I have never been successful in fermenting dosa batter properly in the US. I generally soak urad dal, rice and fenugreek seeds for a few hours and grind them together. Even if I leave the batter in 30°C temperature, the batter does not double in volume, as is generally does in India. The batter seems to ferment somewhat because of the sour taste but it seems that the fermentation is not being done by the "right" microorganisms.

Any ideas on improving fermentation, or on mimicking the process they use in India?