when to take "old dough" out of mixed ingredients
please can someone tell me when to take out a piece of dough to keep as "old dough"? i'm using Joe Ortiz' book "the village baker". in simple bread the ingredients are mixed, kneaded and left to rise for 2hrs, then kneaded a bit and left to rise for 45 min, then kneaded a bit, relaxed and left to rise for a 3rd time for 45 minutes and then baked. i'd like to keep some dough as an old dough starter but nowhere in the book does he say when to take a cup of dough out to keep. is it after the first 2hrs, the next 45 min or the final 45min? i'd appreciate any advice.