White sourodugh with potatoes and semolina

White sourodugh with potatoes and semolina

Recipe from

The crust has a bit of that semolina colour and crunch, and the crumb is very soft. Tender and tasty.

However I am not sure about the crumb structure. It has very big holes, but with the length of fermentation that went into it (around 10 hours total, at ~23C), I can’t believe it’s underproofed. Is it possible that such structure can be caused by going through a flat stage, and some central alveoli merging at that point?