Top Crust Separates from Crumb
I've seen a number of posts on this topic but the answers range from vague to contradictory. I'll try to be as specific as I can to allow for more precise answers.
I'm a fairly experienced homebaker although new at sourdough breads. I'm using Chad Robertson's (Tartine) Country Bread recipe and have baked about 8 loafs so far. They've been getting better and better as I bake but there is invariably a trait in all these loafs (which by the way, never saw in my yeasted breads) and which is the subject of this post. The crust separation's extent ranges from almost imperceptible to flat out obvious and although my most recent loaves showed less of this problem, my last loaf pictured here has noticeable separation.
This is a 90%/10% white/whole wheat dough hydrated at 75%. The dough weighs approx. 1.75 Kg
Bulk fermentation: ~ 12hrs @ 68-70 degrees
Shaping uses minimal flour addition
Proofing: 4hrs @ 75 degrees
Oven spring is ~ 100% of initial height ans oven is steamed for first 10min. approx. Gas oven starts at 500 F for 10min. then 450 F and down for 35min. Loaf is baked on stone at mid height. Steam is created with cast iron/lava rocks on bottom rack.
Taste and crumb texture is excellent (so I've heard :))
Any help is greatly appreciated and please try to be specific.