Denser crumb towards centre of bread
Sorry if this is the wrong place to ask, but there's a problem I've been having lately with bread I bake. I'm using this schedule:
Friday 8-10pm: feed rye starter
Saturday 8am: mix leaven (20g rye starter, 100g water @30C, 100g flour)
8-12 hours later: mix dough: 150g leaven, 300g water @32C, 400g strong white flour, 25g wholemeal flour, 10g salt.
Apply three stretch and folds over first 2h 30; bulk for 3-3h30 total.
After bulk, shape and then prove for an hour before putting in the fridge overnight
Sunday morning: bake in a dutch oven at 250C for 15 minutes, then 230C for another 25-30 minutes (covered for the first 25 minutes).
This produces bread that tastes great but has that slightly gummy and moist touch to it. I also see that it has a much more open crumb towards the bottom and outside of the loaf - which I confirmed in the end by slicing a boule in half horizontally and seeing a more open crumb on the outside. Below a re a couple of vertical photos showing a more open crumb away from the centre and a more dense one towards the middle:
What are the most likely causes of this? I always hear underproofing metnioned as the big culprit, but the dough seems to past the dent test before I put it in the fridge. Are there other ways to test proofing/is something else going on?