I have been having difficulty overproofing my baguettes, so today I tried an experiment. I shaped three similar, though not quite identical, baguettes then baked them one after another, 27 minutes apart. You can see the results here, with the last bake on the left and the first on the right.
The first baguette went in the oven at just at the point where it had nicely filled out in the couche (smoothing out the little wrinkles that occurred during shaping) and an indention made with a fingernail would fill in slowly. It has good oven spring but the slashes didn’t open as much as the next two. I worried about the second loaf because it had gone a little flat but it actually has the best oven spring and expanded slashes of the three. The third is still pretty good but it’s starting to sag just a little. So, my conclusion is that I’m going to start my oven at about that fingernail-test point from now on and when it is ready 20 minutes later, my dough will be ready too.
I did an accidental secondary experiment because the second baguette got less steam than the other two. I have a cast iron skillet with a few objects in it and I pour water in there just after I load the bread then quickly shut the oven door. If I do this right I will get clouds of steam leaking out through the oven door and the vents on top of the stove. That didn’t happen with the second baguette for whatever reason. It doesn’t have the same golden brown crust (I know it's hard to see this in the photo, but it's true) as the others though it’s still got the crunch and tiny blisters we crave.
A few details: My formula was 60 g of 60% starter made with bread flour; 500 g King Arthur APF; 360 g water; about 15 g salt. I autolyzed, did a few stretch and folds and allowed the dough to develop in a 60 degree room for about 5 hours then it went into a 39 degree refrigerator overnight. I preshaped right out of the refrigerator, rested and let it come to temperature for 75 minutes, shaped and proofed en couche for 75 minutes at 68 degrees. Starting oven temperature was 500 degrees; I turned it down to 480 degrees after loading the loaves. Bake time 27 minutes with a turn at 10 minutes; I don't remove the steaming apparatus because the water just evaporates away.