Mix 1/2 cup flour and 1/4 cup water in a clean glass or plastic container
Stir until no dry flour remains
Cover loosely with a lid or cloth
Leave at room temperature for 24 hours
Discard half of the mixture
Add 1/2 cup flour and 1/4 cup water
Stir well and cover loosely
Repeat feeding once daily
Keep discarding half before each feeding
Continue for 5 to 14 days
Use when it is bubbly, rises after feeding, and smells pleasantly sour