Hi everyone,
I'm experimenting with levain-based breads these days and one thing that is not clear to me is this: I have a starter. Now, how much of that should be used to make the levain mix?
Checking what Jeffery Hamelman says in his book "Bread" and what Maggie is saying in her book "artisan baking" I don't seem to get what the rules are. 
Hamelman seems to be using 20%, Maggie uses 17%, 20%....
So how do you figure that out? 
What about the rest of the percentages? like for water and flour? what determines those?

Also, if the bread you're making has a mix of different flour when would you use a mix in the levain or just say only one?

Your advice would be appreciated.
thanks
g