Make and ferment the poolish: Combine the water and yeast in a medium bowl. Let stand 1 minute, then stir with a wooden spoon until yeast is dissolved. Add the flour and stir until the consistency of a thick batter. Continue stirring for about 100 strokes or until the strands of gluten come off the spoon when you press the back of the spoon against the bowl. Scrape down the sides of the bowl with a rubber spatula. Cover with a clean damp towel or plastic wrap and put in a moderately warm, draft-free place until it doubles in volume.
Mix and knead the final dough: Measure the remaining ingredients. Measure and transfer 1 cup (9 ounces) of the poolish into a 6-quart bowl. (Discard remaining poolish) Add the water and yeast. Break the poolish up well with a wooden spoon and stir until it loosens and the mixture foams slightly. Add 1 cup of the flour and stir until well combined. Add the salt and only enough of the remaining flour to make a thick mass that is difficult to stir. Turn out onto a well-floured surface. Knead, adding more flour as needed, until the dough is soft and smooth, 15 to 17 minutes total. The dough is ready when a little dough pulled from the mass springs back quickly.
Ferment the dough: Shape the dough into a ball and let it rest on a lightly floured surface while you scrape, clean, and lightly oil the large bowl. Place the dough in the bowl and turn once to coat with oil. Take the dough's temperature: the ideal is 78 degrees. Cover with a clean damp towel or plastic wrap and put in a moderately warm (74 to 80 degrees) draft-free place until doubled in volume, and a slight indentation remains after pressing a finger into the dough.
Divide the dough and rest: Deflate the dough by pushing down in the center and pulling up on the sides. Transfer the dough to a lightly floured work surface and knead briefly. Cut into 4 equal pieces. Flatten each with the heel of your hand and shape into a tight ball. Cover with a clean damp towel or plastic wrap and put in a moderately warm draft-free place for 30 minutes.
Shape the dough into loaves: Flatten each with the heel of your hand on an unfloured board. Shape each into a 14-inch loaf.
Proof the loaves: Place the loaves seam side up in a well-floured couche. Cover with a clean damp towel or plastic wrap and put in a moderately warm draft-free place until increased in volume about 1 1/2 times, or until a slight indentation remains when the dough is pressed with a fingertip.
Bake the loaves: 45 minutes to 1 hour before baking, preheat the oven and homemade hearth or baking stone on the center rack of the oven to 450 degrees. The oven rack must be in the center of the oven. Gently roll the loaf onto a lightly floured peel, seam side down. Score the loaf with a sharp razor blade or serrated knife making quick shallow cuts. Using the peel, slide the loaves onto the hearth. Quickly repeat with the next 2 loaves. Quickly spray the inner walls and floor of the oven with cold water until steam has filled the oven. Quickly close the door to trap the steam and bake 3 minutes. Spray again, closing the door quickly so that the steam doesn't escape. Bake until the loaves are a rich caramel color and the crusts are firm, 15 to 20 minutes.
To test the loaves for doneness, remove from the pans and hold them upside down. Strike the bottom firmly with your finger. If the sound is hollow, the breads are done. If not, bake 5 minutes longer. Cool completely on a wire rack.