pizza stone placement

[canadave]

A question for the audience:

I use a pizza stone in a normal electric oven that goes up to 555 degrees (that's the temp I cook at).  I've always used the stone on the lowest possible rack, because that way the stone is most directly absorbing the heat coming up from the bottom oven element.

But now I want to try to bake my pizza more quickly.  If I can elevate the stone to the highest oven rack, then I'll be able to take advantage of higher air temperatures there, and the pizza toppings should bake faster, right?  In fact, I could even set my oven to "Broil", and that should *really* bake the pizza toppings quickly (intense heat coming straight down from the oven ceiling element).

But baking the pizza toppings quickly is only part of the story--there's also the bottom crust to consider.  I guess my main question is: if I elevate the stone to the highest rack in the oven, will the stone not get as hot as if it was on the lowest rack?  Or does it just mean it'd take longer for the stone to reach the same maximum surface temperature of 555 degrees?  There's no sense in my being able to bake the pizza toppings quicker, if it means that the stone will be cooler and the bottom crust of the pizza won't bake as quickly.

Thanks!
Dave

[canadave]

Anyone?...Anyone?...Bueller?...Bueller?.......
 

[Pete-zza]

Mr. Stein,

I was feeling sick today so I am at home. But since you are my favorite teacher I wanted to help you by researching your question. From what I have been able to find at the wonderful pizzamaking.com forum, most members seem to place their stones at the lowest oven rack position, for the reasons you mentioned. When Tom Lehmann is asked about this matter by home pizza makers, he usually recommends that the stone be place in the middle oven rack position. Steve discussed using the top oven rack position in this thread: http://www.pizzamaking.com/forum/index.php/topic,2503.msg21716.html#msg21716. I hope this helps.

Ferris (Bueller), cough, cough

[canadave]

Ah, Ferris, my favourite student, glad you at least phoned in if you're sick   Usually you just drive around with your pals.

Thanks for the reply.  I did see that post through a search, but it left me with more questions than answers.  I guess my first question is: when the person says the stone was 600 degrees even though the oven temp was set to 550, I'm wondering how something can be hotter than the maximum temperature it's being heated at?  Doesn't that violate the universe's laws of thermodynamics or something like that?

Second, the posts in that thread never really addressed my question of whether heating the stone on the top-most rack, from the top oven element, with the thermostat set to "Broil", will get the stone hotter than putting the stone on the bottom-most rack, heating it with the bottom oven element, and setting the thermostat to 550.

What do you think?

[November]

I'm wondering how something can be hotter than the maximum temperature it's being heated at?  Doesn't that violate the universe's laws of thermodynamics or something like that?

Uh, no.  Ever gotten into a hot car and found that the steering wheel was much, much hotter?  Thermal capacitance (specific heat capacity) is the key to your quandary.

http://en.wikipedia.org/wiki/Specific_heat_capacity

- red.november

[pizzoid]

Not thermal capacitance. In this situation, the stone is being heated by Infra Red radiation more than convection or conduction, and because it's a much better absorber of this radiation than the air in the oven, it can get a lot hotter in the short term, until things start reaching equilibrium.  This is why the recommendation for the stone on the bottom-most rack. The stone will heat faster, and higher. Because it's so complex a balancing act and ovens are so different, some ovens will cook a pizza better with under an hour of preheating the stone, because the stone can be well over the chosen thermostat temperature. I find that in my oven, leaving the door open for a longer time while pulling the done pie, before closing the door to preheat for the next pie  gives me a rebound in the stone temperature because the air leaks out, the oven thermometer drops, then the element comes back on driving more IR into the stone and kicking it back up higher.

- Al

Uh, no.  Ever gotten into a hot car and found that the steering wheel was much, much hotter?  Thermal capacitance (specific heat capacity) is the key to your quandary.

http://en.wikipedia.org/wiki/Specific_heat_capacity

- red.november

[Pete-zza]

Second, the posts in that thread never really addressed my question of whether heating the stone on the top-most rack, from the top oven element, with the thermostat set to "Broil", will get the stone hotter than putting the stone on the bottom-most rack, heating it with the bottom oven element, and setting the thermostat to 550.

