steam is *not* always the same temperature
I've been reading through the forum archives and have come across several threads where steaming methods were discussed, and the statement has been made that "steam at atmospheric pressure is always at the same temperature", and I haven't seen anyone refute this. As understanding steam is important for crusts, I thought it was important to set the record straight on this, and rather than resurrect old threads, I thought it'd be worth starting a new discussion.
In short, it's not true.
Steam is the gaseous phase of water. Liquid water at atmospheric pressure can never go above 100C/212F, because at that temperature it starts to change phase, and all energy put into it is swallowed up in the power-hungry process of phase change. But once the water is fully converted to steam, it can get hotter, and it does - this is called 'superheating'.
Why this is important is in the difference between a pan of water in your oven and the 'live steam' I believe bakeries use, which is injected from a pressurized boiler. Our pans of water at home are producing a mixture of steam and vapour, not pure steam. Vapour can't top 100C, and the steam produced by this process won't be much over it, either. But steam injected from a boiler will be pure steam, no vapour, and is likely superheated. So its effect on the crust will be that much more dramatic.
I hope this helps.
Source:engineering degree
... but thermo was over 25 years ago and I've forgotten 98% of my knowledge of steam. I do recall saturated steam, dry steam, and superheated steam ... a quick review at wikipedia didn't help. I would speculate, however, that a container of water in my oven isn't going to give me anything more than saturated steam (since I cannot seal the oven and create a higher pressure system).
Now an interesting question to ponder ... what is the 'best' type of steam for baking?
Cheers-
Dave
That we didn't study modern thermodynamics, that subject was limited to how to start a fire with a piece of flint But if I remember correctly, superheated steam acts like an insulator, not giving up a lot of energy until its cooled to the saturated steam phase, so I wonder if this is good for bread so as to not give heat, but to just keep the bread wet. However I then think that to actually wet the bread (to keep the crust from forming) that the temperature of the steam has to be low enough to allow the water to condense, which would be the definition of saturated steam.
To be honest, I have blocked out a lot of Thermodynamics as a traumatic experience, but some of it stuck.
It's an interesting question, and not one I had really pondered until earlier today, when reading an old thread about a bakery that had apparently used pressurised steam. I tend to assume "hotter is better" but you make a good point - surely the main point of steam in baking is to transfer moisture to the dough, or at least prevent it from drying out to let it have good oven spring. You do need some condensation too, don't you, to help caramelisation? Something about gelling starches comes to mind.
Certainly an insulating effect doesn't sound like a great idea. When you steam things on the hob they cook rather faster than the same things cooked in an oven, which I believe is down to the steam and vapour having greater heat capacity and conductivity than the dry air in an oven, even though the oven air is at a higher temperature. So perhaps steam in bread baking also has a role in increasing heat transfer. Perhaps if you go mad superheating it you ruin that effect.
There's only one experiment to test this ragbag of hypotheses: somebody get hold of a steam locomotive and we can convert it into a bread oven. We can try baking test loaves in the firebox, steam dome and funnel and compare results.
that I happen to know a man who formed group to buy and restore a steam locomotive, he's the chief scientist that trained me many years ago so I'm not sure that he is still with but if he is, then he would certainly allow me to use his locomotive to run this experiment (as long as i supplied the fuel, of course). I'll let you know what he says.
I live 10 minutes walk from a small preserved railway with many steam trains, however they're all turned off right now for maintenance...
Converting one into a bread oven... Tricky ... :-)
I'll suggest something to them, however I suspect they'll all die laughing... However I've just spent some money with them in the engineering workshop for something I may post about in a weeks time, so who knows...
Anyway...
The firebox - burning anthracite and running at a about a million degrees C... A quick bake with a well defined if somewhat blackened crust...
The steam dome - a fairly hot and dry environment under pressure (assuming non-condensing superheated steam), however the addition of a relatively cool lump of dough ought to produce condensation - for at least a short while. The down-side is the pressure which I fear would crush the bubbles in the dough resulting is a somewhat flattish bread with an interesting texture. Assuming it doesn't explode into a million pieces when you release the pressure to get the loaf out...
The funnel - very short funnels on UK trains, however with the steam injectors going into it to increase draft through the firebox, then... Possibly a good environment if it weren't for the soot and other by-products of burning anthracite...
I have seen breakfast cooked on a shovel poked into the firebox though - as in sausage, bacon and egg. Slap some dough onto a shovel, cover it with a cloche/dome and poke it in and you might end up with something edible - if you can withstand the heat for long enough and the shovel doesn't melt or the wooden handle burn... My little office fire can easily exceed 500C when I burn anthracite in it.... (500C is the max. my IR thermometer goes up to)
Oven steam injectors do seem to vary - the one I have is simply a solenoid valve (push button on the front panel) that sprays cold water into the baffle plate at the back of the oven - the fans then carry this into the oven. More than 10 seconds of "steam" and the back plate runs out of heat and I get a puddle at the bottom (which is no worse that throwing a cup of water into the tray at the bottom of my other oven as it soon boils off)
-Gordon
we could slip a couple of loaves in there and see what we can make out of them.
Such as:
Crispy Anthracite Blacked Brioche to go with blacked fish
Steam Crushed Flatbead for a global wrap
SootSational Sourdough
What about pizza? I bet you could cook a good pizza on a shovel in a firebox. Just preheat the shovel first.
I have a cast iron multifuel heating stove, and I have often considered making pizza in it - I reckon I'd just need a steel frying pan with a nice long handle. Leave it in for a while to preheat, then pull it out, stick in the pizza and back in the oven til it's done. That thing gets screaming hot, way hotter than my oven.
Well, like you, I have a multi fuel stove (in my office)...
http://unicorn.drogon.net/officeFire.jpg
its burning wood there, but burns coal just fine - inside temperature is hotter than my IR themometer which I think tops at about 500C... However it's not very big.
We have a bigger one which is wood only in another room, so there is a possibility :-)
I have some steel to collect from the local preserved steam kettles on wheels later this week - I will ask them when they're next setting fire to them, so who knows...
Cheers,
-Gordon
That's pretty similar to mine. I generally burn smokeless ovals (the compressed coal briquette things) and they burn very, very hot indeed, much hotter than wood. I once overloaded it and the cast iron started glowing cherry red... oops.
Is there such a thing as too hot for pizza?
edit to add, it never occurred to me at the time, but when it was glowing I could have slapped dough on it and made naan. So many unexplored possibilities.
Has arrived...
http://www.thefreshloaf.com/node/41508/anthracite-special-platform-9%C2%BE
Enjoy ;-)
-Gordon
I like your proposed experiment!
-Dave
Acutally you're right. A boiling pan of water will only "cool" the oven - the water changing phase to steam will maintain a temperature of 100 dC / 212 dF. Sort of a fatal "whoops" when it comes to the idea of high heat for maximum oven spring. This is why bread baked in cast iron dutch ovens works so well.
I switched to using an inverted Stainless Steel Steam Tray pan sprayed with Pam to keep it from sticking to the loaf. The cloche is sprayed with a couple of squirts from a water sprayer before being placed over the bread.
Aluminum foil roasting pans can be used for the same purpose.
Wild-Yeast