Why does bottom of my bread loaves burn?

[Spunkoid]

Re: Why does bottom of my bread loaves burn?

Your bread is burning on the bottom simply because the floor of the oven where it is sitting is too hot causing the bread to burn.
I started my oven late one evening, after it got up to temperature, I scraped the bed of coals to the side. The fire brick floor of the oven where the coals had been sitting was glowing red hot. You need to move the coals over and let the oven floor cool down.

[SableSprings]

Re: Why does bottom of my bread loaves burn?

Mike, how did you do the temperature profile? Did you just open the oven at each hour and test it with a laser thermometer? Or did you have some other method?

BTW, I think it is a great idea for people like me who are new to do that kind of profile. It should help a lot. Thanks,

Yes, for my oven temp profile I just use the laser/IR gun to get the hourly readings. In my mind, the best results are achieved when you are consistent where you take the readings and make uniform time units (hourly) between readings. I choose an area of the hearth that is representative of the area on which I intend to bake and then clear any ash/coals. I use a pulsing fire to load the oven, so I take my hearth and dome readings on the hour when my fire is at its lowest point. Using the IR gun from Forno Bravo I get an average temperature of those areas before adding more wood.

I'm not sure if everyone knows this, but if you hold down the trigger of that "orange grip" IR gun and take a slow sweep across the cooking surface, you can use one of the top control buttons to cycle through max, min, and average reading of the gun's sweep. After getting the hearth & dome readings, I add another 3-4 chunks of wood to pulse more heat into the oven. I continue to take temp readings on the same areas after clearing out the fire and equalizing/baking. My hourly data is put into an Excel spreadsheet to create the temp profile/graph.

[poweredbypizzas]

Re: Why does bottom of my bread loaves burn?

Mike, how did you do the temperature profile? Did you just open the oven at each hour and test it with a laser thermometer? Or did you have some other method?

BTW, I think it is a great idea for people like me who are new to do that kind of profile. It should help a lot. Thanks,

[david s]

Re: Why does bottom of my bread loaves burn?

Fire bricks do not contain aluminium. It is in the form of aluminium oxide or more commonly known as alumina. It is not the alumina content that makes the brick denser, that just makes the material more refractory. High duty fire bricks do contain more alumina than low duty and are usually denser than low or medium duty, but not always. In the case of an insulating firebrick that has been designed as a hot face brick, it has a high alumina content but is extremely light. The high duty fire brick is more conductive because it is usually denser, not because it contains any metal, attaining its density mostly via a greater degree of vitrification, increased shrinkage and reduced porosity,usually obtained by being fired to a higher temperature.

[banhxeo76]

Re: Why does bottom of my bread loaves burn?

What kind of firebrick did you use for your cooking floor? Standard or Medium Duty fire brick? Standard firebrick usually has aluminum content around 20-27% which prefect for bread baking. Meduim duty firebrick has aluminum content at 35-40% which is prefect for pizza or flatbread (or any thin bread). Firebrick with higher aluminum tends be more conductive since there is more metal, therefore, transfers heat to bread or pizza at a faster rate. Since bread usually has more mass and it takes a lot longer to cook than pizza, higher aluminum firebrick usually cause the bottom of the bread to burn before the bread is completely done. Firebrick with aluminum between the range of 17% and 25% would be perfect for bread and it is also would work for pizza as well but meduim duty should give pizza a better result. You may use medium duty brick to bake bread as well by cooking at a lower tempeture but the result won't be as good as a low duty firebrick. French bakers in France use firebrick that have aluminum content as low as 15%. However, those brick are not strong and have shorter life span. Therefore, they simply replace those floor bricks whenever they need to. That is why I think French make better bread and the Italian make better pizza because their WFO designed for different purpose.

[Pdiff]

Re: Why does bottom of my bread loaves burn?

I have a standard FB plans Pompeii 48" with probably 1-2" of refrac mortar, 3 layers of the FB blanket, insulation and housing around the dome. The floor sits on 5-6" of vermiculcrete which is on 6" of concrete.

I like the profile idea. I'll need to try that.

[texassourdough]

Re: Why does bottom of my bread loaves burn?

Hi Mike, My oven is a Casa 100 refractory with 1 inch of extra refractory to give extra mass so it is about 2 1/2 to 3 inches thick. While I can have it ready to do pizza in 45 minutes it is NOT ready to bake for at least 1 1/2 hours total (another 45 minutes) plus an hour or so of heat soaking. And, at that point it cools much faster than if I burn for another hour. With the extra burn the temp drop off is much slower indicating that the refractory is not stealing energy from the oven - when I do this I often end up leaving the door open a while to cool it off if my loaves are proofing faster than the oven cools.

