I have been experimenting with yogurt and got my process down to how I like my yogurt. Here's what I do.
1. Heat milk to ~185 in a make shift double boiler, turn off heat and let sit covered for 30 minutes. I have found that the longer it sits at 180-190, the thicker/creamier the yogurt will come out.
2. Cool milk to 110 in a cool water bath in the sink, lightly mixing it with a whisk to cool quicker, trying not to make it too frothy.
3. Pitch yogurt with active live cultures. I use 3-4 TBSP of yogurt (straight out of the fridge or allowed to warm to room temperature) per 1/2 gallon of milk and whisk it into the milk thoroughly. I prefer starting with Stonyfield Oikos Greek yogurt but then use my own yogurt as a starter.
4. I pour the milk and culture mixture into the storage jars, cover, and let them sit at ~110 for 7 hours to produce the taste I like. The longer they sit, the more tart it becomes.
5. I then loosen the lid and place in the fridge to cool.
I have done this with whole milk and 1%. Whole milk has produced a slightly creamier yogurt with less liquid (whey) that separates from the yogurt, but I have only been using 1% milk lately. I'll have more whey, some of it I pour out, some of it I stir back in. Either way, this yogurt is tastier than commercial yogurt and we have been eating much more yogurt at home. I'll make 1/2 gallon every week or week and half.