Steam Oven Beer Bread with Marmite Butter

[Syzygies]

For outdoor use in my KK "yard oven" I stick to my sawed off skillet filled with SS chain. It works.

For my indoor oven in NYC, as it happens I bought a 2" thick aluminum disk off eBay that just fits under my round Baking Steel. This does a terrific job of evening out heat for a uniform browning on, say, buckwheat crepes. For extra steam thermal mass, I decided to store it under the chain in my cast iron skillet. It just fit, when cold. Anyone see where this is going?

I replaced the shattered cast iron skillet with this: Vollrath Company 68369 Bake/Roast Pan (I love their bowls). Won't rust, but I now need more thermal mass. One can buy scrap aluminum plate very thick in odd sizes on eBay; that's my plan when I return to NYC next fall. The rule one needs to follow here is to have enough thermal mass to make enough steam. There's no getting around the physics.

Here are my own notes from my "bread" folder:

I use a cast iron skillet filled with stainless steel chain, in both an outdoor ceramic barbecue and two indoor ovens. I add 350g to 400g water at the start of a bake, and there's a noticeable difference. I've made many dozens of loaves, and I can't imagine working without lots of steam.

Scale matters. That much water is enough is enough to displace the air in an oven several times over, so of course one observes steam escaping. The steam that remains in the oven has the desired effect.

Part of the Bouchon Bakery explanation for this technique goes: "The water prevents the crust from setting and keeps the exterior supple and cool longer..." I doubt this explanation. The 540 calories it takes to convert a gram of water to steam is released to the landing site, on any surface in the oven that's not already above the boiling point of water. That would be the bread, and with enough steam to fill the oven several times over, there is plenty of available energy to snap the surface of the loaf to the boiling point of water while keeping it wet. This delays a crust forming, while the loaf expands. Putting a loaf in a cast iron pot works for different reasons, and the results are visibly good but not identical.

I have yet to find a good resource written by a physicist that confirms this explanation, but it matches my empirical observations. While there is steam, the bread crust is pinned to 212 F and kept wet, despite the cool interior of the dough. When the steam subsides, the crust stays hot and wet; it takes a great deal of energy to convert water back to steam, so any drying is likely hot evaporation. I'd worry more about how much steam, and less about how long the steam lasts. Steam that briefly overwhelms the bread (350g to 400g, not less) quickly conditions the loaf for ideal oven spring and crust. Give me 30 seconds that looks like it should blow the door open, over eight minutes of a damp towel slowly drying. Scale matters.

Here is a review of the physics behind creating steam in a hot oven:

It takes 80 calories to thaw a gram of ice, 100 calories to bring that gram to the boiling point, and a whopping 540 calories to then turn that gram of water to steam. By weight, steel holds about 13% as much heat energy as water.

So it takes a total of 720 calories per gram of ice, or 590 calories per gram of hot water, to create steam. Each pound of preheated steel stores 454 * 0.13 calories per degree centigrade above boiling. So one computes the total calories needed for a quantity of water, and divides by the calories provided per pound of steel. For example, to convert 350g of ice to steam, one needs

(grams ice)×720÷((Fahrenheit−212)×(5÷9)×0.13×454) = 32 lbs steel at 450 F

This spreadsheet makes these calculations for other water, temperature combinations:
 

Edited June 5, 2018 by Syzygies

[Pequod]

Your hypothesis makes a lot of sense to me. It all comes down to steam, as it condenses on the dough, being a far more rapid and effective form of heat transfer to that dough than dry air, even if that air is at a higher temp. My quick (and possibly inaccurate) calculation says that water at 212F is about 200 times more thermally conductive than dry air at 400F. A quick burst of energy to the surface, followed by a longer evaporation of that moisture which keeps the crust cool (evaporative cooling) until fully evaporated. That residual steam I see venting minutes later is more likely to be that evaporating from the surface of the bread than from the pan itself.

Not a physicist, but did happen to survive a Ph.D. in Aerospace Engineering and used to work in the rocket motor industry. Fun Fact: 30% of the mass flow inside the space shuttle solid rocket motors is actually molten liquid! Imagine that impacting a dough ball (or not...).

Edited June 5, 2018 by Pequod