July 23, 2009 - 1:36pm
Is it worth the energy to heat up a baking stone for an hour?
I was telling a friend of mine about Eric's observations (now, mine too) about how much heat baking stones lose as soon as you put dough on them. She remarked:
I think thermal conductivity may come into play. Some materials transfer heat more easily than others -- You can put your hand into a 500˚ oven without much pain, but if you touch a 500˚ pizza stone, you'll burn yourself, because stone conducts heat differently than does air. So although the stone may lose heat, perhaps (and I'm just guessing) it transfers its remaining heat faster than would a baking sheet, etc.
What do you think? Is it worth it to use a baking stone or not? Does a baking stone transfer heat faster than a baking sheet?
--Pamela
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Your friend is wrong. Thermal conductivity of steel is 20-40 times larger than that of brick and thermal conductivity of aluminum is even larger - 250 times. But it is not only about heat conductivity, it is also about heat capacity, and the ability of thermal mass to accumulate heat, and since baking stone is typically much heavier than baking sheet it can store much more energy.
So tell me more, please. Are you saying that I shouldn't be concerned that might baking stone which I heated up for an hour at 500º lost almost 100º after putting a little piece of pita dough on it?
--Pamela
How did you measure that?
I measured it with an IR thermometer. I measured the stone before putting the piece of pita dough on it and then I measured the stone where the pita had been when I removed it about 2 minutes later. I preheated the oven for about an hour.
--Pamela
You may loose 100º of your oven temperature opening the door, but I'd bet that you don't loose 100º of your baking stone temperature. You need to get an IR thermometer to check it out.
Can an IR thermometer read the mean temperature of the stone? I think it can only measure the temperature at the surface of the stone, which is not the whole picture. I suppose the surface of the stone can heat up quicker than the internal temperature.
I think the ability of the stone to retain heat is not the only property that is of value. The fact that it is very able to conduct heat can transfer heat to the dough, but it can also transfer the heat *away* from it, too.
That explains why the bottoms of my breads (especially the sweet, oil-enriched ones) take a lot longer to burn when I cook them on a stone in comparison to cooking them on a sheet pan. I reckon the sheet pan can conduct the heat from the air (convection) and the direct heat from the element (radiation) very efficiently to the dough, which causes its bottom to burn.
=== Can an IR thermometer read the mean temperature of the stone? I think it can only measure the temperature at the surface of the stone, which is not the whole picture. I suppose the surface of the stone can heat up quicker than the internal temperature. ===
You are correct: the IR thermometer is measuring the infrared waves emitted from the surface of the stone. Clearly these bear _some_ relationship to the overall energy content of that stone, but on the other hand you could turn on the broiler for 3 minutes and get a much higher surface temperature that wouldn't be the average temperature or indicative of the energy content.
People who are interested in the temperature of their brick ovens drill holes at various depths in the refractory and insulating material and cement thermocouples into them to get the temp at various depths into the energy-storing components of the oven.
sPh
Note the word "emit" above; hence the term "coefficient of emissivity" you might find in the instruction manual for your IR thermo. The first IR thermometers had a dial to set the emissivity of the target so that the measurement would be correct. Low-end household IR thermos are usually set for the average emissivity of typical household materials (around 0.95 IIRC). If yours does not have a setting for emissivity of the target you might have to apply an adjustment factor (available from the manufacturer) when shooting your stones.
You can take out heat from the oven that you put in. This saying is used a lot when firing up a wfo for baking. Meaning the longer your fire your oven the longer you are going to be able to bake in it.. This how a wfo oven works. So I would think a stone in your home oven would work the same. Your IRT is only going to measure the outside temperature. With a wfo oven the floor, roof, sides all have different temperatures in the beginning..so the oven needs time to let the heat balance out before baking. The floor will cool where a pizza has been cooking..but retained heat will bring the floor back to the hotter temperature. So I would think the same would be for your oven stone. I pre-heat one hour when baking with my stone or stoneware/la cloche. This way I can make several pizzas indoors on my oven stone by only waiting a few minutes or putting the pizza's in a little different spot each time..I have two large stones that cover the complete shelf.
Here is a picture of thermal mass in a pizza oven http://www.fornobravo.com/pizza_oven_selection/thermal_mass.html hope this link works..
Sylvia
That's a good chart and site with a lot of information about thermal mass. Thanks for posting the link to it. It is helpful.
This is turning out to be a good discussion from my point of view. I can also now see why people like those Hearthkits.
