Wash the white rice and soak the white rice in enough water for at least 5 to 6 hours.
Grind the white rice smoothly using a food processor or a good quality blender with just enough water to make the batter.
Add the grated coconut and grind or blend the contents again until the coconut is well blended with the rice batter.
Add the cooked rice also the contents and grind or blend until the mixture is smooth.
Add enough water in case the water is less so you can make the perfect batter for making the Kerala style rice pancakes. The consistency of the batter should be like the consistency of dosa batter or a little more liquid like consistency than regular pancake batters. If the batter is too thin or too thick, the pancakes or vellayappam may not come right.
Transfer the batter to a good quality large container (the batter will rise) with enough space to hold the batter as it will rise.
Add enough salt and mix the contents well.
Dissolve the dry yeast in very little water that is slightly warm.
Add sugar to the yeast mixture, gently mix and keep it closed for about 10 minutes.
After about 10 minutes, you can see that the yeast has dissolved and the yeast mixture has become bubbly.
Add this yeast mixture to the batter and mix the contents well.
Keep the contents closed for fermentation for another 8 to 10 hours or until the batter is fermented well. The batter will get better if you keep it for fermentation for a few more hours.
The batter will get fermented naturally and rise under normal situations. However if is too cold, you may turn on the heater for a few minutes which will help the batter to rise. Also, if you are in colder places, it may take more hours for the batter to get fermented and rise. Just make sure that you don't keep in cold places (by turning on the heater to regulate the temperature inside the room or by covering the container with thick blankets or you may also keep the container inside the oven with just the light on for some time) and give enough hours for the batter to rise naturally.
Once the batter is fermented, you can see that tiny bubbles have formed in the batter and the batter has risen. Gently mix the contents and now the pancake batter is ready to be used!