What do you think?

Canadave,

November has given you the answer to your questions but I might add that my oven, a fairly standard Whirlpool oven, will not allow me to keep the broiler on all the time. The broiler kicks in and out depending on whatever temperature limit is monitored by the oven. The instructions for the oven also say not to use the broiler with the oven door shut. Consequently--and since I only have a cheap oven thermometer--I don't really know whether my stone will be heated to a higher temperature when placed adjacent to the broiler element versus the lower heating element. But there is no question, for the reasons mentioned by November, that the stone will be hotter when placed on the top and bottom oven rack positions than in the middle. I'm sure that several of our members who have infrared thermometers have taken the types of measurements that will do a better job of answering your questions than I.

Peter

[canadave]

Thanks everybody for the replies.  An interesting discussion.  Pete, now that I read what you've just written, your observations square with mine regarding the broiler.  It started out red-hot, and then when I checked on it a few minutes later, it was back to its normal black colour (it was impossible to tell if it was still generating heat...I bravely stuck my hand in for a few seconds, but it just felt hot...no way to tell if the heat was just ambient heat or heat coming from the top element).

The bit about thermal capacitance and specific heat raises another question for me.  Is there some other substance we could use in the oven--something other than quarry tiles--that has properties such that the specific heat is a lot lower? i.e. its temperature would rise higher than quarry tiles if both were exposed to the same oven element?

--Dave

[pizzoid]

Wouldn't that be self-defeating? The lower the specific heat capacity of the "stone", the more it will drop when you slap a room temperature pie onto it. Low enough, and the pie won't cook, because the stone's temperature has dropped drastically, yet the air in the oven controlling the thermostat will either not drop so much, or will rewarm quickly from the oven walls. The equivalent of the lowest specific heat capacity device would be a thin pan, anodized black, wouldn't it?

My feeling would be to get something with the highest specific heat possible, then make the stone very large (covering most of the oven bottom) so it can absorb lots of IR. Not sure how that would translate for what you're all thinking of for top heating.

I wonder if anyone makes a stone/slab with built in heating element that could be used as a pie turbocharger, getting the cooking surface to 800 in a 500 oven?

- Al

The bit about thermal capacitance and specific heat raises another question for me.  Is there some other substance we could use in the oven--something other than quarry tiles--that has properties such that the specific heat is a lot lower? i.e. its temperature would rise higher than quarry tiles if both were exposed to the same oven element?

--Dave

[November]

Not thermal capacitance. In this situation, the stone is being heated by Infra Red radiation more than convection or conduction, and because it's a much better absorber of this radiation than the air in the oven, it can get a lot hotter in the short term, until things start reaching equilibrium.

pizzoid,

How hot something gets has little to do with its ability to absorb IR radiation, or any other form of thermal energy.  How hot something gets is directly proportional to its specific heat capacity coupled with its thermal conductivity.  Copper can absorb IR radiation better than platinum, but because of it being a better thermal conductor, it cannot get as hot as platinum because it is losing heat almost as fast as it's gaining it.  The same goes with capacitance.  It doesn't matter that stone can absorb more IR radiation than air.  What matters is that it can hold on to that thermal energy better than air.

- red.november

[November]

The lower the specific heat capacity of the "stone", the more it will drop when you slap a room temperature pie onto it.

I think you may be confusing capacitance with conductance.

[November]

Is there some other substance we could use in the oven--something other than quarry tiles--that has properties such that the specific heat is a lot lower? i.e. its temperature would rise higher than quarry tiles if both were exposed to the same oven element?

Yes, there is, but I'm not sure how much difference you're looking for.

pizzoid,

He was talking about a lower heat capacity for his tiles, not his stone.  At least that's what I think he's talking about.  Please confirm, canadave.

