Starter vs preferments
Hi, so I have some questions regarding the use of starters vs preferments. I understand the topic has been discussed at length on the forum, and I feel I've read through most of the threads, but still have questions.
To begin, I understand there's some confusion/misuse of the different terms.
As I understand it and use here, my starter is my "mother" starter that I keep in perpetuity at 1:1 ratio flour to water.
A preferment, to me, is when I take some of my ripe starter, mix with a % of the total flour and water in the final recipe and let it ferment before mixing with the final dough ingredients.
So, with these terms defined as such, my questions:
1) Most of the sourdough recipes I have followed and baked into successful loaves use around 20% (baker's percent) of the 1:1 starter, added directly to the final dough ingredients (+/- an autolyse of the water and flour before adding starter). By definition, using 20% starter leads to a 10% prefermented flour.
But I've seen on here many threads suggesting that 30% prefermented flour is ideal for a good rise. Some of these threads seem a little older, and I'm wondering if people are moving away from thinking this 30% prefermented flour is necessary.
2) Reinhart's San Francisco sourdough formula calls for a large firm intermediate build that is fermented for 4-5hrs and then cold retarded 12hr before mixing into the final dough. I think I calculated the prefermented flour at 40%. My understanding is that increasing the prefermented flour should lead to faster bulk fermentation, and possibly decreased sour. Yet this bread is one of the most sour I've baked. is it because of the cold retard of the firm intermediate levain?
And why would he chose such a large preferment? What other advantages can this convey to a bread?
3) I think I have more questions, but many would likely change based on the answers I get to these, so I'll hold back and see what people have to say.
It seems like the more I read the more confused I get!
Many thanks for your help.