I am sure you all make your own yogurt and are pros and all that--but I thought I would give you this link anyway. I started making my own yogurt awhile ago, but lately mine hasn't been turning out that great. I used the heat it on the stove, wrap it in a towel, and then let it sit overnight in the oven with the light on method. It worked beautifully at first but lately I couldn't get my yogurt to thicken up.
Well, I think I know why. I don't think I heated it up high enough, and then I didn't give it enough time to cool off before I added my yogurt (I use Greek Gods and I love it).
When I was web surfing the other day I found a blog post about crock-pot yogurt that was really helpful in explaining why you need to heat it and then why it needs to cool off. I made a batch of yogurt using this crockpot recipe yesterday and it turned out AMAZING. It was so thick and perfect. I took a cup out like she said and it is currently in my freezer, so I'll see how that works as a starter for my next batch. Awesome.