Sourdough bread crumb ripped in two I've been trying my hand at sourdough bread for a few months now and it is getting better and better, but this keeps happening, and I have no idea what might be the cause:



My impression is that during the rise, the crumb tears into two pieces in the middle.

This is probably relevant: The dough is 80% hydration white bread flour, around 3 hours autolysis, then lamination and three stretches and folds spaced out. Altogether around six hours of bulk fermentation, overnight in the fridge (5&nbsp;°C), and baked in the morning on a pizza stone, with 250&nbsp;°C with steam for 20 minutes and 220&nbsp;°C for 20 minutes (the oven has the air convection turned on).

My problem is I have no idea which part of the recipe is to blame for the outcome, so I'm not even sure where I am deviating from the recipe I'm trying to copy (to be very exact, I'm trying to follow this one now: How To Make A Basic Open Crumb Sourdough Bread)

I'm not sure if this is important, but it also doesn't open up so well (but I don't have a proper lame, so I'm struggling with the scoring):
How much steam are you using? You might try baking the first 20 minutes in a french oven* (aka enameled dutch oven) and then take off the lid, but don't add extra steam. If you don't have a lame, use a razor blade or a really sharp boning knife (or a sharp paring knife can also do). 

This kind of problem can also be caused by underproofing, but it sounds like you're doing a good job there. Just make sure the bread doesn't spend too long proofing between your last fold and the fridge. 

Also, just based on the shape it looks like your dough maybe over-hydrated. 

*pre-heat the french oven and lid, though some people omit this step, drop in your bread, cover, bake for 20 minutes, then uncover and bake for 25-30 minutes longer.