I lowered the temperature and now it coagulates. Yippee!
However, it turns out super-grainy, almost like curds & whey. I wonder why... I only incubated for about 5 hours, although now I regret that I didn't check it earlier, this may be due to overincubation, or not?
The super-grainy stuff still doesn't seem very thick, but then again, the separated curds cannot be properly compared to creamy yoghurt...
I'm thinking of trying two things:
1. trying to control the temperature even better: I would think that curd separation would be due to too high temperature, rather than too low? I'm afraid my yoghurt might have gone up to 45 celsius, even I was aiming for 42. After all, my oven isn't that precise and I had to turn the temperature up and down all the time to keep between 40-45.
2. adding a bit of powdered milk for thickness. Maybe this would help me achieve the proper thickness before it gets too sour and separates the curds? although it didn't taste super-sour, and as I said, it was only 5 hours. but still. at least it could help the thickness issue.
Oh, and I forgot to say in the beginning that I heat it to 185 celsius for 20mins at first. Although almost every time I mess that up and boil it at some point.