Mix 1/2 c 100% whole wheat flour with enough warm (distilled) water to make a thick, porridge like mixture. Cover this mixture with a moist towel and let it rise on a draft-free warm location for 24 hours. You can double this recipe for your convenience and keep half of it in the refrigerator.
Day 2 and 3:
Stir the mixture 3 times a day.
Day 4 and 5:
Add 3 heaping tablespoons of 100% whole wheat flour and a bit of warm distilled water. Stir this mixture again 3 times daily.
The dough is ready when you see little bubbles coming from the mixture.