amazon, they were recommended by the Dr. Oz show. They both worked fine, and ended up getting mixed together. I have them now in my fridge just sitting there waiting for me to reactivate them at some point in the future when I feel up to it again.