Dissolve the yeast in the warm water in a sterilized glass jar or crock. Allow to become bubbly, stir in the brown rice flour and brown sugar. Cover and allow to stand overnight.
The next morning stir down the starter with a wooden spoon and if the mixture is very thin stir in an additional 1/2 cup flour and 1 teaspoon sugar. Stir several times throughout the day.
After 24 hours the mixture should have a slight sour odor. The starter can be used at this point.
When feeding the starter use these guidelines: If using 1 cup of the starter, feed remaining starter with 1 cup of flour, 1 teaspoon brown sugar and filtered water. I like my starter a little on the thick side.
Starter should be fed weekly and may be kept in the refrigerator between feedings.