Thermodynamically there is a huge difference between injecting steam
into the oven and injecting water. This difference can be summed up in a
single physical law; heat of vaporization. Heating water to 212 degrees
is in and of itself not enough to boil water and create steam.
Additional heat must be put into the water at 212 degrees to make the
conversion to the gas phase. Because of the tight bonds between
molecules in liquid water, the heat of vaporization is very high. It
takes five times more energy to convert water at 212 degrees to steam at
the same temperature, as it does to heat the same amount of water from
32 degrees to 212 degrees. (
http://en.wikipedia.org/wiki/Standard_enthalpy_change_of_vaporization
)
What does this mean in practice? There are two reasons that injecting
water is nowhere near as effective as injecting steam. The first has to
do with timing. Timing of the injection of steam is critical. Injecting
steam into the oven must be done at the very start of baking. Even a
delay of a few minutes changes the effect. When you inject water versus
steam there is a time lag in converting the water into steam.
(http://www.kingarthurflour.com/stuff/contentmgr/files/15ec5c94af1251cdac2d7a25848f0e27/miscdocs/water.pdf)
The second issue has to do with concentration of steam required to
create the desired effect. Introducing liquid water into the oven will
never generate the concentration of steam that is optimal.
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