I thought I’d make this page with my findings, without the story.
There are plenty of pages in the web that show you how to make yogurt at home. They all share the same steps:
Scald the milk and let it cool.
Introduce the culture in the milk, either from yogurt, or freeze-dried.
Keep the milk at a steady temperature for several hours (8 to 24), either in a yogurt maker or in an tricked out oven.
For me, step 1 has always seemed annoying. Scalding the milk is the most labor-intensive step, and it requires vigilance to make sure the milk doesn’t burn. Also, almost all sets of instructions on yogurt recommend that you get milk that is not ultra-pasteurized. Many recommend raw milk. But, scalding the milk at home is actually harsher than ultra-pasteurization. To me this is cognitive dissonance.
Making yogurt without scalding the milk
If you try to make yogurt without scalding the milk, using regular, non-ultra-pasteurized milk and a regular yogurt maker, you will probably find that your yogurt leaks whey, which gives it a bad taste and a bad texture.
There are two ways of getting good taste and texture out of un-scalded milk (there may be more but these are the ones I found).
Use ultra-pasteurized milk: I use Organic Valley. The texture and taste are great. I don’t understand all those complaints against ultra-pasteurized milk. Some people have problems digesting pasteurized milk, it is true. But for the rest of us, ultra-pasteurized is a very good milk for yogurt. Let me stress: home scalding is harsher than industrial pasteurization (if Harold McGee’s tables in On Food and Cooking are accurate)
Control incubation temperature: The bacilli in yogurt thrive mainly in a range of temperatures: 90-110F, or 32-43C. On the hot end of the range, the fermentation is fastest, but it produces a coarse grid that leaks whey. On the cold end of the range, the fermentation is slowest, but it produces a finer texture that traps whey. If you manage to get the incubation temperature down to 90-95F, the texture of your yogurt will improve, and they whey may disappear completely.
How to control incubation temperature
Commercial yogurt makers don’t offer control over incubation temperature. I know two ways around this:
Use a food dehydrator instead. These can go down to 95F.
Get an external temperature regulator. This is a gadget that you plug to the power outlet. You plug the yogurt maker to the gadget. The gadget has a temperature probe that you stick inside the yogurt or (how I do it) inside a cup with water inside the yogurt maker. It is then programmed to shut the yogurt maker off when the temperature reaches X, and turn it on again when the temperature is lower.
The one I know is the Johnson Controls model A419. You can get it here.