Emmanuel Hadjiandreou, How to make Bread, London: Ryland Peters & Small, 2011. P11.
"Sourdough.
Wheat Rye and other grains have been combined with water by bakers for thousands of years to make sourdough starters. Wild yeast spores are present in air and flour. Mixing Flour and Water and allowing it to ferment - i.e. when yeast breeds and produces Carbon Dioxide - creates a starter (also known as the 'Chef' or 'mother'). The starter takes 3-5 days to develop and, when it is ready, can be used (in place of yeast) to make bread.
Day 1:
Take 1: mix 1 Teaspoon of Flour and 2 Teaspoons of Water in a clear jar. Seal and let stand overnight.
Day 2, 3, 4 and 5:
Add 1 Teaspoon of Flour and add 2 Teaspoons of Water to the jar and stir. More and more bubbles will form on the surface.
To make a starter: mix 15g/ 1 tablespoon from the jar with 150g/ 1 generous cup flour and 150g/150ml/ 2/3 cup warm water in a large bowl. Cover and let ferment overnight. The next day use the amount of starter needed for your recipe.
Add 1 teaspoon flour to the remaining ferment in the jar, seal and refrigerate for use another time. If it is left in the refrigerator for a long time, it might become dormant. Throw away the acidic liquid on the surface, stir in 30g/2 tablespoons flour and 30g/30ml/ 2 tablespoons water, mix to a paste, seal and let stand overnight. The next day, if bubbles have formed, it is ready to be made in a starter. If not repeat the process above. Treat your sourdough with tender loving care and you can keep it indefinitely."