Whole milk is best. Store purchased, live, active culture yogurt (which is indicated on the container) will work as a starter. I place the jars in a large water-filled pot with a sous-vide cooker to maintain a warm even temperature overnight. (I forget the exact temperature I use). In the morning, I place the jars in the fridge and when I come home from work, voilà. I have great homemade yogurt. The consistency can be slightly runny. I've heard of people using emulsifiers to remedy this, but I don't bother.