[Pete-zza]

Canadave,

I am certain that there are different materials used for baking purposes that have different thermal conductivities and heat capacities. In fact, I recall that one of our members provided a link to that kind of information. However, the more important consideration in your case may be what you are trying to achieve. For example, if you want to bake only a single pizza, you should be able to heat a single layer of tiles to the desired temperature and so long as you don't open and shut the oven door too much, be able to satisfactorily bake your pizza. But if you plan to make several pizzas in succession, you may want to use a double layer of tiles. This may require a longer preheat time but the heat will be retained longer. Or you can retain thermal capacity in the oven by using two pizza stones, one above the other. Again, it will take a longer time to get the two stones up to the desired temperature, but the heat will be retained longer. I have seen some members who have built mini-ovens within their home ovens, using multiple stones and tiles and the like, and it can take a couple of hours to heat up the mass of material. Professionals using deck ovens get around the heat retention and heat recovery problem by using massive slabs of thick material. As you might expect, it takes a long time to get those ovens ready for use.

Peter

[canadave]

Yes, there is, but I'm not sure how much difference you're looking for.

pizzoid,

He was talking about a lower heat capacity for his tiles, not his stone.  At least that's what I think he's talking about.  Please confirm, canadave.

What I was talking about was the possibility of something other than quarry tiles, which I could put bake my pizzas upon, that would absorb the 550 degrees of my oven, but wind up getting hotter than the tiles do right now (which, according to others, is usually around 600 degrees).

In other words, if there was some substance that I could put in the oven, turn on to 550 degrees, and then have the substance's temperature wind up being 800 degrees or something equally high, after some period of time.  Does that make sense?

[canadave]

Pete--yeah, I think I'm talking about doing just one pizza at a time, not several at once.  In my case, I'm not so much concerned about holding heat longer...I'm thinking of the prospect of getting the temperature of the cooking surface higher than mere quarry tiles will allow.

[pizzoid]

I disagree (I think). In this specific instance of an oven and pizza cooking surface (tiles, stone, whatever), the only way the cooking surface can get to higher temperature than the thermostat is by having a good IR absorbtive surface (I find burned spilled sauce and cheese on the stone to be an effective means of increasing IR absorbtivity, but one that can lead to breakage  ). The only thing getting over the thermostat temperature is the heating element, and the only way to get that energy to the cooking surface is radiation. The other pathways involve first getting the transfer medium (air)  up to the thermostat trip value....

The conductivity of the cooking surface material, once it's up to temperature, is then crucial to getting that energy out of the surface and into the cooking crust. It's also important depending on where the heating element is - depending on if you're trying to get the heat through the stone from the bottom or not. In a top element situation like Canadave is asking about, the pie on top kinda gets in the way!

The capacity determines how much energy has been stored in the cooking surface during preheat and how long it will flow into the pizza.

Although the cooking surface can hold onto the energy better than the air, I don't think that's necessarily good. Once the pizza is on the surface, the conductivity between the pie and cooking surface is the primary thing. (Although that probably involves convection of superheated steam for some of it on the very small scale.) Getting the oven air reheated because most of it went out of the oven is then the secondary concern (or in a top heat situation using the radiation from the top element to directly heat the pie). Balancing the primary and secondary heating gives you the good pie.

Lets see, a 18" square of copper, 3/4" thick, for an experiment........  $777.14 from McMaster Carr.  Not including shipping or surface treatment.......... Ow, Ow, Ow.

I think we're mostly trying to voice the same things, but are rushed for time. And "simple" ovens are much more complicated than we normally think.

In any case, the only reasonable (cheap) suggestion I can think of for Dave to try is to get another set of tiles, heat them until dry, cool them, lightly coat them with oil _both_ sides, then "season" them in his oven until they blacken. That will allow them to be better IR absorbers, and should give him a higher temp. Especially if he keeps opening the oven door to spill out the air, causing the element to keep turning on.  And keeps them close to the heating element. The tiles will, of course, no longer have an unsealed surface.

pizzoid,

How hot something gets has little to do with its ability to absorb IR radiation, or any other form of thermal energy.  How hot something gets is directly proportional to its specific heat capacity coupled with its thermal conductivity.  Copper can absorb IR radiation better than platinum, but because of it being a better thermal conductor, it cannot get as hot as platinum because it is losing heat almost as fast as it's gaining it.  The same goes with capacitance.  It doesn't matter that stone can absorb more IR radiation than air.  What matters is that it can hold on to that thermal energy better than air.

