While the results are clear, I do wonder about the purported cause being keeping the outer crust soft during the initial oven rise phase. At least for home ovens at 450-500 F. Steam is not what we usually see it as a cloudy vapor. It is invisible and contains a huge amount of energy which it releases when condensing on anything. That is why steam burns are so instantaneous and severe. I do wonder if the action of steam (water vapor) isn’t to quickly impart a large amount of heat to the loaf exterior much more rapidly than either the 500 degree air or radiant heat of the oven can do alone. Convection ovens try to do this by keeping fresh hot air against the food, but while one gram of air can exchange one calorie of heat per degree, steam can exchange 540 calories / gram plus one more for the steam temperature. That steam does this without drying out the surface, it certainly will cook it fast. Remember steam radiators? They were a very efficient way to move a lot of heat around a house. It is one of the best heat transfer methods in existence.

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