Is there any benefit to adding some boiling water to a preheated dutch oven (under some parchment paper) just before putting the lid back on?
EDIT:
Well I did it. It seems to improve oven spring. Took Some pics.
And here is the crumb 
Bread – Sourdough Breadmaking: Adding Water to Dutch Oven to create more steam
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Related Solutions
Yes, you should have let the dough come to room temperature before baking. Also, you might try pre-heating the Dutch oven so that it is really hot before adding in your loaves.
I did not get an answer from America's Test Kitchen beyond that the written recipe supersedes the video, so I proceeded with the experiment. I made two identical doughs following ATK's recipe for Almost No-Knead Bread with Olives, Rosemary, and Parmesan. Knowing that I would bake them two hours apart, I even started the doughs two hours apart, so the two doughs were truly identical in every way possible. They were both allowed 18 hours for the first rise and 2 hours for the second.
For the first loaf I followed the written instructions for baking. I did not preheat the oven or the Dutch oven. When I put the loaf in, I turned the oven to 425F (219C). One half hour later I removed the lid and continued to bake until the dough registered 210F (99C), which took about another 35 minutes.
For the second loaf, I followed the instructions in the video. I preheated the oven and the Dutch oven to 500F (260C), put the ball of dough in the Dutch oven, returned it to the oven and immediately reduced the oven temperature to 425F (218C). It baked covered for one half hour, then baked uncovered until it registered 210F (99C), which took about another 25 minutes.
RESULTS
The loaf on the right was made per the instructions in the video, it used a pre-heated oven and Dutch oven. That loaf is superior in every way. As you can see in the second picture, it rose higher and the crumb is lighter. The first loaf is dense. The crust on the second loaf is perfectly crunchy. The crust on the first loaf is just hard. And, on the first loaf, the bottom burned before the bread was done.
I didn't think starting the bread in a cold Dutch oven made any sense, this experiment clinches it for me. If you're going to bake bread in a Dutch oven, I recommend that you pre-heat it.
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Best Answer
What you are doing essentially allows the bread to rise a little more before the crust toughens. It will leave you with a lighter, fluffier loaf with smaller air pockets and a softer crust. I have never poured water into the dutch oven before, but I often just wet the loaf right before putting it in. You can do that with a spray bottle or basting brush.
I'm not sure how exactly your method will differ in results though, as it will do 2 things: rapidly lower the temperature of the dutch oven (transferring the heat to the water) and start cooking the top of the loaf faster.