Why does bottom of my bread loaves burn?

[texassourdough]

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.

[Pdiff]

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.

[banhxeo76]

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.

[david s]

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.

[poweredbypizzas]

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,

[SableSprings]

Originally Posted by poweredbypizzas

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.

[Spunkoid]

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.