Uneven oven spring in sourdough boules
Folks, I've been baking sourdough boules pretty much weekly since March, and have been happy in general with the results (sometimes great oven spring, crumb, and texture). However, I have been plagued by an occasional boule that seems "flattened" on one side compared to the other. This has happened when there was absolutely *nothing* different from the times I have had great results, and there's no obvious attributable cause. So, I was hoping that someone here might have had the same issue and could point me to something I'm overlooking.
I do 700g flour (625 bread + 75 whole wheat) to 525 g water. I combine starter with 475 g of the water then add flour, and autolyze (without salt) for 60 minutes. Add in the salt (dissolved in 50 g of the water) and BF with stretch and folds for 2.5 hours (until dough passes windowpane test) and then for an additional 2.5 hours (until it has risen by 1/3 volume, I can see bubbles forming on the top and bottom, and it "wobbles" when gently rocked). The dough temperature throughout this process remains at about 78 degrees.
I shape in the usual way, gathering the dough on the bottom and flipping over then rolling the boule downwards gently with my top hand and rotating until all the way around. 20 minute bench rest, final shaping, then overnight proofing in the fridge.
The starter was in excellent shape; in the feed before I made my levain it had tripled. What on earth gives?