How did I scorch a pizza in under 2 minutes?

[phoeniciansailor]

I have a Lodge 15" cast iron pizza pan which I tried using on my grill this afternoon. After 30+ minutes the pan was beautifully hot, about 650 degrees (F). Unfortunately, at this temperature the seasoning had vaporized. Oops.

I planned to follow a technique similar to that described in the thread "Pizza method page (cast iron pan + broiler)" (I would link, but new members are not allowed to, I guess). I would cook the bottom first, then immediately top and finish the pizza under the broiler. Using this technique on the stove top and in the oven, I've had moderate success, however I've been looking for ways to reduce the total cook time further (to reduce the dryness which can occur with more than 5 minutes of cooking). The grill seemed like the perfect solution.

I laid down my dough and in about 90 seconds it had puffed up beautifully, but the bottom was beyond burnt. This confuses me, because the floor of brick ovens are much hotter than my cast iron pan, yet pizzas cooked in them turn out just fine, and with longer cook times. Does anyone have suggestions as to what might have happened, or how my next attempt should be different?

Without seasoning on the pan, it did seem to stick quick a bit more, and those parts really burnt up. This could be the central problem? But I don't know how I can lubricate such a hot pan. Oil and extra flours won't work. In brick ovens, no lubrication seems to be used (other than ash, I suppose?).

By the way, my dough is 65% hydration, using high-gluten bread flour (14.2%), and cold-fermented in the fridge for a few days. I flour my dough liberally with AP flour while it's still a ball, then knock off all excess flour, stretch it out without additional flout, and transfer to the peel and then to the pan. Doesn't seem like much excess flour hangs onto the dough this way, but I could be wrong.

[scott123]

1. If you don't have an IR thermometer, get one.  It's really difficult to do pizza on a grill without it.

2. Iron is quite a bit more conductive than firebrick.  That means that it can take whatever heat it's holding and transfer it far more quickly than firebrick can.

[PizzaHog]

Welcome to the forum phoeniciansailor
I have experimented this method a lot so here are my observations for whatever they are worth, which concur with what Scott123 posted.

I would cook the bottom first, then immediately top and finish the pizza under the broiler. Using this technique on the stove top and in the oven, I've had moderate success, however I've been looking for ways to reduce the total cook time further (to reduce the dryness which can occur with more than 5 minutes of cooking).

Some have success with this but not me.  I have the best results when I remove the cast iron from its heat source, place it directly under and as close a poss to the pre-heated broiler, then place the fully topped pie.  The entire bake is done in one step with the cast iron providing only the residual heat it already contains while the broiler pounds heat from above.  This averages just over a 2 min bake for me and eliminates the pie being on the cast iron for twice as long so the bottom is less likely to burn.
Even then, I have found the max temp I can hit with the cast iron can still be too high even with the short bake time.  So a IR thermo as Scott suggests is a huge help.  Otherwise you can try and accomplish the same by limiting your preheat.  I can hit between 650-700 but have found 600-650 works much better.
I have had the least sticking problems by seasoning the cast iron with oil.  Yes, it does smoke during the preheat and one would think it all burns off.  But for whatever reason still helps a lot.  Sometimes the pie does not stick at all and when it does it is usually just a little.  I carefully re-season between pies as the pan does cool down quite a bit during the bake.
I also rotate the pie about 30 degrees twice during the bake to try and even out the broiler heat.
Again just my case, but I found a slightly lower hydration improved the bake time and final result as compared to what works best with my stone.
Hope this helps and good luck.  If you get it to work it is pretty cool and a blessing during the hot summer months.




 

[IndyRob]

I too have done the cast iron on the (gas) grill thing and ruined the seasoning.  But not for pizza, for steaks.  I got my pan up to 765 degrees (IR measured) and seared seasoned beef fillets for a minute on each side (the amount of smoke is epic) and tranferred them to oven safe plates and put in the 425 degree oven for 7 minutes.  Perfect - for the steaks, not the pan.  I'd like to find a piece of stainless steel plate to use for this.

