"Kefir is a fermented milk beverage that contains beneficial probiotics that may help give your immune system a boost, among other health benefits. One of the best and least expensive ways to get healthy bacteria through your diet is actually to obtain raw milk and convert it to kefir yourself. All you need is one-half packet of kefir starter granules in a quart of raw milk, which you leave at room temperature overnight. By the time you wake up in the morning you will likely have kefir. If it hasn't obtained the consistency of yogurt you might want to set it out a bit longer and then store it in the fridge.
A quart of kefir has far more active bacteria than you can possibly purchase in any probiotic supplement, and it is very economical as you can reuse the kefir from the original quart of milk about 10 times before you need to start a new culture pack. Just one starter package of kefir granules can convert about 50 gallons of milk to kefir. This is also a far healthier, and far more economical, way to nourish your body with probiotics than buying any of the commercial probiotic beverages on the market, as these typically contain added sugars and are made using pasteurized milk, which I don't recommend drinking."
There's more information on Dr. Mercola's site about kefir, recipes, etc.
I have friends who make their own kefir regularly, and they will tell you what a difference it has made for their health! It has been especially beneficial for their children who have a lot of health challenges.
If you want/need a non-dairy option, you can also make kefir using water. Here's a simple video on how to make your own water kefir.
Here's an article about different kinds of kefir grains and where you can find them. You can order kefir grains online or sometimes you can find them locally, from a friend or a farm nearby.
I realize that not everyone is able to tolerate fermented foods. (I'm finally able to eat yogurt again, but I haven't managed kefir yet.) But if you can, then kefir and other fermented foods can be a great addition to a healthy diet and a valuable tool for improving health.
I hope this information is helpful. Please share any great tips or resources about kefir that you have in the comments. Thanks!