Ferment

Hi everyone,

I'm new here. I live south of Sydney, Australia. I'm new at baking. Made about a dozen bricks that no one would eat and then a dozen that are much better. Well at least they are eating them. I would like to make a ferment (hold back some dough) like Bertinet suggests in his book 'Dough'. At what stage do I pull out the extra 200g of dough? I use fresh yeast and hand knead. I am not making sourdough loaves yet. I want the starter as a white bread starter. Hope someone can steer me in the right direction.

Cheryl