If you want natural yeast for yogurt, use hot milk insteady of water and flour. After 1 day, you will get small amount of yogurt particles. Collect them to make bigger particles. By using small yogurt particles, add new 1 cup of hot milk and powder of chickpeas and keep it warm by a blanket. 1 day after, you will get bigger yogurt yeast. If you think it is enough to make big yogurt use it. or repeat the process.