my process:
75 g active starter
400 g water
500 g flour
11 g salt
mix all ingredients together and let rest 30 minutes before doing 4 rounds of stretch and folds, each 30 minutes a part.
bulk ferment at room temp overnight (7-9 hours)
preshape, let rest for 30 minutes, final shape and transfer to banneton, proof one hour at room temp and then move to fridge for 24-48 hours
Preheat dutch oven at 500F for 30 minutes, score dough and then transfer to dutch oven with 3-4 ice cubes. Bake for 30 minutes at 450F and then take the lid off the dutch oven and cook for an additional 10 minutes at 400F. Take boule out of dutch oven/remove parchment paper and bake on rack for a final five minutes at 400F before cooling slowly with the oven ajar.
Actually, that looks pretty good. You have a good distribution of holes at a variety of sizes, and it "looks" light and airy. That said, you asked for ways to improve it, so I'll offer a couple of observations that you can consider.
First, you don't mention what kind of flour you are using or what your room termperature is, but are you certain the dough is standing up to a 7-9 hour bulk ferment? Over-fermentation during bulk will make the dough sluggish later during proofing. Maybe try shortening your bulk fermentation to the point where your dough has developed good aeration in the bucket, with many small and a few larger bubbles visible through the sides/on the top.
Second, even though you have fairly open crumb, the loaf has a pretty low/flat profile, and "flow" in the loaf looks pretty horizontal. It looks as if the loaf is expanding outward rather than upward, making the holes wide and flat rather than taller and rounder. Do you put enough dough in your banneton for the size?
Third, (and perhaps something to try first): You don't mention giving your loaves any bench time after you remove them from the fridge before baking. I use a similar process, and I give loaves about 45 minutes on the bench in the kitchen before putting them in the oven. It improved my results over baking straight from the fridge . Many bakers do it your way, and I'd guess many also do it the way I do. You'll have to figure out what gives you the best result with your dough in your oven in your kitchen.
Just my 2 cents worth! I hope it at least gets you thinking and experimenting.
Best of luck
OldWoodenSpoon
get two opinions ;), but i was going to suggest seeing if pushing bulk ferment farther would open up the crumb more. it is already pretty open, but it doesn’t look overproofed to me. for that % pre-fermented flour, i often bulk for 12-16 hours. temperature will of course matter, a lot, and you don’t give details of yours. for me, low-70’s is the 12 hours and i need 16 if we’re in the low 60’s.
so: if you try all of oldwoodenspoon’s suggestions and still want to try one more, you could try bulk fermenting longer. :)
-c