Bread with natural yeast and stone ground flours

Ingredients

300 g (2 cups) durum wheat semolina "Tumminia"; 150 g (1 cup) common wheat  flour "type 1"*; 300 g (2 cups) lukewarm water; 150 g (1 cup) natural yeast (cream); 10 g Cervia salt
*serves to obtain a lighter bread. For a more tasty bread, but having a less fine grain,  replace the common flour with durum wheat flour.