What is kefir and what can I use in its place?

Kefir is a fermented milk drink that has a tang, or sour flavor, similar to yogurt. Look for it in the dairy section of the supermarket near the yogurt. Replace it with yogurt thinned with milk. If you need 1 cup of kefir, use 3/4 cup of plain yogurt thinned with 1/4 cup milk.