--Pamela
Every bit of energy that is not used to actually bake the loaf is--wasted. All the btu's used to heat the oven and all the btu's remaining after the bread is done. And if you are running the AC to combat the heating of the house in the summer, that also is wasted energy.
You can argue that the crust is crisper, the crumb is softer or any other property of the bread. You can't say it's necessary for baking. In the case of a WFO, folks try to use all of the residual heat for other tasks. I suspect that comes from knowing how hard it is to gather fuel.
Some electric ovens power the top elements during the baking cycle. This in effect creates the same heat ratios found in a earthen oven.
Eric
...of which I am *definitely* one.
I've also pondered the question posed by xaipete
Many bakers here use baking stones and most reputable books on artisan bread uniformly recommend them. However, preheating instructions (initial heat setting, length of time to preheat) are all over the map.
Some bakers here, both those who use baking stones (and those who do not) are concerned about energy costs. We want to get good performance from the baking stone we've bought, but not spend unnecessary $$$ for a lengthy preheat.
I'd really like to hear from experienced, practical home bakers who make artisan breads about the *lowest* temp and preheating times they've found effective for a "lean" (primarily flour, water, salt, yeast) boule or batard with an approximate pre-baking weight of 1-1/2 pounds, containing no more than 20% whole grain and with a hydration of no more than 80%. I'm not trying to be picky by stating the above forumula but I think this establishes the parameters of what many here make as their daily bread.
I'm looking for a good oven spring, good grigne and a thin crackly crust. I don't want the dough to spread out - I want it to spring *up*. Can you help me? In order to help me, do you need more information?
Maybe the question ought to be: Who doesn't preheat at 500º for one hour?
That's what I've been doing and I get good results.
--Pamela
Much depends on the size of the stone. The thicker the stone, the longer it should be heated. I use half-inch tiles, and from experience I know that heating them longer than 30-35 minutes does not help. With thicker stone an hour would be a reasonable time. As to the temperature, the advice I heard is to heat to your baking temperature +50F.
On the other hand, things you're looking for depend not only on how long was the stone heated, but also on the shaping, correct proof, and slashing technique.
Hi Pamela,
You might try your pita bread IR reading experiment at 30 minutes preheat, 1 hour, 1 1/2 hour, 2 hours. Does it change? Then you can try finding out how fast the surface temperature recovers at various preheat times as well. Oh yeah, and maybe bake some bread :-) I'm very interested in these experiments myself. Tomorrow I'm picking up a new stone, and the IR thermometer, and a pair of Kevlar gloves among other things from a shipping/receiving depot in the States.
:-Paul
You if want to save the most energy then maybe it's better to just do all the baking you can in one day?
That's why they had communal ovens.
Good point but what would I do the rest of the week?
--Pamela
Even though I do religously preheat my stone in the oven, I take a broader view of its used in baking my bread. The heat from the stone helps brown the bottom of the loaf, but that's really secondary to my greater interest in using it for break baking. I can brown the bottom of my bread loaves using a sheet pan, but it doesn't "hold onto" heat the way the stone does. So the stone's primary purpose in my oven is to help maintain a more constant temperature throughout the baking cycle.
I recognize that, in the mind and experience of the professional baker, I may have it backwards. If that's the case I'm eager to learn where I made the wrong turn. But in my VERY limited experience, that's the conclusion I've drawn.
I don't. I preheat the oven to the temp stated in whatever recipe I'm using (generally 460F). My oven has a preheat function and beeps when the designated temp has been (allegedly) reached. I use two oven thermometers, so I go by those. It takes around 30-35 minutes to reach 460F (I have a newer, very well insulated, natural gas stove).
My baking stone lives in my oven. It heats up with the oven, but is really there for the ride until it receives the bread. I see it more as a tool to use in baking my bread rather than a factor in determining when I load the bread. I really don't care what the stone's exact temperature is, so long as it is hot (which it is). The bottoms of my loaves are always nicely browned - never burned - and I like the results I get with the stone much better than the results I was getting with a metal baking sheet.
My stone resides in my oven also. I preheat to 500 and my oven functions as Lindy's with the indicator beep. My oven doesn't take much more than 20 minutes to reach that temp.
I just baked this bread this weekend. Not a stellar loaf, but you can see the crust. Well browned, top and bottom. My picture taking leaves something to desire. It isn't burnt.
Betty
Subject 3 is Betty who preheats to 500º but loads her loaves when the oven beeps after 20 minutes. I'm not really sure if Betty's oven is really at 500º (I doubt it), but for what ever it is worth.