For pizza, I tried a pizza stone directly on top a charcoal grill and got a very similar result to what you describe.  Totally black on the bottom (although in a promising sort of way) and not cooked on top.  My pizza stone didn't survive a second attempt.  It cracked right down the middle.

The problem is too much heat on the bottom and not enough on top.  From what I've seen, wood or coal fired ovens generate heat on the deck in a low ceilinged oven.  The heating of the floor is done more by ambient heat rather than radiant heat from below like our grills.  The ~700 degrees these ovens do is pretty much all-around heat.  I think I've read that New York pies don't stay in those ovens for more than 2-3 minutes.

There are purpose built pizza stones for grills that use stainless steel legs to raise the stone of further.  But the real solution looks to be a heavily modded Weber grill highlighted in the Pizza News forum PizzaHacker post (http://www.pizzamaking.com/forum/index.php/topic,10057.0.html).  Short of that, you'd have experiment with indirect heat, lower heat and/or some sort of radiant heat reflection device over the pizza.

[phoeniciansailor]

Thanks for the information so far. It got me thinking about the conductivity of metals. I can start to see how a very conductive metal like cast iron at 650 degrees could scorch a pizza by very quickly dumping too much energy into the crust, whereas a less conductive material like fire brick or Fibrament at the same temperature would not.

But now I'm getting myself confused trying to understand the practical differences between a) baking at a lower temperature on a highly conductive material for a short amount of time, and b) baking at a higher temperature on a modestly conductive material for a longer time. Perhaps in theory they do equal out in some way, in terms of heat transfer. But I guess, in practice, that there's going to be a "too fast" (scorched and raw in places) and a "too slow" (dried out), depending on the thing you're trying to bake. Perhaps it comes down to the conductivity of the dough.... You can't bake a french loaf in 10 seconds no matter what.

If I decide to shoot for a modest 4-minute bake, I wonder if I could work out approximately the right temperature to heat my cast iron to, given its particular conductivity. Hmm. It's obviously less than 650 degrees. The temperature might even be within the operating range of my oven (which would spare me endlessly re-seasoning my pan).

If I could get the bottom of the crust perfected, then I could move on to figuring out how to get the top cooked perfect in 4 minutes as well. It might also be possible in the oven. I've been thinking about ordering a 15"x20"x0.75" Fibrament stone to sit just above the pizza and act as a sort of "dropped ceiling" and heat store...

[Jackie Tran]

I've been thinking about ordering a 15"x20"x0.75" Fibrament stone to sit just above the pizza and act as a sort of "dropped ceiling" and heat store...

Some good discussion going on here.  I've had the same issue with the bottom outcooking the top whether it's in my home oven or in my primo ceramic grill. 

The one constant is that I've been using my (food safe) glazed ceramic stone and just last night I questioned myself if a glazed stone could possibly behave much differently from an unglazed stone in transferring heat. Could it be that the glazed stone is playing a part in transferring heat too quickly? 

In my primo ceramic grill, I've also been experimenting with a dropped ceiling to replicate a mini 2 stone oven inside my primo.  From what I've notice so far, you may be better off using a more conductive material above the pie such as your CI pan or some metal plate with a stone over that to prevent heat transferring through.  This may work better for reflecting heat than using just stone alone.   

[Tampa]

A few comments
- Keep in mind that an iron pan performs quite differently from a stone.  Besides the obvious conduction difference (steel conducts better than stone - put your finger on it and see, not), the steel holds moisture/steam between the hot surface and the pie.  Stone is more porous.   I don't know much about glazed ceramic, but suspect it is not very porous and may hold the steam as well.  Due to the differences between iron and stone, and the success of stone, I'd stick w/ stone.

- There is a lot of experimental knowledge in reading through the "little black egg" thread.  Thin pizza stones tend to break.  Convection is important over the top of the pie to get proper cooking, but it doesn't matter much if the hood is stone, metal, perlite, or whatever.  The hot air convection currents flowing directly over the pie and exiting do the trick.

