I have been making yogurt of various kinds at home in SCD style since my DD was around 2. She is now 11. Over the years, I've tried different ways to make yogurt, such as various yogurt maker, warm water in cooler, using a heating pad, etc. And, I want to share the latest "Method" that works for me at current life-style.
Until recently, I made a gallon of cow's milk yogurt and gallon and a half of goat milk yogurt at once in my oven. (Cow's milk yogurt is for me and my husband, the goat milk's is for my 2 kids.) It worked well, but I had to plan my baking days around it to incubate the milk for 24hrs. which was inconvenient.
It seems every oven has different temp. settings. Some people had good luck by changing the light bulb inside, to rise the temp in the oven (with a door cracked open to keep the lights on.) Lucky me, my oven could be set as low as 100F, and keep it running for 12hrs. at a time. I just had to re-start my oven after 12hr. (to incubate for 24hr.) but that wasn't too much of a trouble.
One of the clue to make a good yogurt is the temperature. You need to avoid thermal shock when you add the starter in the milk. And you have to incubate in a low, steady temp., undisturbed. (Too hot of temp will kill the culture, and burns the yogurt on the bottom, especially when you incubate it for 24hrs.)
Warm water doesn't stay warm enough in cooler, and my heating pad doesn't stay on continuously: It turns itself off quietly, so, keeping the temp steady is difficult with it. Most yogurt maker is too hot for the kind of yogurt I want to make, and I can't make a big batch all at once in yogurt maker. And, I don't have double oven.
Then, I had an idea of using heating rock from pet store. You know, for lizards and snakes. It keeps the low, steady temperature as long as you keep it plugged, and most stays around 90-110F. So, I put the heating rock on the bottom of a cooler; use 4 small cups around the heating rock to put a small baking sheet on top, then, prepared milk on the baking sheet. I put a bath towel on top of the lid of the yogurt pan, and a cooking thermometer to check and control the temp in the cooler.
I'm happy : )
I can only make half gallon at a time in the cooler, but it frees my oven this way, and I like the convenience of having my oven available anytime. The only concern is that my DD with a smile on her face, with a though of getting a pet snake is a step closer....
P.S. If any one is wondering about the SCD, it is based on the book "Breaking the Vicious Cycle" by Elaine Gottschall. Their main website is Pecanbread dot com.