Whole Wheat Ciabatta

250g Poolish
250g Whole wheat
250g Bread flour
435g Water
20g Salt
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For the poolish:
125g Water
125g Bread flour
0.6g Fresh yeast
Mix all the ingredients for 5min until incorporated.
Transfer into a bowl (the polish will double in size, pick a bowl big enough) and let sit at room temp covered with plastic wrap for 6h then place in the fridge overnight.
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Next day:
Using a stand mixer with the hook attachment, add all the ingredients except the salt. 
Mix on low speed for 5min, add the salt and increase the speed (4-5 on a kitchen aid). Keep mixing for 10-15min or until the dough is smooth and elastic. Let the dough rest in the machine for 15min before taking it out. 
Transfer the dough on a lightly floured surface, give it a couple folds and place in a plastic container covered with a lid or plastic wrap to start bulk proofing. Keep the dough at room temperature for 3-4 hours (or until it doubles in size). Stretch and fold every hour. 
Transfer the proofed dough on a floured surface and shape into desired size loaves by flattening the entire dough with your hands and cutting it with the help of a dough scraper.
Let it proof for another hour before baking at 456F for 15-20min