The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

I believe in Science

agres's picture
agres

I believe in Science

I learned the Ideal Gas Law ( https://www.khanacademy.org/science/physics/thermodynamics/temp-kinetic-theory-ideal-gas-law/a/what-is-the-ideal-gas-law ) circa 1962, and it has been on the tip of my tongue ever since.

Simply, it says that when you put bread dough in the oven, the gas bubbles in the dough expand as the gas warms. In a hot oven, with plenty of heat, this happens much too fast for yeast to do anything. The myth of yeast suddenly putting out a lot more CO2 as a result of the extra heat is an old wife’s tale.

Bread dough contains a lot of water. In the heat of the oven, water at the surface of the dough heats to over 212F, converting to steam. As water converts to steam, it expands by a factor of ~1600. Thus, the water in the crust can fill the loaf with steam, very quickly. That steam carries a lot of heat which kills yeast and bacteria, heats the gases in bubbles in the dough, and converts the hydrolyzed starches and proteins in the dough into the stable structure that we call bread.

Steam from the crust can not only carry heat into the bread, it can carry huge amounts of heat away from the baking loaf. By trapping that high energy steam around the loaf, Cloches & Dutch Ovens can be very worthwhile, particularly with gas ovens.

However, modern, energy efficient electric ovens tend to do a very good job of holding steam in the oven.

I have a Wolf electric oven. It is fabulous for a pound or 2 of yeast based breads made with white flour. I can set the oven to 375F convection mode, give it 15 minutes to heat, and bake a tray of 3 x 250 gram baguettes,  resulting in beautiful loaves, with minimal effort – no fussing with baking stones or generating steam. There is ~300 grams of water in the dough that must be heated, so throwing any additional water in the oven simply diminishes the heat available for baking the bread. (E.g., the water in the dough and the additional water must be heated.)

However, for a 750 gram whole wheat loaf, I use a higher hydration level so there is 330 grams of water in the loaf, and the oven does not really have enough thermal inertia to quickly heat that extra amount of water with a set temperature of 375F, so I set the oven to 395F.

Heat is temperature times thermal inertia. Available heat can be increased by raising the temperature or increasing thermal inertia. Available heat is what counts in baking. The higher temperature supplies extra heat to make steam of the water in the crust and bake the bread. And I still do not have to mess with steam generation or baking stones or a cloche.

If I want to bake larger loaves, I need to add a baking stone or Cloche or Dutch Oven or otherwise increase the thermal inertia of the oven.  The first step is to use a cast iron griddle (with oven set to 375F with convection) on the bottom rack. The second step is a baking stone on the bottom rack and the cast iron griddle above the baking rack. Then, both the stone and the iron griddle add thermal inertia and when hot can supply heat to vaporize water in the crust. Also, a very small loaf does not produce enough steam to fill my oven with steam, so small loaves must be baked in Cloche or Dutch Oven or my favorite turkey roaster. Or, last night I baked a very small loaf and an apple pie at the same time (convection @ 375F) and both came out perfectly. (The pie supplied extra steam for the bread.)

I like a golden-brown crust. If I want a darker crust, I can glaze it to produce a darker crust. If someone tells me to preheat my oven to more than 450F, then I presume that they have a gas oven with low thermal inertia, and which does not trap steam; and, they think readers have similar ovens. I notice that bread recipes that call for baking at temperatures over 450F also call for long bake times (resulting in darker crusts by the time the crumb is baked.) I try to have enough thermal inertia in my oven that I can bake at a lower temperature and have a much shorter bake time. Yes, I generally use convection baking, which substantially reduces baking time, but still, my baking times seem very short in the context of many bread recipes.   I expect this is true for anyone with a good electric oven.

Commercial bake ovens use steam injection because steam injection is a way to quickly increase the heat in the oven without scorching or burning the products being baked. Also, in some places steam is a very inexpensive source of heat. Adding water to (a home) oven in addition to the water in the dough cools the oven. Under some conditions it may help transfer heat from the thermal inertia of the oven to the product, but it is more likely to cool the oven and lengthen the bake time resulting in a thicker crust.  I can get a crisper crust by using a decreasing oven temperature so the last 5 minutes of the bake is at 325F.