I make yogurt with a yogurt maker and the yogurt is nice and thick, but it is very sour at the top only and the rest is almost sweet, like a sweet fresh cheese. Why isn't it sour all over?  This is how I prepare it:   heat 1l (goat or sheep) milk slowly (1h) to 85° Celsius, keep it at 85° Celsius for 10 minutes, let it cool slowly to 45° Celsius, mix well with 50g simple yogurt, put it in the yogurt maker at 45° Celsius for 12h.  
What I normally do is fluff up the rice- sometimes its just the top layer which is a little more moist due to condensation, but if it's watery I sometimes leave the rice cooker open for a bit and let it evaporate which works for me (although I don't know if that is how you're supposed to do it)  