- red.november

[November]

What I was talking about was the possibility of something other than quarry tiles, which I could put bake my pizzas upon, that would absorb the 550 degrees of my oven, but wind up getting hotter than the tiles do right now (which, according to others, is usually around 600 degrees).

In other words, if there was some substance that I could put in the oven, turn on to 550 degrees, and then have the substance's temperature wind up being 800 degrees or something equally high, after some period of time.  Does that make sense?

Yes, it makes sense now, but you initially said you were using a pizza stone.  So when you mentioned quarry tiles (plural) it sounded like you use quarry tiles to surround your oven, and that's what you want the temperature of lowered so that the difference between the tiles and the stone increases, resulting in a hotter stone relative to the surrounding tiles.  In the case you are now describing, you do want a stone (quarry tile) with higher specific heat capacity.  Getting up to 800 degrees is a bit of a challenge though.  It would require a very expensive engineered material.

- red.november

[November]

pizzoid,

Before reading your entire post, I can tell right away you're not factoring in time.  I'll comment more in an edit.

EDIT:

"the only way the cooking surface can get to higher temperature than the thermostat is by having a good IR absorbtive surface"

Again, how hot a material gets has nothing to do with how it's heated, only with how much heat it can retain and conduct.  The time factor I mention above is what you are missing in your analysis.  You can spend a thousand years trying to bombard a pure black body with IR radiation, but if it contains very little mass, it has very little capacity for thermal energy, and consequently will not get hot.  IR absorption only relates to how fast the material heats up, because it has another source of energy to feed on, not how hot it can get.  Once a material is at "full" thermal capacitance (which will take longer if not absorbing IR), it doesn't matter that it can absorb heat from any source, because at that point there is an equilibrium between capacitance and conductance.

"The capacity determines how much energy has been stored in the cooking surface during preheat and how long it will flow into the pizza."

That half right.  Heat capacity and thermal conductivity determine how long it will transfer heat to the pizza.

"Once the pizza is on the surface, the conductivity between the pie and cooking surface is the primary thing."

Yes, but not the way you are describing it.  You don't want the pizza to get burned on the bottom sooner than the top is finished.  You only want enough conductivity in the material to brown the bottom at the same rate as the top.  You want enough capacity to keep the temperature up throughout the entire baking process.

- red.november

[canadave]

Yes, it makes sense now, but you initially said you were using a pizza stone.  So when you mentioned quarry tiles (plural) it sounded like you use quarry tiles to surround your oven, and that's what you want the temperature of lowered so that the difference between the tiles and the stone increases, resulting in a hotter stone relative to the surrounding tiles.  In the case you are now describing, you do want a stone (quarry tile) with higher specific heat capacity.  Getting up to 800 degrees is a bit of a challenge though.  It would require a very expensive engineered material.

- red.november

Yes, sorry about that--in my mind, I tend to equate pizza stone with quarry tiles arranged in a square.  To clarify further--I have four 8x8" quarry tiles, arranged in a square (which of course is 16" x 16"), in a single flat layer.  The tiles are 1/2" thick.

Getting up to 800 degrees is a bit of a challenge though.  It would require a very expensive engineered material.

Exactly...and that's the million dollar question that I'm asking   Is there a substance out there that would do that, but wouldn't be expensive?   If so....woohoo!

[pizzoid]

 In the case you are now describing, you do want a stone (quarry tile) with higher specific heat capacity.  Getting up to 800 degrees is a bit of a challenge though.  It would require a very expensive engineered material.

- red.november

Hey! There you go!

Just make the "stone" out of Sodium. Slap a high hydration dough on it, and it will get way over 800 degrees   

Don't even need to preheat (and can't). And cooks the pie in 8 seconds. 

Ok, I GOTTA get back to work.....

- Al