- I've run a bunch of experiments putting various hoods inside inside a grill (http://www.pizzamaking.com/forum/index.php/topic,10241.0.html).  Take note of Reply 7 because it will give you a good idea what to expect in terms of temperature vs. configuration tradeoffs.
Dave

[scott123]

- Keep in mind that an iron pan performs quite differently from a stone.  Besides the obvious conduction difference (steel conducts better than stone - put your finger on it and see, not), the steel holds moisture/steam between the hot surface and the pie.  Stone is more porous.   I don't know much about glazed ceramic, but suspect it is not very porous and may hold the steam as well.  Due to the differences between iron and stone, and the success of stone, I'd stick w/ stone.

Porosity plays no role in moisture absorption.  When you're dealing with 500+ degree temps, any water in the dough evaporates before the stone can actually absorb it. I've used incredibly porous firebrick and non porous soapstone, and, beyond conductivity differences, the results were identical.

[Tampa]

Scott123: Really?  Porosity makes no difference?  Thanks for sharing your results.  I figured that the moisture in the skin would flash when it touched the iron pan and the resulting steam would increase heat transfer to the pie and may cause the scorch.

What differences did you see between firebrick and soapstone (and any other test you've tried)?

Not to belabor the point, but in the interest of pie science, if there were "conductivity differences", how do you know that they were not attributable to differences in moisture present?  I know they make perforated pizza pans, different from a cookie sheet, and I thought part of the reason was to let the moisture escape.  I really would like to get the right answer even if it is not mine.

Dave

[PizzaHog]

But now I'm getting myself confused trying to understand the practical differences between a) baking at a lower temperature on a highly conductive material for a short amount of time, and b) baking at a higher temperature on a modestly conductive material for a longer time.

One pizza theory is that everything else being "equal", the shorter the bake time the better the final result.  One could consider the method of having to add oil (or other additions) to the dough for longish bake times to maintain moistness as support for this.  For those that agree, lowering bake times (= more heat or conductivity) is the priority.  Our reality is nothing is really "equal" so great pizzas can be had many ways as this forum demonstrates.  Having said that though, my favorites and best I have pulled off seem to follow this theory.

I figured that the moisture in the skin would flash when it touched the iron pan and the resulting steam would increase heat transfer to the pie and may cause the scorch.

Steam at atmospheric pressure is 212f.  Even in a pressure cooker at 15 psi it only hits about 250f so from a temp only standpoint it does not seem this is the cause of the scorching.  Steam can actually work as a temp limiter or insulator in this capacity which is perhaps the reason for the pan with the holes in it.
Most interesting discussion which makes me wonder about all the factors at play here.

[phoeniciansailor]

Most interesting discussion which makes me wonder about all the factors at play here.

I'm imagining a Minority Report-esque interactive chart, with sliders for each factor (conductivity and thermal mass of the floor, hydration of the dough, thickness, cooking time, etc.), and each slider is connected to every other, all moving in synch, always balancing out to show the formula for the perfect pizza.

[Tampa]

Good point PizzaHog.  Steam could be a limiting factor, but it is complicated, especially when the steam dissipates.  I've noticed times when I throw on a hot stone, the pizza skin sticks to the surface, almost sucked down.  Once the pie is separated from the stone, it cooks fine - but if I don't catch it early, the crust burns.

I out of my league questioning Scott123.  If you check out posts at http://www.pizzamaking.com/forum/index.php/topic,10973.0.html, especially starting at Reply 12, and then on page two.  He has a lot of experience in this area.  It is hard to read all the prior relevant discussion on a topic..

[PizzaHog]

I'm imagining a Minority Report-esque interactive chart, with sliders for each factor (conductivity and thermal mass of the floor, hydration of the dough, thickness, cooking time, etc.), and each slider is connected to every other, all moving in synch, always balancing out to show the formula for the perfect pizza. Smiley

Now you're onto something ps!  Unfortunately we are prob lacking a bit of the technology needed although we certainly have the knowledge and database - that would be Pete-zza! 

