The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Black oven on the cards

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aneirin's picture
aneirin

Black oven on the cards

Hi everyone and greetings from the damp west.

Great website, lovely to read all of you breadheads in all of your eclectic variety. I'm planning on building myself an indoor brick black oven which I'll try to keep fired three days a week for small scale commercial production. I've just about settled on a design (eggshaped sole with 18 inch dome, 11.5 inch high door as according to Alan Scott) but I need to pick your collective brain about thermocouple positioning. I want to put in two, leading to either digital or mechanical thermometers so I get readings for dome and sole. Any tips on where to position these. What thickness of fire brick would you recommend for the sole and dome and does the thermal mass above the dome have any maximum thicknesses.

Thanks a lot for all your contributions while I was lurking, it's been an education

polo's picture
polo

...but I will give the details. I have three thermocouples placed in my barrel vault. One in the center of the hearth 1" down, one in the center row of arch bricks also 1" in, and one at the transition of the arch brick and the cladding. I have roughly 3.5" to 4" of concrete cladding over my arch brick.

I'm sure others will chime in here as well.

aneirin's picture
aneirin

Sounds like you've got the whole thing well sussed. I like the idea of one just at the junction of brick and cladding. Just wondering how thick the brickwork in the dome and sole are in yours. I'm planning on 6" in the dome and 8" in the sole or is this too skinny?

polo's picture
polo

The thickness of my brickwork is 4.5" in both my arch and floor. So from bottom up my oven hearth would be 3.5" vermicrete (for insulation), 3.5" concrete, and 4.5" firebrick. My vaulted arch would be 4.5" firebrick and 3.5" concrete covered with insulation.

Pioneer Foodie's picture
Pioneer Foodie

is insulation. Eight inches of masonry mass will still bleed heat if not insulated. Much better to go with four or five inches of mass and four inches of insulation.

polo's picture
polo

....didn't really answer your question. You should try and keep the thickness pretty well the same in the arch as it is in the hearth. To speak to Pioneer Foodies post above.......Yes, insulation is important, as is mass if you are baking multiple batches of bread. The heat has to pull from somewhere, insulation stores no heat. 

Pioneer Foodie's picture
Pioneer Foodie

From what I've heard on the Forno Bravo forum, thermocouples wear out even though the masonry doesn't, and there's no easy way to replace them. I have an infrared thermometer that I bought at Harbor Freight for about $30. It will measure surface temp anywhere in the oven.

polo's picture
polo

Type K thermocouples will eventually wear out, but with proper preparation and installation they will last a very long time. With a little forethought they can also be made replaceable. I believe an infrared is helpful, but will not give you any indication of how well your cladding is saturated with heat. This is especially true during the curing fires and the first few bakes. 

 In order to bake multiple batches of bread it will help Aneirin to know how well the oven is saturated, using thermouples will help shorten the learning curve.     

Pioneer Foodie's picture
Pioneer Foodie

The firebrick won't shed its soot until it reaches 700F. It won't reach 700F as long as it is bleeding heat into the mass. It takes time for the mass to store heat. If you go with heavy mass (as I did) the surface will tell you when it is ready to bake when it sheds its soot. Before that it is too cool as it is still bleeding heat out into the mass, and into the air if it isn't adequately insulated. If it is adequately insulated, saturation happens sooner, reflected by shedding soot. So now you say, "but you can't bake at 700F so you need thermocouples to read temperature." To which I say, cook a pizza on that 700F surface. When it takes 10 minutes for the pizza to cook rather than 5 then it is ready for bread. Or cast a handful of flour on the floor and count how long it takes to burn.

People baked fabulous bread for thousands of years without thermocouples.

polo's picture
polo

................you could install the thermocouples and use them until you have "learned" your oven's characteristics. The soot analogy doesn't work for me as my oven seems to "shed" (as you call it) the soot long before it's cladding is saturated. I know this because I installed thermocouples and can monitor the progress.

I agree that people have baked bread for thousands of years without the benefit of thermocouples or infrared thermometers. That is why I referred to a "learning curve". Wood fired oven heat mangement was probably a more widely held knowledge in the days before Wonderbread.

 Thousands of years ago people also lived in caves, rarely bathed, and probably ate with their mouths open. If they had Thermocouples back then, they probably would have used them. Unless of course "Forno Bravo BC" advised against it.

My apologies to aneirin for the hijacking of this thread. I am glad to be of help to you if I can.

ClimbHi's picture
ClimbHi

Alan Scott's book cover this pretty well. IIRC, he suggests one each in the center (thickness-wise) of the hearth and the dome. I elected to skip the thermocouples and I'm not kicking myself yet.  After a bit of experience, you'll get the hang of it without using any thermometer or thermocouples. As someone pointed out, once the dome soot burns off, you're around 900°. Once you reach that point, it's pretty much a matter of looking at your watch to keep the fire burning for a set time, which is different for each oven and you'll learn pretty quickly how much soaking time  your oven will need. Note that for a commercial setting, where the oven never really cools down, you'll get back up to temp quicker on subsequent firings.

As for firebrick, they're all pretty much 4" thick. You add to that by adding concrete on the outside of the oven brick. There's no single answer to how thick to make it -- thinner heats faster, so uses less fuel, but also cools faster, so not the best for a commercial use unless you plan to do a lot of fire-in cooking. If you expect to bake more than one or two loads on a single firing, count on making the masonry on the thicker side -- maybe 10-12" total (but you can get away with a bit less on the deck).

ClimbHi
Pittsburgh, PA

aneirin's picture
aneirin

As I said before it's always an education coming on this forum. I think I've got the hang of it now. I'll be putting a few thermocouples in probably, two in the centre of the dome and sole respectively and maybe one in just below the insulation layer. I'm thinking about laying them in narrow copper tube if I can, could make them replaceable when the time comes. I know it'll take a while to get to know this beast and I've talked to a few old bakers about soot burn off etc. but I'd like to record temperatures and burn times for the first year to lay a good foundation for the variety of baking I intend to do. Again thanks a lot people, I'll let you know how it goes when we get it off the ground.

polo's picture
polo

I also installed my thermocouples via copper tubing, It worked very well ans does indeed make them replaceable. There will more thatn likely come a time when you won't need the the input, but until then I think you will be happy with your decision.