Any idea about this weird pattern on the bottom of my boule?

Toast

Hi All, 

I did another high hydration SD by Maurizio today and although challenging I think it was fairly successful. But the pattern on the bottom really surprised me. Any ideas? On the advice of Abe, I'm posting the photo for your input and suggestions, etc. 

Here are some other shots - won't bore everyone with all the photos: Thanks everyone for all your support and encouragement on this incredible bread journey. So much to learn!

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Tartine 2 16 hrs later.jpg
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Tartine 2 Final bake 45 minutes.jpg
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Crumb shot Tartine 2 (1).jpg

Steam channels formed from escaping steam under the loaf, all those open holes of escaping hot gas setting the under crust as it escapes.  Most likely on parchment and/or dough surface wet under the loaf during the bake.  

Any prizes for the right guess?

Thanks for your reply! I wondered about that. I always use parchment but this dough was really wet - it was very moist when I took it out of the fridge, which is why I put some flour on top. First time for everything I guess. It it makes sense.

This is a challenge - but I don’t know if I could stick with it - ha ha - as it is a challenge to work with. Sticks like crazy! Now I’m looking at a spelt bread which again seems insanely hard to work with. 

as it is great but can make the dough very soft and elastic. I think this is why Trevor combines spelt flour with rye flour in his recipes. I saw a 50% spelt recipe and was tempted but for now try 50/50 wholewheat bread....and see what result I get with different wholewheat flour here in UK.... Kat

No idea, but that's a great crumb.  Well done.

There are a lot of large bubbles just under the surface. Did you puncture them before turning the dough out? That's my thought and jibes with Mini's comment.