Sourdough Starter Begun from Flour and Water, and Dried for Keeping

A sourdough starter needs nothing but flour and water: mixed and kept warm, it is colonised by wild yeast and lactobacilli from the flour, the water and the air. Feed it every day for a week or two until it bubbles and a spoonful floats in water. Dry a portion thin to keep as a starter culture. The picture: a bubbly sourdough starter.