In a very large glass bowl, combine water and sugar. Sprinkle with yeast, gently stir to moisten and let stand for 10 minutes.
Add sorghum flour and whisk until smooth.
Cover with a double layer of cheesecloth or a loose-fitting lid. Secure so that it is not touching the starter. Let stand at room temperature for 2 to 4 days, stirring 2 to 3 times a day. When ready to use, starter has as our smell, with small bubbles rising to the surface.
Store, loosely covered, in refrigerator until needed. If not used regularly, stir in 1 tsp granulated sugar every 10 days.