I used BBA (Peter Reinhart) French Bread formula (page 170) for these but I made an adjustment by using 50% rye flour in the pate fermentee and by using 100% AP flour in the final mix instead of a 50/50 mix of AP and bread flour.  I also changed my procedure by leaving the loaves inside the open oven, with the oven rack slid only about half way into the oven, for the first fifteen minutes of cooling.  Result was a slightly sour flavor; just enough to let us know it was there, a light crunch to the crust and a temptingly chewy texture.