Warm the beer until tepid, crumble in the yeast, and rest for 15 minutes.
Stir in the rye flour and yoghurt, then set aside for 24 hours.
Mix caraway seeds, treacle, salt, and olive oil into the bubbly starter.
Add white flour and knead in a mixer or by hand for 10 minutes until elastic.
Place dough in an oiled bowl, cover, and let rise for one hour until doubled.
Preheat oven to 210°C and grease two baking trays with oil and polenta.
Shape dough into two round loaves, score the tops, brush with egg, and dust with polenta.
Bake for 40 to 50 minutes with a tray of water in the oven for steam.