Mix flour and water to make a thick paste
Cover loosely and leave at room temperature
Let natural yeast and bacteria develop over several days
Feed the mixture daily with fresh flour and water
Keep it warm and clean
Wait until it becomes bubbly and rises reliably
Use the active starter as baker’s yeast substitute
To make a commercial-style yeast culture, grow a pure yeast strain in a sterile sugar solution
Aerate the culture while it multiplies
Harvest the yeast cells by settling or filtering
Wash and press the yeast into a paste
Shape, dry, or refrigerate the yeast for storage