Whisk all-purpose flour, whole wheat flour, wheat cereal mix, salt, and yeast together in a large bowl. Pour in water; stir until well blended. Cover bowl with plastic wrap and let dough rest at room temperature, 12 to 18 hours.
Push dough gently to deflate; form into a ball. Transfer to a bread pan. Let dough rest, 2 to 4 hours.
Preheat oven to 425 degrees F (220 degrees C). Make a 1/2-inch cut in the top of the dough.
Bake in the preheated oven until crust is well-browned, about 45 minutes.