In a large, non-metallic container, mix 100g unbleached all purpose flour, 100g room temperature water, and ½ teaspoon of active dry yeast until completely combined. No need to proof the yeast.
Either cover the container with a clean kitchen towel or transfer it to a glass or plastic container with at least 3 times the volume of the starter – it will grow! Do not seal airtight – your starter needs to breathe.
Set the starter in a warm spot, free of temperature swings, and drafts to ferment for 18 hours.
After 18 hours, stir down the bubbles and transfer 50 g of starter to a clean starter jar and feed it by mixing in 50 g warm water until mostly combined, then add 50 g unbleached all purpose flour and stir until completely combined.
Once the fed starter is fed, bubbly, and doubled in volume it's ready to use! This will take about 6-8 hours depending on your kitchen and starter.
Each feed transfer 50 g of starter to a clean starter jar and feed it by mixing in 50 g warm water until mostly combined, then add 50 g unbleached all purpose flour and stir until completely combined.
