Cover with a clean dish towel and leave it on the counter. I kept mine in my kitchen bay window so it was warmed by the sun.
3x a day, add 2 tablespoons of flour and ¼ cup water. You want the consistency to be like runny pancake batter so feel free to use more water if the starter needs it. Some gluten free flours need more liquid so go by the water feel of the starter.
By day 3-5 your starter mix should be bubbly and smell sour.
Add your starter to the bread mix:
2 cups gluten free flour blend (*see note) 1 ½ tsp Kosher salt ½ c sourdough starter (see post for directions to make this) water by feel
Mix well and set out to rise for 12-24 hours. Congratulations! This is your starter. See my gluten free sourdough bread recipe linked in this article for the bread recipe to use your starter with.
I have used sorghum, brown rice, and millet flours successfully. I also have used King Arthur Measure for Measure GF Blend, Bob's Red Mill 1 to 1 GF Blend, and GF Jules gluten free flour blends to make a successful starter.
I found my starter really likes brown rice flour and it bubbles really well using it.
In order to give your natural yeast a chance, I highly recommend using purified water. Chlorine in tap water can kill your yeast, making your starter not grow.