Idlis and I share a love-hate relationship... used to hate them once but I love them now. I always took them for granted because we had 'em for breakfast almost everyday of the week. Never knew how making them wasn't as simple as grinding rice and dhal, mixing, fermenting and steaming... there are quite a few intricacies and tips that i had failed to observe, which resulted in flat, not so soft idlis initially. Over the years, i've learnt: to use the right variety of rice, the importance of the grinding time, how much water to add, methods to facilitate fermentation and so on. Though my idlis are still no match for my paati's (who still uses the whole black urad dal and painstakingly washes them in several changes of water after soaking), I think they are quite good and soft.
Ponni Boiled Rice/Idli Rice - 4 cups (I replace 1 cup of this with rosematta rice)
Whole urad dhal (white) - 1 cup
Fenugreek seeds (methi/vendhayam) - 1 heaped tsp
Salt, to taste (I have a measurement for this but it involves my right hand so not much help to others) :)
1) Soak rice and methi seeds together for atleast 4 hours. Soak Urad dhal separately for about an hour.
2) Drain and Grind Urad dhal (I use an ultra grind and these measurements may not hold good if you are using a mixie) until soft and fluffy (almost 30-40 minutes). I don't add too much water after the initial stage and just a little bit after about 10-15 minutes. You will observe that the batter rises up quite a bit within 20 minutes. Empty this out to a big container (preferably stainless steel).
3) Next, drain and grind the rice and methi mixture for about 20-25 minutes. It'll be slightly grainy to the touch. Grind it for additional time if you want it to be very smooth. The texture of the idlis varies a bit because of this and it's a personal preference. Empty this batter into the same big container used for the urad dhal.
4) Add the required amount of salt and mix both these batters well by hand. The consistency shouldn't be too thick or thin but pourable. Cover and allow to ferment in a warm place for 12 hours or even more during the winter. I put it in the oven, switch on the oven light and keep it on overnight. If it has fermented well, you will see that the batter has risen and looks porous with small bubbles.
5) Refrigerate this for a few hours before pouring into greased idli moulds and steaming them for about 10 minutes.
6) Soft, spongy idlis are now ready to be eaten with Sambhar, Tomato Kurma, Chutney or Milagai Podi.