I got a Chinese yogurt-making machine. Here is an example of what it looks like. I got the ACA VSN-15B but the 15A is almost the same and far more available (in Beijing). It cost about $20; the simpler VSN-15A costs about $10. You put 1000 ml of milk plus 50 ml yogurt starter (e.g., commercial yogurt) into a container and just start it. You can ferment it as long as you want. The instructions recommend 8-12 hours.
What interests me is (a) how easy it is and (b) the high quality of the result. I’ve made yogurt dozens of times without a special machine. It’s not hard, exactly, but it isn’t easy, either. You need to preheat the milk to denature the proteins, then let it cool before adding the starter. The denaturing phase takes a few hours and a different heating system (microwave oven) than the fermentation phase (ordinary oven). The final result isn’t as thick as I like unless I add milk powder — another not-quite-easy step. (Given problems with Chinese milk, I would never use Chinese milk powder.) Using the yogurt machine the texture is excellent (thick and creamy) without adding any milk powder. I suspect the final product is so much better because the proteins are more completely denatured. Maybe 2 hours at 150 degrees denatures a much larger fraction of the protein than 180 degrees for 5 minutes, for example. Another possibility is that I was using too much starter and that less starter produces better results. (How could that be? Perhaps with less starter you get more genetic diversity as it grows, which allows it to becomes better adapted to the particular milk and temperature you are using.) Perhaps a steadier temperature allows better adaptation to the temperature. You add hot water around the container to help steady the temperature.
I still need to experiment to get it as sour as I like but I can get it as thick as I want just by draining it. It’s not exactly the universal condiment but it’s close; tonight I had it on leftover dumplings.
All in all, a ten-fold improvement over what I’d done before. The big improvements: 1. So easy I can do smaller more frequent batches (in Berkeley I did at least 2 quarts at once), thus need less storage space. I also suspect the bacteria are more active soon after fermentation, so more frequent is better. 2. Requires much less attention. The mental cost of each batch is less. 3. Produces much better yogurt. 4. No more milk powder. 5. More energy efficient. (Using the microwave, I nearly boiled the milk, then heated an entire oven just to keep the yogurt warm while fermenting.)