--Pamela
I have been fortunate to have fairly decent results. I've provided some pictures, showing what I've baked.
Thanks, Lindy. So in our survey we have one person who only heats to 460º for 30-35 minutes.
--Pamela
That's correct only as it applies to a particular formula I'm baking. If a 500F oven is called for, I'll preheat to 500F. The magic number is what the recipe says the bread should be baked at.
All my bread books advocate baking on a stone, but not a single recipe says "preheat the oven until your baking stone reaches XXX degrees F/C."
My parents advocated waste not, want not. That's a good philosophy to follow.
But don't many of the recipes say to preheat the stone for an hour? When you preheat to 500º, do you load the loaf as soon as the oven beeps?
--Pamela
Gee, Pamela, I don't recall any bread recipe I've baked stating that the baking stone should be preheated for an hour. I'll check again when I get home tonight, but offhand, I don't think I've ever seen that suggested....except at TFL.
When I preheat to any temp, the preheat beeper may go off but I don't load the oven until the oven thermometers confirm the required temp has been reached.
Maybe I'm missing something, but if the oven is at the desired temp when the bread is loaded to the stone, the stone is hot. The bread gets good oven spring and a nice bold crust, top and bottom.
What's the alleged advantage of preheating the stone for an hour?
I'm pretty sure PR's books tell you to preheat for an hour and there are others too. Did you read Dan's post below?
http://www.thefreshloaf.com/node/12995/it-worth-energy-heat-baking-stone-hour#comment-77409
--Pamela
The oven is probably just measuring the outside temperature of the stone and not the inside..thermal mass of the stone...we have been having a lot of fun measuring heat with out new instant read IRT and thats what they do..something can be 450 on the surface but not internally! There probably is enough heat retained to do a loaf..and then when removed letting the oven heat up a longer giving the stone time to recover works for the next load! If I do several pizza's in my oven..it reguire's full temp..550 and pre-heat time of at least 45 minutes..or the stone cooks each pizza taking a little longer...they take the heat right out of the stone fast! I like my pizza's to cook fast and hot..only taking a few minutes. I even notice this in my WFO when it's heated up to over 700F if I set a pizza in the same spot..it takes recovery time for that heat to come up from the interior of the floor that was put there by a longer firing of the oven..I can see not only on the crust but the time it takes it to brown..you only get the heat out that has been put in..meaning longer firing time to get that accumulated thermal mass.
Sylvia
I'm right with LindyD. I don't preheat to 500 dF and I load my first loaf within a couple of minutes of the beep indicating temp (450 dF) reached. The bottom of my loaves look just like the tops and sides in color. Oven spring is enough to create ears and bloom. The second loaf does the same, in spite of the more comprehensive pre-heating it receives. And BTW I have a 3/4 inch thick stone.
The bread results I get are much better with the stone. I can't measure the energy used with stone and without, but my gas bills are the same either way, and I guess that's as good a guide as any.
David
I am right there with Lindy also. My stone also lives in the oven and when the oven is preheated then the stone is preheated as well. It may not be at the same temp as the oven right away, but it is nearing it on the inside. It's not like placing a cold stone in a hot oven, and preheating the stone that way, the stone heats with the oven.
14"x16"x5/8" from cooking.com.
I love this site. Where else can you get an in-depth scientific discussion about thermal transfer in the same thread as the history of pre-industrial communal ovens? And even some practical advice thrown in for good measure!
I compromise and preheat for 30 minutes after the oven reaches temperature, before putting the bread in. I preheat only to the temp. required by the bread, not to 500 degrees.
I have to use an oven thermometer, as opposed to depending on the oven controls and my general feeling is that when the controls says it is up to 460 degrees, for example, the stone really is not. Thus, the extra 30 minutes or so.
I think there are so many variables with regard to ovens that each of us has to do what works for us.
I keep saying that I need to get this oven fixed, but getting the company's repairman out here to the boonies is such a hassle that I put it off. So far we are making it, though I have to pay much more attention that previously. Maybe that's a good thing!
I haven't baked anything from the BBA for some months, but I do think PR may have advised to preheat the stone for an hour when baking the ancienne baguettes. I just don't recall whether I followed that advice. Will have to wait until I get home to see if I can find any texts which mention an hour preheat time for a stone.
I read Dan's post, but I get good oven kick and more than adequate browning of the loaf bottom without a 60-90 minute preheating of the stone. So why waste natural gas (and money) for such a long preheat?
Like Soundman, I see no difference in the result when doing consecutive bakes, where the stone has the benefit of being continually heated in the oven during the preceding bake.