I out of my league questioning Scott123.  If you check out posts at http://www.pizzamaking.com/forum/index.php/topic,10973.0.html, especially starting at Reply 12, and then on page two.  He has a lot of experience in this area.  It is hard to read all the prior relevant discussion on a topic..

I was not following that thread closely enough but am glad you pointed me back to it Tampa as Scott123 referred to this link http://www.pizzamaking.com/forum/index.php/topic,5645.msg47871.html#msg47871 which I had never run across before. So I did some looking about and I think I found our scorched bottom culprit.

FibraMent
Density: 1.762 g/cm3
Thermal Conductivity: 0.69183088225 W/m-K

Cordierite
Density: 2.6 g/cm3
Thermal Conductivity: 3.0 W/m-K

Soapstone
Density:  2.98 g/cm3
Themal Conductivity:  6.4 W/m-k

Firebrick 21% - 40% alumina
Density:  3.7 - 4.5 g/cm3
Thermal Conductivity:  0.98 - 1.13 W/m-k

Cast Iron
Density:  6.8 - 7.9 g/cm3
Thermal Conductivity:  46 - 78 W/m-k

The variance is due to "cast" iron not being standardized and the numbers I found other than those provided by rednovember may not be in accordance with recognized testing standards. 
But if soapstone is, as one article I read describes it, a thermal battery, then cast iron is a thermal nuclear 900 pound gorilla reactor in melt down.
So I will be looking for soapstone as Scott123 so kindly pointed out while trying some new tactics with my cast iron.

[Tampa]

I agree that the numbers show cast iron has a thermal conductivity which is an order of magnitude greater than conventional pizza stones - and would suspect conductivity caused the char.

Reading the early posts by rednovember and Scott were humbling.  What a wealth of knowledge this forum can muster.

[phoeniciansailor]

agreed, i've learned much in the last week. i've been reading until my brain hits capacity, then i let it soak in, and come back for more. there is real value in understanding the science, like the conductivity values of the various media, as well as the real-world "reviews", such as scott's "ratings" of the media (where he gave soapstone a 10, cordierite a 9, etc.) i hope all these nuggets of wisdom are getting archived, and maybe even collected into some single "best practices" document.

i did another pizza on the cast iron last night, this time all at once on the iron and under the broiler (rather than two-stepping it) and it really wasn't too bad. the broiler out-paced the iron, but my dough was also still a little bit cold. i think with practice i can develop a real intuition for the process with whatever materials i have available (which i hear repeatedly here).

i located a soapstone dealer here in austin, texas, (dorado soap stone; you can google it). i'm getting a 15"x17"x1.25" slab for my oven (and bbq) cut out of scrap/remnant. the piece i was offered was actually more like 20x22, but my oven and grill are only human-sized. $75 for the stone and cutting service, which might be expensive (or not). so far they've been nice to work with. i should talk to them about getting into the custom pizza-stone distribution business. they said that they have lots of scrap, but i have no reason to think that they ship or could handle custom orders other than in person and Pete-zza has indicated in another thread (see below) that they're willing to ship for $50 or so (or less, in some circumstances).

[Pete-zza]

i located a soapstone dealer here in austin, texas, (dorado soap stone; you can google it). i'm getting a 15"x17"x1.25" slab for my oven (and bbq) cut out of scrap/remnant. the piece i was offered was actually more like 20x22, but my oven and grill are only human-sized. $75 for the stone and cutting service, which might be expensive (or not). so far they've been nice to work with. i should talk to them about getting into the custom pizza-stone distribution business. they said that they have lots of scrap, but i have no reason to think that they ship or could handle custom orders other than in person.

As I noted at Reply 24 at http://www.pizzamaking.com/forum/index.php/topic,10224.msg89833/topicseen.html#msg89833, it appears that Dorado will ship the soapstone pieces, at least to the Dallas area. Whether they will ship outside of the state is not something I asked. It looks like you were quoted about the same base price that I was quoted.

Peter

[PizzaHog]

What a wealth of knowledge this forum can muster.

