Yeast is difficult to make reliably at home from scratch
Use a sourdough starter as a natural yeast substitute
Mix equal parts flour and water in a clean jar
Stir until smooth
Cover loosely with a cloth or lid
Leave at room temperature
Feed daily with equal parts flour and water
Keep feeding until it becomes bubbly and active
Use the bubbly starter in place of yeast for baking
Store the starter in the refrigerator when not in use
Refresh it with flour and water before baking