Soak the idli rice, urad dal, and methi in a bowl for 4-6 hours. you can also soak them in a separate bowl. Soaking makes the grains soft and plumped up. It's then ready for the next step, grinding.
1¼ cup Urad Dal, 4 cups rice (idli rice), 1 teaspoon methi seeds
Blend the soaked grains with just enough water to get the right consistency of the batter. If you are living in cold climates, use warm water to blend the grains. This helps in making a fine and fluffy rice batter.
Transfer the batter into a large bowl. Keep in mind that that batter doubles in volume as it ferments. So be sure to use a sufficiently large bowl to mix the batter.
Leave the batter covered in a warm place (but not high heat) to ferment for anywhere between 8-12 hours.
The time depends on room temperature. The warmer it is, the faster it ferments. This is the most important step in getting proper fermentation and the perfect idli batter.
During cold weather, I place my idli batter in a relatively warm place like the oven and leave the oven light on to raise the temperature. with the light on.
After 8-12 hours, you will notice that the batter has risen considerably. Add rock salt, sea salt, or table salt to the batter and mix evenly.
You will also notice that the rice batter is more fluffy and thick after fermentation. Add a cup of water if required.