My understanding was that the role of steam was to keep the crust of the
bread moist, which allows it to continue to expand for a longer period of
time after it has been placed in the oven. Once the crust starts to harden
your oven-spring is over, so you want to if you can slow that process down
a little if you can. To my mind, any oven hot enough to bake bread can
create enough steam to serve this purpose.
I've got a convection oven (even though I rarely use it in that mode for
bread), which means that there is a vent which allows the steam to exit the
oven. I find that 1 cup of water will take about 10 minutes to evaporate
from a jellyroll pan in the bottom of the oven. This is long enough to
allow maximum oven spring, and short enough to allow the bread to develop a
good crust after the steam is gone.
With my previous, electric convection, oven I did some tests of steam
production. What I found was that I wasn't able to get the oven over 450
degrees with the water in the bottom. My guess was that the loss of steam
out the vent (driven by the positive pressure created by the steam) was
taking heat out of the oven at a rate equal to or greater than the oven's
ability to heat it. Also, that oven had pressure pad controls for the
timer near the vent, and they would always short out due to the steam.
My new, gas, oven has a much better convection action than the old
electric. I haven't really tried to use the convection on this oven for
bread, but it would be interesting to see how various combinations of
convection (or not) and steam (or not) affect the rise and the crust of
bread. Hmmmm, this sounds like an excuse to make at least 4 loaves of
bread this weekend......
Dave Barrett