Ok, I'll play along. ;) The moist, hot environment improves oven spring by transferring heat more rapidly to the dough (moist air is more thermally conductive than dry air), keeping the dough surface from drying out and getting stiff. It improves crust quality by gelatinizing the starches on the surface of the dough, causing them to brown better, and form a more distinct "crust", rather than just a skin of browner bread.
To get more steam in your oven, in addition to the simple methods you noted, spritzing and pans of hot water, you can:
- Bake inside a vessel like a dutch oven preheated in the oven. Gives both thermal mass for browning, and traps naturally produced steam around the bread. Remove the lid for the last 10 minutes of baking.
- Cover the baking bread with a large bowl or pan for the first 10-15 minutes of the bake to trap naturally released steam.
- Use one of several commercial steam injection kits (most look like a steam cleaner that allows you to blast some steam manually into the oven when loading).
- Build your own steam injector, like this handy baker. The gist is that they use a pressure cooker with a flexible metal hose attached to an output port and directed into the oven. Boiling water in the pressure cooker produces steam. Pre-steaming the oven for 10 minutes before baking and for the first portion of the bake produces impressive results.
In addition to getting more steam in, you can improve the crust and oven spring by using delayed or cold fermentation, which creates more sugars (better browning), and more extensible dough (better oven spring).
Without seeing the loaves or knowing your exact procedures, it's hard to guess. My money would be on too dry a dough. Could also be inactive starter, too long a bake, not a hot enough bake, not enough rise time/temperature. So I'll just talk about how I make sourdough in the hopes it'll help. These are techniques I've learned from various books (most notably Reinhart's The Bread Baker's Apprentice) and experiences.
If I did it right, you can click any of the thumbnails for full size images.
First order of business, of course, is having a nice, active starter. I build my final starter from the barm the day before. Depending on my schedule, I either leave it at room temp all night or feed it earlier in the day and pop it in the fridge. It then comes out to warm up a few hours before I bake. It should show strong signs of life. This starter was made with nothing but flour and water--no grapes, no commercial yeast, no juice.
Then comes mixing and kneading. I like to mix the starter with the water first, allowing the starter to break up and dissolve a bit. This ensures good mixing with the final dough. Then I add the flour and salt, mix to a coarse ball...
...and switch to the dough hook for 5 minutes or so. The dough should be stickier than you think it should be. Turn it out onto a floured surface for 4-5 minutes of final kneading by hand to adjust the flour. It should be smooth and supple, still be a bit tacky, and pass the windowpane test. When you stretch it to form a boule, the outside should be smooth and not tear.
Let it rise 3-4 hours at room temp or slightly warmer (a closed oven with a bowl of hot water works well). Then shape and proof for another 3-4 hours.
I start with a very hot oven. 500-550F for artisan loaves. If using a stone, get it in there 45-60 minutes before baking, that way the stone and oven get a good heat soak. Then when the loaves go in, you want to create steam to allow the bread to rise before the crust hardens. A steam pan is a good idea, and I also spray down the walls of the oven with a squirt bottle. Be careful of squirting the light bulb--it will shatter. Don't ask me how I know. After a few squirts, turn the heat down to your final baking temp. I usually go with 450F.
Don't forget to slash them, too. That helps them expand and prevents blowouts. I had some issues getting these guys onto the stone (not my finest hour), but they were still outstanding. You can see the crumb is open and light, but still gelatinized and chewy. Perfect, in my book.
Best Answer
I've since figured it out. Gluten free bread is very particular, and the moisture has to be just right. If there's not enough water, the dough is too dense and won't rise. If there's too much water, it will rise, but in the oven, the bubbles bubble through the too, causing the loaf to collapse (I sat and stared and watched it happen). I've since learned what the dough must look like. It looks like thick cake batter. Should be smooth looking, but not soupy.