Commercial bread baking ovens are equipped with valves that fire bursts of steam to get the job done, but conventional ovens need to be gamed to make sure that there is adequate humidity. I'm sure that I have tried more ways to get water into my ovens for baking than I can recall. But I'll give it a go; over the last 3 decades I have
- Sprayed the walls of the oven with a spray bottle
- Soaked rags in water and put them in a bread pan in the back of the oven
- Rigged the milk steamer from an espresso machine
- Put a pan, a skillet in the bottom of the oven with ice cubes
- Placed a sheet ban with water in the bottom of the oven
- Soaked bricks and placed them on the oven floor
The photograph directly below shows how I set up my oven to bake hearth bread following Reinhart's technique.
A sheet pan is placed on a rack that is as high up in the oven as it can go. The oven is then preheated to 550 degrees Fahrenheit. When the oven reaches the preset temperature I slide the dough in from a bread peel, pour 6 ounces of hot water into the sheetpan, slam the door shut and bolt away to avoid getting a steam burn.
After about 8 minutes I drop the temperature to 450 degrees -because by that time oven spring is finished and there's no point in keeping the oven cranked- and let the bread "bake out."
Okay, so why put the pan of water in the top ot the oven and not at the bottom where the heating element or, if you have a gas oven, flame is? Well, the answer turns out to be pretty simple. Heat rises, so as long as you have good seals on your oven doors, the ceiling of the oven will usually be hotter than the floor. I've proven this many times to myself and my students by shooting the oven with my surface reading thermometer (seen in the photo below and here).
Note: Temps are for ceiling and floor of oven. I did not heat the oven to full bake temp. to conserve energy.
Putting the water at the top also gives a more forceful production of steam because when the steam that is generated in the pan hits the top of the oven it gets super-heated and then forced down towards the bread by the oven roof and walls.