To take the topic to the other end of the spectrum, I recall rearding earlier posts about how wonderful bread came out of the oven with no preheating and a cold stone. I never had the courage to try that.
For those who live where it's HOT (I'm in S.CA) and want to save energy, how about setting the stone out in the sun for an hour or so, loading it the oven and then preheating for a shorter time? I make this suggestion partly in jest, but hey - it might work!
This has been a great thread! Thanks Pamela.
Marni
If I lugged my stone out into the sun and was lucky enough not to break it, my little dachshund would no doubt stretch his tiny body out on it. I've never seen a dog that liked heat as much as my little hot dog.
--Pamela
My little dog loves to sun himself on the granite flagstones, wearing a fur coat no less! Go figure.
David
In Las Vegas you could actually fry an egg on the stone...though in Vegas they use the word..sidewalk! Glad I live in S.CA now..it's hot but not as hot as Vegas! There you could put a solar oven to great use!
Sylvia
I wonder if that makes any difference in the amount of time it takes to preheat an oven and/or stone.
Electric, Lindy.
--Pamela
Maybe that's the biggest variable here, gas or electric. My oven uses NG.
David
What the stone does is temper the oven and speed the heating of the dough. This is going to be long so be warned!
I have a wood fired oven that I heat for about 2 1/2 hours with a big fire to heat load the oven. When I remove the ashes and coals and lightly mop it the temperature of the hearth cools to about 650 F. The dome will be around 950. I then close it up for an hour and let everything stabilize and the temp of the surface of both the dome and the hearth will be around 550 (yes the dome is slightly hotter).
I load the bread (about 15-18 pounds) at about 550 and spritz the interior with water. This will cool the surface of hearth and dome significantly (I haven't checked the temp but under the loaves is probably 400 or so, maybe less. The air in the oven will be pretty cool - probably 250 or so. But the heat deeper in the walls and hearth flow back to reheat the air and bake the bread. 50 minutes or so later when I remove the bread the hearth and dome temp will be around 475. (It will be hotter if I burn longer before I begin the bread - but I ususally only do one batch.)
The stone in your oven does the same thing - but not as well for it is very light compared to a WFO, but it helps reheat the air and gradually (think gracefully) raises the temperature at the bottom of the loaf as heat seeps back to the oven.
When you put a loaf in an oven on a cold metal pan where does the heat come from that warms the pan and the bread? From the air only and most of that heat comes from the heating element (or flame). What do you think the temperature is in an oven when you first begin baking? Close to 212 (due to the steam you release from your steam system). And don't forget a lot of the hot air in the oven BEFORE you put the dough in left while you loaded the oven. So, finally, which oven should get hot faster - one that is a naked oven or the exact same oven with a stone preheated to baking temperature. The answer is obvious!
If the goal was to heat the bread as fast as possible we would bake on thick sheets of preheated steel. But you would burn the heck out of the bottom of the bread for the heat would rush to the bottom of the loaf (good conductivity!) and it would be a disaster. The heating rate is important! You want it slow enough (and with enough humidity) to let the crust gelatinize and the gases and some of the alcohols in the loaf to come out of solution (vaporize) and expand to lift the loaf. Too fast and the crust will set too fast and the results will suffer. Too slow and gases will escape excessively and the results will suffer. That is why these "standards" have been arrived at - they have the right "heat profile' characteristics to give a good loaf.
Short cycling a stone (i.e. not heating it through and unless it is REALLY THIN 20 minutes is NOT enough) simply means the stone won't temper the oven as much and the rate of temperature recovery will be slower. Not a disaster. but it probably means you will get better loaf volume and oven spring if you heat the stone longer. Having your oven say the oven is at temp only means the air reached that temp. Yes it takes a bit longer than if there were NO stone in the oven but not a lot. But at that point the center of the stone is still pretty cool. I have a Hearthkit stone for my indoor kitchen and it has a thermometer slot that allows one to get the temp (sort of) IN the center of the stone. The Hearthkit is really thick - about an inch and it takes about 30-40 minutes for the thermometer to reach temp (i.e. have the stone fully heat loaded) AFTER the oven says it is at temp!
Hope some of you find that useful!
Jay
Thanks, Jay, for your excellent post. What you say makes a lot of sense. I'm anxious to see what happens to my bread when I really get my stone hot.
