That’s a difficult question to give a definitive answer to. It’s a bit like asking how long is a piece of string.
The amount of flour set aside several hours earlier to ferment as a sourdough which at maturity we introduce into the bread dough can vary greatly depending on the characteristics of the bread we want to achieve or the nature of the time schedule we have to make our bread within.
All this may sound a little complicated but a good place to start is 25 -30% of the total flour weight be fermented as a sourdough.
Follow the formula below:
I hope that answers your question and gives you a starting place to make a basic loaf of sourdough bread.
Let me know how you go and if you have any further questions don’t hesitate to post them.