Agreed, incredibly so.
phoeniciansailor
Sounds like you're getting closer with the cast iron, just have to find the right starting temp.  SCORE ! on the soapstone!  Congrats and let us how it works out.

[Tampa]

Check this out.  Dr Bob and I ran a test to see if surface porosity made a difference in his commercial pizza oven per the comment:

Porosity plays no role in moisture absorption.  When you're dealing with 500+ degree temps, any water in the dough evaporates before the stone can actually absorb it. I've used incredibly porous firebrick and non porous soapstone, and, beyond conductivity differences, the results were identical.

We put a very thin aluminum cookie sheet over one-half of the cordierite stone, heated everything for about an hour to a steady state temperature of 685F and threw in a pie.  Here were the results.
 
Pizza inside oven – half on stone half on thin aluminum:

Pizza removed from oven – note finger pointing at surface less cooked
 
Big difference in bottom char

Observations:
We think porosity makes a big difference in the result.  The only difference between the two sides was a thin aluminum plate – otherwise both sides had the same start temperature, same underside burner, same top-side burner.  Overall, the thermal mass was comparable between the two sides as most of the heat is stored in the stone.
I think Hog had it right

Steam can actually work as a temp limiter or insulator in this capacity which is perhaps the reason for the pan with the holes in it.

The effect of a foil moisture barrier is considerable throughout the pie.  As you can see from the photos, the bottom and top are less “done” when foil is present.  Also, the gum line, i.e. the doughy part between the bottom crisp and sauce, was significantly thicker on the foil side than on the raw stone side.
The results suggest that once the pie was placed on the foil, moisture in the dough flashed into steam and acted as an 212F insulator on the bottom.  That moisture kept the center dough and upper cheese area from cooking in spite of the glowing upper element.

[scott123]

Tampa, although I applaud your efforts to get to the bottom of the perceived mystery, I must point out a few errors in the methodology.

For reference purposes, I think it will help to reiterate PizzaHog's very helpful chart from above, and, at the same time, add values for two other materials (in bold):

Air
Thermal Conductivity: 0.024 W/m-K

FibraMent
Density: 1.762 g/cm3
Thermal Conductivity: 0.69183088225 W/m-K

Cordierite
Density: 2.6 g/cm3
Thermal Conductivity: 3.0 W/m-K

Soapstone
Density:  2.98 g/cm3
Themal Conductivity:  6.4 W/m-k

Firebrick 21% - 40% alumina
Density:  3.7 - 4.5 g/cm3
Thermal Conductivity:  0.98 - 1.13 W/m-k

Cast Iron
Density:  6.8 - 7.9 g/cm3
Thermal Conductivity:  46 - 78 W/m-k

Aluminum
Density:  2.7 g/cm3
Thermal Conductivity:  250 W/m-k

When you open the door to put the pizza in, the aluminum is so conductive that any heat that may be stored in it is lost. More importantly, though, looking at the photo, there's an air gap between the aluminum and the pizza stone.  Air's incredibly poor conductivity causes very little heat to transfer from the preheated stone to the aluminum sheet.

The form fitting nature of aluminum foil would make it more suitable for an experiment like this, although, even then, it will have creases that will most likely trap some air, which will create a little insulation.  Still, I think the differences should be minimal.

[Tampa]

Hopefully no one is reading this post because I'm eating crow again (mostly).  Dang Scott!

I re-ran the test using aluminum foil on half of the pizza and the results were ... well it's complicated.  Take a look at the pictures.  Unlike the initial cookie sheet result, this time the underside char was comparable between the two sides.  I did not expect that.  Props to Scott for calling me out.

But if you look closely at the underside photo, you'll notice that the foil side looks more like a pancake and the stone side looks like a pizza.  We had three tasters comment on the results.  The foil side was: "less crispy", "less puff", and "more soggy/chewy".  Everyone preferred the stone side of the pie.

I really want to blame it on Dr Bob because he was the egg-head that dreamed up this experiment in the first place - but I've had pizza three days in a row so what's not to like about that.

Dave