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Many many years ago I stumbled across Chad Robertson’s first book Tartine. It was eye opening in many ways and in 2013 I spent time in San Francisco as an excuse to go to the Tartine bakery.
One of the things that every home baker knows about is the importance of steam when you are baking bread. What does steam do?
On Food and Cooking: The Science and Lore of the Kitchen by Harold McGee is pretty much the science-of-cooking bible. McGee writes that steam does the following. It increases the rate of heat transfer from oven to dough (by as much as 400%) and causes a rapid expansion of the gas cells in the bread. The steam condenses on the surface of the dough, and creates a film of water that stops a crust forming. This helps to keep the surface of the bread elastic which means the dough can expand — what is known as the oven spring. The hot water film then “gelates starch” on the loaf surface into a thin covering which later dries into a shiny crust.
Yay steam.
Robertson’s book was the first time I’d read of using a dutch oven (Robertson recommends the Lodge combo cooker) inside the oven as a way to aid oven spring. It works by creating a sealed environment for the bread and as the bread heats up it creates a steamy environment for itself. That’s right, it steams itself. About half-way through the baking you take the lid off and finish the baking once that starch has been gelated.
The quality of my sourdough bread was transformed immediately: better oven spring, lighter crumb, richer crusts.
Yay steam.
By the way, modern domestic ovens aren’t ideal for this process. Gas ovens are actually vented to allow carbon dioxide and water to escape and therefore don’t retain the steam of loaves. Electric ovens do a better job and most readers will know of putting some ice or water in a tray at the bottom of the oven to add steam.
