The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Baking Stone Too Hot

Conjuay's picture
Conjuay

Baking Stone Too Hot

I put together a propane fired pizza/bread oven from a used Bar-B-Que.  My first attempts indicate that the stone is getting much hotter than the upper half of the oven. Pizzas will get a bit of charring underneath while the cheese on top has hardly bubbled. Baguettes will hardly brown while the bottom is over crisp- bordering on hard.

There is space around all sides of the stone, approx 1.5" to 2", so the heat should be circulating.

The upper 'clamshell' of the BBQ is lined with mortar and fireclay to retain the heat, and I decreased the size of the upper chamber by adding firebrick to the "warming rack" that sits about six inches above the baking stone.

Did I simply go too large with the stone?  Do I need better (more) insulation up top?

Thanks for any advice,

Mike

 

 

 

Emelye's picture
Emelye

Maybe you have the burner under the stone on too high while baking?  With all the mortar and fireclay in there, which holds heat as well as insulating the chamber, maybe all you need to do once it's preheated long enough is to turn the burner down or even off.

PMcCool's picture
PMcCool

her mention of "preheated long enough" may be another factor for you to address.  Perhaps the upper portion of the oven, with all of its thermal mass, isn't hot enough with your current preheating tactics.  If that is the case, the pizza is being baked mainly by the direct heat from the flame below without any appreciable help from heat being radiated from the bricks and lining above.  Ergo, burnt crust and cold toppings.

Paul

mrfrost's picture
mrfrost

I have seen setups similar that have what is called a heat deflector. It shields the bottom of the stone from getting too much direct heat, while also helping route the heat up and around the stone to heat the upper part of the "cooker".

Doc.Dough's picture
Doc.Dough

I had the same problem about 30 yrs ago when I lived in a house with wimpy a/c in a hot and muggy climate.  It was too much to heat up the kitchen with the oven so I would make pita bread on the gas grill.  But it burned on the bottom before it got brown on the top.

The solution came in two parts. 

1. First there was way too much heat coming from below so I tried multiple ways to insulate the tiles (I was using 1/2" thick quarry tiles at the time). After two or three attempts I finally got an aluminum insulated cookie sheet (double layer), wrapped it in heavy foil and put it under the tiles.  That did fix the bottom side excess heat issue.

2. Any gas grill has to have a substantial amount of vent area to let the combustion products escape when the lid is closed and the burners are all on high (so it won't melt).  A byproduct of that design is that when you have the burners set to low so that you can hold 375°F in the box, there is more than enough vent area and any slight breeze will get in on the windward side and flush the hot air out - cooling the lid, the baking bread, and the tiles in the process.  The answer was to rig an outer insulation blanket to keep the radiant temperature of the lid up, a gap filler to cut down on the vent area, and a long probe thermometer so that I could monitor (to some extent) the hot air that accumulated under the bonnet.

It was good enough that I used it for four years in the summer.

I suspect that your problems stem from the same basic phenomena so perhaps this will stir you to a locally optimized solution.

Doc

Conjuay's picture
Conjuay

Thanks for all the responses...

After I wrote this, I took a long, hard look at the present setup. One thing I did notice was that the original grilling grids (which now hold the stone) are rather massive, almost resembling cast iron grids. I removed one, and centered the other to hold the stone. This does provide much more space around the edges of the stone for more air movement.

As this was an old (read "rusted") grill, I threw away the original baffles that act as flare guards while grilling. They were in rough shape, and, as I was intending to use a Fibrement stone (with the pan it can be purchased with), I considered the heat baffles redundant.  I will, however, add replacement baffles -all the big box stores carry them. An insulated cookie sheet, as Doc. Dough suggested would be ideal for this, except the stone (and pan) are larger than a standard cookie steet. But that shouldn't stop me from inverting a standard half pan in the fibrement's pan and setting the stone on top of that!

My third thought, as was also mentioned here, is to only fire up the two outer burners, as the stone may just be getting too much heat. The outer burners are relitively close to the stone's edge, and would tend to pass heat more easily around it, and cut the most direct heat source.

Thanks again, one and all, I'm going to try some of these ideas tonight... if it doesn't rain!

Mike

 

 

 

Doc.Dough's picture
Doc.Dough

Mike,
If you will stack two 1/2 sheets, you will get about a 1/4" air gap which you need. A single sheet will not give you enough effective insulation unless you stretch a layer of foil across the bottom to make a trapped air space - and I would be concerned that the foil would burn through.

If two sheets is not quite enough you can add a layer of foil between them (shiny side down I think) to create another radiation barrier. A zig-zag fold with 1" between the folds will keep it from becoming just part of one of the sheets from a thermal perspective.

Doc

Conjuay's picture
Conjuay

As luck would have it, I have a 1/2 sheet pan that is extra deep.  I put some water in that pan and nested the 'regular' pan into it.  Did two batches of  Kaiser rolls this morning and it worked great! (I didn't use the stone, just the nested pans.)

But over the weekend I did do some French breads using the stone and applying some of the suggestions posted here.

The oven is working much better using less heat (center burner off) and a longer preheat time. 

I will be baking quite a bit over the next few weeks, just trying to 'learn' this oven, but that's part of the experience, isn't it?

Doc.Dough's picture
Doc.Dough

Are you using the deep 1/2 sheet pan as a steam generator or are you using the water to hold down the temperature on the bottom of the second pan? I would expect that the water would boil away if it was in the oven during preheat, and it would prevent bottom browning if the pan that you are baking on can't get much above 220°F due to the water/steam below.

Doc

Conjuay's picture
Conjuay

I was using it as a steam generator but also to isolate the rolls. The pans were added at the same time and after the oven was preheated.  My first batch this way had too much water in the pan and the extra pan had to be pulled to cook the dough on the bottom. The second batch(and today's batch) used the same pans but with a measured amount of water- one cup. This seems to be the way to go for Kaiser rolls in this oven. The steam gives me the spring I need, and the second pan protects from scorching.

I will still be buying heat diffusers, however, because I think I will be able to control the heat distribution even better.