Kefir

Kefir is a cultured and microbial-rich food with natural antibiotic properties that restores the ecology of the digestive tract. It contains beneficial bacteria and yeast, and is made from milk. It is similar to a drink style of yogurt, but more tart and contains different microorganisms. It does not feed yeast and typically doesn't bother people who are lactose intolerant. Kefir is made from grains that contain the beneficial yeast/bacteria that clump together with the milk proteins (casein).
The following is a recipe from the book Nourishing Traditions by Sally Fallon, further sources can be found at the Weston A. Price Foundation (http://www.westonaprice.org/). It's a great cookbook source that bucks the trend of modern dieticians.

Makes 2 cups
2 cups fresh whole milk, nonhomgenized and preferably raw
1/2 cup good quality cream (optional)
1 tablespoon kefir grains or 1 package kefir powder (can find sources on internet)

Place kefir grains in a fine strainer and rinse with filtered water. Place milk and optional cream in a clean wide-mouth, quart size mason jar. Milk should be at room temperature. Add kefir grains or powder to milk, stir well and cover loosely with a cloth. Place in a warm place (65-76 degrees) for 12 hours to 2 days. When the kefir reaches a tartness you desire, the kefir is ready.
Pour the kefir through a strainer into another jar and refrigerate. Use the collected kefir grains to start another batch.
Raw milk in the Phoenix area can be found at http://www.saveyourdairy.com/ in Queen Creek.