When I think of it (especially now that it is peach season here) I'll take a little container of whatever natural yogurt I can find, heat up a quart of whole milk a little bit, mix it into the yogurt, and leave it out wrapped in a towel for a while.

When you get close to running out, just use some of the old to make more.

For some reason I find it to taste better than anything I can just purchase. I recommend giving it a try.