--Pamela
If you want to waste some dough, try putting a loaf of bread in your HOT oven on a COLD stone (it shouldn't break but...). You will end up with a loaf with a totally to almost raw bottom. By the time the crust is baked the heat will probably just be beginning to really reach the bottom of the bread. The loaf should be very dense (not enough heat getting into it to give proper expansion). A stone that is only marginally heat loaded should seal the bottom but could easily give similar results and a very pale "doughy" bottom. Obviously the paleness and underdoneness of the bottom goes away as the stone receives longer heating.
There may well be some breads and some ovens where an underheated stone is good but????
I am guessing a bit here, but I suspect the advantage of "overheating the stone" to 500 and then turning it down is that it compensates a bit for the fact the stone is not very big compared to a WFO or the oven volume it is trying to heat. Thus having it extra hot lets it put a bit more heat into the oven and elevate the temp of the oven a bit faster than if it had been heated to say 450. And that seems to be especially helpful on wet, artisanal loaves that cool the stone more than a smaller, stiffer dough might.
Jay
I don't want to waste good dough, but I might try an experiment cooking multiple loaves at different times, e.g., 30 minutes, 1 hour, 1 1/2 hours.
--Pamela
The challenge will be having them equally proofed. I will bet the difference between 30 and 60 minutes of heating will be somewhat subtle but visible to our critical bakers - assuming identical loaves and proofing (again, a bit denser, probably a tad "raw" on the bottom compared to the crust, less rise). I doubt you would see a difference between 60 and 90 minutes. The stone should be loaded (or very close) in an hour and any differences should be very minor.
If the 30 works, try 15! At some point it will not work. I guarantee! :o)
Jay
Calvel warns against moving the loaves as they bake as it is "one of the major causes of (bottom) crust burning". Presumably this would come about from moving the loaf to an area of the stone that had not lost heat to the loaf already. I try to be careful about repositioning the loaf to the same place when I rotate them midway through baking (when I remember to do that).
:-Paul
Hi Paul...I can see where you are right about that because...I do just the opposite when making several pizza's so I have a fast cooking pizza and perfect crust. I have to have the oven and stones up to full 550F. one hour pre-heat time works great! This way I can place one very large pizza..it will be completely crisped and deeply browned bottom and crust in no more than 7 mins. I can definately see the difference in time and temp. change on the stone when cooking the pizza..so I place it as much off the same spot where the last pizza cooked..this way the temperature is regained back and the stone has time to draw that inner retained heat back to the surface.."stabilize" it's called in wfo cooking! I have another smaller counter top convection,bake,broil, rotisseri,slow cook, you name it... oven that has a thinner pizza stone that came with it...the first pizza comes out okay..it only heat to apx. 450..the next pizza the crust is not as good..the stone has lost to much heat from the first pizza..it requires more pre-heat time. Pizza always tells me what's going on with the stone!
Sylvia
Good Question about turning off the oven. It MIGHT work but I fear the mass of the stone is too small compared to the volume of the oven. I would certainly welcome hearing about your results if you try it.
One of the things you learn with WFOs is that you can trade time for temperature (to a substantial extent). IF the stone holds enough heat to get the oven in the 375 range it may work.
RE: moving bread, once the bread starts to dry out it can burn pretty easily and moving it to 450 stone with it dry is a problem.
Good luck!
Jay
I have not read all the replies, but thought it is interesting that I just posted about NOT heating the oven for one hour, and getting excellent bread.
I know I am in the minority, but I refuse to use so much energy when I get excellent bread by heating my oven for much shorter time.
For instance, baking at 440F with a pre-heating of TEN minutes using a clay baker, gives me a loaf of great bread that was not too different from a bread baked on stone heating the oven for 45 minutes at 480F (I don't have side by side pictures, you will have to trust my word for it).
I simply cannot bring myself to keep an oven on for one hour = imagine if every household in the planet wanted to do that on a daily basis :-)
see page two of this link
http://bewitchingkitchen.wordpress.com/2009/07/27/the-bread-we-love/
I thnk that for pizzas the maximum heat possible at the bottom is important.
In that case, I have been using the outside grill as an oven, adding quarry stones on it. Since I've started doing it, I never fired my oven again for pizza. The grill gives a much higher temperature, the house is not heated up, and again, no need to keep the grill on for one hour before making the pizza.
Here is a thought about gas vs. electric ovens.
In an electric oven, when the thermostat turns off the current to the heating element, the heating elements remain hot for quite some time afterwards, acting in effect as a thermal flywheel.
When the flame in a gas oven is turned off, the only things radiating heat to the food are the interior walls. A baking stone can act as a thermal flywheel in lieu of the turned-off heating elements of an electric oven.