Wash and soak each of the each kind of rice and the lentils overnight or for 8 hours, separately.
Then grind all the three together to a fine paste with the coconut milk.
Put the dry yeast in a bowl with sugar and 3 tablespoons warm water.
When it froths, add it to the ground batter.
Add salt to taste and keep aside for 5 hours till it doubles in quantity.
Get the steaming vessel ready on medium flame with the required amount of water in it.
Put a tablespoonful of the batter into each of the moulds/ aluminuim bowls and steam on medium heat till the sannas are fluffy and done right through (around 15 mins) or when a skewer pierced into one comes out clean.
All of them may not go into the steamer in one round so do them in batches.