I've been running more experiments. Had some suprising failures. For example did one batch with 76% hydration and an 18 hour rise @ 70 degrees which should have been killer...yet crust was awful. Dense with a few huge bubbles. Go figure.
I had a very good batch today (picture below) and attribute it to a few changes in technique I'd like to share with the group.
I took a few hours to carefully read the summarized works of our learned brethren on the other side of the kitchen making sourdough. About 75% of the sourdough faq is directly applicable to our work with pizza. This should be required reading for anyone using starters with pizza: http://www.faqs.org/faqs/food/sourdough/faq/
(note, this page also gave me an ah-ha on the effects of hydration: http://www.artisanbakers.com/crumb.html
I made two key changes to this latest batch:
1) Added yeast only after autolyse, and added salt only at very end of kneading. The sourdough faq says that salt messes up the gluten structure, so adding it early can cause probelms. And of course the acidity from the starter may interfere with the autolyse process.
2) Took from starter at peak of yeast activity. Up until now I had been using starter without regard for the time since the last feeding. It could have been 2 hours, could have been 36 hours. Turns out by 36 hours most of your starter is dead and the bacteria concentration is abnormally higher than yeast. The time to take it is just before its peak, which can vary by starter culture but is probably sometime between 4-12 hours since the last feeding. You can time it fairly exactly if you use a 50% water, 50% flour by weight refresh mix, then observe the yeast activity via bubbles and height in the jar.
For this batch I did a 67% hydration dough, 21 hour rise @ 75 degrees. The dough felt just right. It was a coherent, jiggly, stretchable pillow of air. It stuck to things, but then un-adhered by slowly stretching then detaching by glutenous strands. I didn't overhandle it, but it was not averse to handling and did not disintegrate. It almost stretched itself out when lifted. I confess it was about 80%-90% of initial volume and could not have taken much more rise time before overblowing.
It turned out fantastic.