Hi Everyone,
We finished the final photography yesterday and it really has me re-energized! I love the shots we got. Photographer Ron Manville and Ten Speed's art director Nancy Austin set up a photo studio in one of the Johnson & Wales bakeshops while I baked the breads in the bakeshop next to it (the students were on their trimester break so we had the bakeshops all to ourselves for a whole week--thank you J&W--it would have been impossible to accomplish this without that resource!!!). I'm taking the weekend off to recoup from the effort--I'm just getting too old for this, but when the book comes out I'll probably forget about how tired I've felt for the past two years.
I just got an interesting e-mail from home baker Jake Sterling with some thoughts and theories on why steam helps hearth breads. I'm attaching part of his letter for general information. Write to me at [email protected] if you'd like me to pass on any responses to Jake (eventually, when I figure out how to do it, I'll put a response mechanism directly on this blog).
Enjoy! More from me soon, but here's Jake....
Dear Peter,
What I am writing about is a statement you make somewhere in Crust and Crumb about the temperature of steam in the oven.
You say something like: "Of course the temperature of the steam can't get above 212 degrees Farenheit."
Actually, that's not right. Water can't get above 212 degrees because at that temperature it turns to steam. (212 is the temperature water boils at sea level. Water can be boiled at higher temperatures if it is under pressure, as in a pressure cooker.) But steam itself, just like air, can get much hotter.
The physics of this are pretty fascinating and must have a lot to do with the reason a steamy oven is so much better for bread baking. Basically, heating water doesn't take that much energy (heat) but when it gets to the point of turning into steam there is something called a phase-change that occurs. The tiny temperature change that causes the transition to steam requires a whole lot more energy to accomplish than a similar temperature change that is merely heating the water. This is why, when you boil a kettle of water, it doesn't just suddenly all turn to steam when it gets up to 212 degrees. Every bubble of steam that rises takes so much energy that the rest of the water is starved of additional heat and remains at 212. But once the water has turned to steam it can be heated even hotter. For instance, H2O released from burning is generally much hotter. So, I think the steam in the oven, especially a brick oven, would, like the general oven atmosphere, be much hotter than 212.
That's not the end of the story, though and here is where it gets really interesting though I don't know know for sure what the effect of this is on bread. At the transition point when steam condenses back into water, it suddenly releases all that extra energy in the form of heat. This is why, in a sauna, if you throw some water on the hot stones, the temperature in the sauna feels as if it had just jumped way up even though a thermometer would tell you that it was the same temperature in there. What is happening is that the steam that was produced from throwing water on the hot stones is condensing on your (cooler) body and releasing it's heat. Your sensations are not wrong -- your skin is receiving more heat, but the actual temperature of the sauna atmosphere has not changed appreciably. This also happens when water condenses on your windows on a chilly day. Lots of heat is lost from your house through that process.
My hypothesis is that the same thing happens when you put bread into a steamy oven. In the first few minutes, while the surface of the bread is still much cooler than the temperature of the oven, steam condenses on the surface of the bread and there is an immediate and intense transfer of heat to the bread over and above that which occurs from conduction, radiation, etc.; and this cooks the crust but, at the same time, doesn't dry it out; and this is what is responsible for the improvement in oven spring and the final taste and texture of the crust.
If you think about how intensely the apparent temperature in the sauna changes with the addition of steam, you can imagine how much more heat is being delivered to the bread when the steam is heated to bread oven temperatures!
Take care
Jake Sterling