A straight Casa might be ready in 2 hours or so from my experience. I can't extrapolate to a Pompeii. But barrel vault bakers routinely heat for at least three hours or more in my experience.

[GianniFocaccia]

Re: Why does bottom of my bread loaves burn?

a thicker walled, barrel style which has a much larger thermal mass

Hey Mike,

Good to hear from you. How's the oven working? Are you able to use it much in the winter?

I think most of the barrel vaults are built with 4.5" walls and ceilings, same a pompeii like yours, but takes more fuel to heat up because of the vertical corners. I think you'll need to ask one of the builders here who have one of each. Bob maybe? (AZPizzanut)

John

[SableSprings]

Re: Why does bottom of my bread loaves burn?

My oven's a slightly modified Pompeii (a bit of a teardrop shape - see Dome Build in the photo album link below my signature). The internal width is 39" and the depth is 45" (from door stop to back). I've been baking primarily bread in it since December of 2009 (+1,200 loaves to date).

I've posted this a couple times, but I think it's important for everyone that wants to bake (other than pizza) do some temperature profiles over time to really see the heat loading and thermal properties of their oven - Pompeii or Barrel. Until I actually graphed several firings and their temp profiles, I really didn't have a good understanding of how best to use my particular oven's heating character.

The baguette below was baked at 580?F (hearth temp) for 18 minutes. I got excellent spring, just a bit of "extra carmelization" on the bottom, and great crumb. I've included one of my earlier temp profile graphs as well.

[brickie in oz]

Re: Why does bottom of my bread loaves burn?

, barrel style which has a much larger thermal mass.

Not all barrels have masses of mass.

[mfiore]

Re: Why does bottom of my bread loaves burn?

Quick question pertaining to this great discussion. What type of oven is everyone using? I would assume the dome style pompeii oven would take less time to saturate than a thicker walled, barrel style which has a much larger thermal mass.

Before interpreting heat times, etc, I want to be sure everyone is talking about the same thing.

[Pdiff]

Re: Why does bottom of my bread loaves burn?

I don't usually pulse fire. It takes a lot of wood. With a shorter, one time fire (2-3 hrs), it cools quickly. Also, by "cooking temps", I mean further meals, etc, not bread. When I do it, I progress down to slower and slower cooking things, finally ending up with drying of fruits or jerky.

I often do cool with the door off too. Yes, the floor is definitely hotter that the dome, too.

[texassourdough]

Re: Why does bottom of my bread loaves burn?

Wow! Bill! I envy your insulation! WOW! Your big challenge is undoubtedly getting the oven cooled down to baking temps. (It cools pretty fast with the door open but... that that invites problems too). Yeah, brown rice flour will help if your hearth is too hot but...the goal is to have it the right temp!

I would almost bet your hearth is warmer than the dome when you bake - i.e. your hearth mass and insulation may be more efficient than the dome. It is my impression that most ovens have domes at baking conditions that are 20 to 40 F warmer than the hearth (after equalizing). Have you checked yours?

The reason that pulsing works so well is that the preliminary fires warm the deep refractory. As a result it doesn't "drag down" the temp of the surface by sucking heat out of the oven as much.

Thanks!
Jay

[Pdiff]

Re: Why does bottom of my bread loaves burn?

You all are firing longer and loading hotter than I typically do. I need to try those. Pulsing, like Mike suggests through multiple fires really heat loads the oven too. I was skeptical about that until I tried it and had my oven stay cooking hot for almost a week.

Outside of firing technique, I've had good luck using brown rice flour under the loaves to prevent burning. I think you told me about that, Jay. I'd also agree with not moving the loaves around.

Bill

[texassourdough]

Re: Why does bottom of my bread loaves burn?

Hi Mike!

You are definitely right about the dough cooling the hearth. I have not seen credible numbers but when you put wet dough at 80 F on hot hearth at say 500 F the dough will both cool and emit steam that will cool the hearth surface to the 212 range. Now, the temp 1/4 inch below will be 500 or so initially (assuming good insulation and loading) and that heat (and deeper) is what flows to the surface to cook the bread. (I know you know that but this is to be more complete for other readers!) When you pull the bread from the oven the hearth will probably be no hotter than 300 to 325.

I am always amazed by the low temp at which many FB people load. I usually load at 565 F on the hearth but my loaves are 1.5 to 2 lb boules and they need a bit more time (so a cooler oven). Your time of 18 -20 minuted for baguettes at 580 or so makes good sense. This spring I need to do a baguette bake. Since I spent a week at SFBI on baguettes I make them great indoors but I have to make them SHORT and it would be wonderful to make some LONG baguettes! Yes! Gotta do that!

Good comments! (Good to know you are in Roseburg. I may have to look you up next time I am in Oregon for steelhead - like this fall!)

Bake On!
Jay