Time to build my bread / pizza oven

[matthewcove]

Re: Time to build my bread / pizza oven

Finally got to test the oven on my regular sourdough bake. Lots of work still to do on the oven, some refinements to do around the door area. Here is a picture from this morning bake, there are more on my blog here.





Matthew

[matthewcove]

Re: Time to build my bread / pizza oven

Today I have been experimenting with improving the air flow for firing the oven with the addition of a firing door. This aims to optimise the door shape while burning wood in the oven.

Full discussion of why and how on my blog here.



thanks

Matthew

[david s]

Re: Time to build my bread / pizza oven

Today I have been experimenting with improving the air flow for firing the oven with the addition of a firing door. This aims to optimise the door shape while burning wood in the oven.

Full discussion of why and how on my blog here.



thanks

Matthew

The higher the temperature the greater the heat loss. This means that the temperature rise when starting the fire needs to be quite gentle or damage to the refractory can result. At the lower range of our firings (ambient to 300 C) it is important not to increase the rate of temperature rise too quickly because uneven expansion takes place and damage to refractory (bricks, mortar or castable) can be too much for the materials to withstand. It doesn't matter how good the quality of your refractory is, damage can still occur. At the higher end of our firings (500- 650 C) for surface temperatures at least there is also considerable increase in some materials expansion rates so this is also a danger zone. Using what some on this forum call a "blast door", or forced air induction with a fan or blower, to achieve a hotter fire is the equivalent of turning a kiln burner on full from start up. Not only does this damage the wares in the kiln, but can also damage the refractory. For these reasons I think a blast door is better left off if you want to be kind to your refractory.

[matthewcove]

Re: Time to build my bread / pizza oven

I'm no planning to force air into the oven, the firing door is designed prevent flames from coming out the door as this oven has a proportionally bigger door than is optimal for this design of oven. My firings have been on the hot side with the full door and I am looking for ways to keep the firing temperature down. What other things can I do to keep the temp down. reduce air flow, type of wood, size of wood?

thanks

Matthew

[Greenman]

Re: Time to build my bread / pizza oven

It is all about control Matthew. If your damper, however you configure that, allows you to slow the combustion process to the pace you want then you have nailed it. I use the blast door to get it started properly, not for long, and once it is all cranking I use the heavy insulated door to restrict the airflow and how you set that can mean either a very slow fire or something a bit more active.

Dave is right about rapid heating and slow and steady burns about the same amount of wood to achieve the same temps, it just takes a little longer. Nothing that starting a little earlier won't fix.

[david s]

Re: Time to build my bread / pizza oven

If you want to get the temperature down either don't fire up for as long or just wait until the temperature drops. If I'm only cooking a few loaves of bread in my small oven, then I fire for only one hour, which is sufficient to cook the bread, although the temp drops off faster because the heat is still penetrating the outer layer of the refractory. The advantage here is that I don't have to wait for the temperature to drop off. If I were to do a second load of bread then I would fire it up hot and wait for the temp to drop by which time the heat will have soaked through the whole oven and it holds it heat for longer.

[matthewcove]

Re: Time to build my bread / pizza oven

I have a 6" flue with a stack height of more than 2m. This is generating a lot of draw. I will try balancing the flow next time with the flue damper and the insulated door just propped open a little to see if I can get a much slower burn. I'm not worried about how long it takes to fir as I do that the day before baking anyway.

thanks

Matthew

[matthewcove]

Re: Time to build my bread / pizza oven

Hi David,

the final temp in the oven is about right, its the temperature during firing that is too high, but it sounds like I need to control my air flow rate better. Currently I'm only doing one or two bakes, but planning on doing 4 or five each firing so i am firing the night before as practice even though it's not really needed now.

Just off outside to put my first attempt at baguettes in the oven. Exciting times.

Matthew

[david s]

Re: Time to build my bread / pizza oven

Matthew,

How are you measuring your oven temperature? Is it with an IR gun, thermocouples or an air temperature thermometer inside the oven?

[matthewcove]

Re: Time to build my bread / pizza oven

I have one thermocouple buried in the hearth near the hearth / insulation boundary and I use an IR gun to measure the surface temp inside the oven.

[david s]

Re: Time to build my bread / pizza oven

The reason I asked is that an IR gun will give you a pretty false idea of oven temperature if taken during or just after firing up because it is reading the surface temperature and will read way higher than your thermocouple. They are quite useful once the oven has adjusted itself and the temperature evened out after firing. You will have no doubt found this out when comparing readings from both sources.
You must be doing something right because those loaves look great.Keep cooking.

[matthewcove]

Re: Time to build my bread / pizza oven

After firing the oven for 3 hours the temperature deep in the hearth has only risen to 59 C, once it starts to rise it initially rises quite fast, until is peaks at around 270 C. it then equilaterals over night to around 265 with the interior surface a little lower at around 260, which is the temp i want for starting with focaccia and small baguettes etc. At some point i will do some plotting of temperature curves so that i can build a thermal model of the oven so i can feed in the current temp measurements and calculate the approximate burn and wrest required to get to a desired baking temperature.

Matthew

[matthewcove]

Re: Time to build my bread / pizza oven

The oven is still not finished, it still needs a roof. I will eventually get chance to make some more progress, but for now my job is taking up too much time. The little time I have has been spent trying to improving the quality of a couple of bread recipes. The results I am getting are certainly far better than what I have managed to achieve with a domestic oven. I have a long way to go to get my results consistent, but I am slowly learning how to fire the oven to the right temperature and to deal with changes to fermentation as the weather and temperature change.





Matthew