Sure, you can make sourdough bread with store-bought yeast. But you can also make your own sourdough starter, making use of unique wild yeast floating around in your kitchen—and especially in the flour itself. A sourdough starter serves the same function store-bought yeast would, but gives your bread a unique flavor by utilizing that wild yeast available all around you.

Wild yeast spores and lactic-acid bacteria are airborne all around you and are ever-present in flour. Making your own sourdough starter is as simple as combining flour (unsterilized, grain-based flour is best for the most amount of wild yeast spores) and water and leaving the mix covered for a week, creating ideal conditions for those airborne spores and bacteria to multiply.

Mix flour and water together, cover it with a cheesecloth of coffee filter and rubber band to keep bugs and dust out, and wait a week for the microorganisms to colonize your container and begin the fermentation process. Mix at least once daily. After a couple of days, when it begins bubbling, you should feed it a few table spoons of flour to keep it going.