Mix yeast and water in glass or plastic bowl. Let stand 10 minutes. Add 2 cups all-purpose flour. Stir again, cover. Keep in warm place 3 days, stirring once per day.
Gluten: Gluten is a protein found in specific grains (wheat, spelt, kamut, barley, rye). Other grains are naturally gluten-free but may have cross-contact with gluten-containing grains. Look for certified gluten-free products if you need to avoid gluten. Find out more about wheat and gluten substitutions.