Driving heat across the cooking floor

[Mike from Ottawa]

Re: Driving heat across the cooking floor

great post. just finished my oven - Dome Style. did the test fires. Pizza this weekend. oven was approx 750degrees, put pizza in 2min 40sec and done. bottom was not brown every thing else was. nice char around the edges. turn the za two times. so i guess I should wait and keep putting the wood to the oven to get the base hot?
How do I add pics to my posts?

[texassourdough]

Re: Driving heat across the cooking floor

Hi John!

Probably a good idea.... It will let you bake/cook with a slightly lower hearth temp for it is supposed to have a higher heat conductivity (which means it can send heat to the surface faster and thus more easily burn but it also means it could cool faster.... Don't know the heat capacity for soapstone vs. refractory - but then it is over refractory so???)

On pizza you may want to have the hearth just a hair cooler. Four seconds on the semolina test might be right???

Good Luck!
Jay

[GianniFocaccia]

Re: Driving heat across the cooking floor

The other issue would be that it would be hard to be consistent partially loading the oven and that would make the whole process more variable

Jay,

Great explanation!

Given the fact that I have way more knowledge and experience yet to acquire (with both bread dough and my oven), the simplest approach is to fully saturate the oven, time the final rise to coordinate with the oven equalization, and viola! Testing may begin! Oh drat! I forgot - I have a soapstone floor that's supposed to burn bread bottoms! Hmmm... parchment?
John

[texassourdough]

Re: Driving heat across the cooking floor

There is no real need to fully saturate most ovens for a single batch but it will affect the temperature cooling profile and that will impact the bake. Not necessarily negatively - depends on the bread being baked and how hard the oven was heated.

Let's take a hypothetical situation. Let's say you have perfect insulation and you heat the inside of your oven to 900 degrees and the outside of the refractory is just warming to 100. For simplicity lets assume the heat profile through the refractory is linear so that in the center it is 500 degrees (half way between). If we close up the oven the heat will spread out so the whole refractory is 500. When we load the oven we will drop the temp in the oven to about 350 (my guess) The hearth surface may actually cool to near 100 or so - well below water boiling. The heat that makes the temp 500 in the refractory will then flow back to the oven to bring the temp back up to 450 or so during the bake - to give you a pretty crust.

Note: we started with a NONSATURATED oven. Normally the oven is pushed long enough that the refractory is more loaded than my example and that is important for the insulation isn't perfect - at least not very close in mine. The trick I think in partially loading the oven is that it will be "cooling" through the entire bake at an accelerated rate. So we probably need to load at a higher temp and bake a bit longer (maybe a lot). The other issue would be that it would be hard to be consistent partially loading the oven and that would make the whole process more variable. In the end it may come down to what your expectations are for your bread. If it is too variable for your taste you will probably shift to longer heat loading... But...every oven is different so...

Good question!
Jay

[GianniFocaccia]

Re: Driving heat across the cooking floor

I totally agree Jay, but if I plan on only cooking two loaves of bread or a roast there is no need to heat saturate the oven and then let the temp drop

I totally agree with Jay's explanation of temperature vs heat and the analogy using water. One can cook a batch of pasta in a small volume of boiling water but it is generally agreed that the same pasta will cook to a better consistency in a large volume of boiling water. Just like heat-loading a WFO, it takes more energy to heat a large volume of boiling water than a small one. Jay, do you think a heat-saturated oven might behave in the same way? I would be tempted to cook a batch of bread like David in a partially-loaded oven if I wasn't planning on using it for the next few days.

John

[texassourdough]

Re: Driving heat across the cooking floor

Hi David! As you know, it is all part of "knowing" your oven! Sounds like you are doing a real short circuit of normal WFO practice, but...there are SO many variables that there are lots of odd combinations that work well for various purposes if you can find them!

[david s]

Re: Driving heat across the cooking floor

I totally agree Jay, but if I plan on only cooking two loaves of bread or a roast there is no need to heat saturate the oven and then let the temp drop. Why use up way more energy and time than you require. My oven in this case has usually only just gone white at the top half of the dome, nowhere near "saturation". If planning on cooking lots of bread or a large party of folk for pizza the regime is quite different and that's when you want plenty of stored heat in the oven.

[texassourdough]

Re: Driving heat across the cooking floor

I haven't been following this thread but I think some recent comments deserve some qualification...for the definition of "saturated" that has been used is IMO misleading.

The normal definition of "saturated" would imply that the oven cannot store any more heat.

Having the oven go "white' does NOT mean the oven is saturated by any means. It means the surface is at 750 or so but doesn't tell you what the temp is at the far boundary of the refractory. For those with relatively thin, well insulated ovens the oven may well be approaching saturated but for those with heavier ovens the oven may be 2 or 3 hours or more from being even reasonably "heat saturated".

Barrel Vault ovens routinely heat for 3 to 4 hours before being used for bread baking and they will clear in an hour or so but are NOT heat saturated even at 4 hours. They need an hour or more to equalize and have the temps become more uniform through the refractory so that the stored heat will be available to reheat the oven as it cools from cooking/baking.

There is also a tendency in this list for people to confuse temperature with heat. Temperature is like pressure - it can be measured at a point. Temperature and pressure are properties and do not flow - though they do make things (like heat) flow. A match burns at about the same temp as a piece of wood. They have the "same" temp but they do not produce the same amount of heat. Heat is like water - it has a presence and can flow and be stored (in materials). A teaspoon of boiling water has the same temp as a gallon of boiling water but they contain differing amounts of heat. One has enough heat to cook something with the heat it contains the other does not. A just cleared WFO is much the same - it may be hot but it won't contain as much energy (stored heat) as it can.

Crawling off my stump and dodging the fruit and tomatoes!
Jay

[Sharpshooter]

Re: Driving heat across the cooking floor

Great information, thanks. I ran into heat management issues on my first cook in my new oven. I didn't have a large enough fire going while cooking, so the floor temp dropped considerably. Next weekend I will try again, with a good fire going while cooking.

[david s]

Re: Driving heat across the cooking floor

"When the oven goes white, you absolutely know the brick is saturated with heat. I never cook a thing until that event occurs."

I guess we all do it a little differently. I often cook in my oven well before it goes white. If I'm doing a roast or bread I usually give the oven one hour of flame (this is where I use my stopwatch) which is usually enough for the top of the dome to begin going white and the rest still black. It is then enough to do the cooking. Faster that way and uses way less fuel. Using this method it's easy to cook a roast after work during the week. If I'm doing pizza for quite a crowd then I let my oven go completely white and about another 20 mins of flame before preparing the floor.If it's just for the family and we only want 3 or 4 pizzas I'll skip the extra 20 mins.

[david lyons]

Re: Driving heat across the cooking floor

Thanks all for the comments.

I take the point re "what is the point?", My thinking is that it is easy to make provision now and bloody hard later. Also I have a thermocouple I bought some time ago and I have to justify it don't I?

I'll go with the tube midway up and against the dome.

Dave Ly.

[Les]

Re: Driving heat across the cooking floor

I could see the benefit of a thermocouple placed near the outside of the dome brick to indicate when the dome mass has been thoroughly saturated.

Gianni / David - I totally agree with you. But, When the oven goes white, you absolutely know the brick is saturated with heat. I never cook a thing until that event occurs. Then it's just a matter of letting things cool down and adjust to the temp you need. I'm not making a point for or against the toy's, it just never penciled out for me.

Brick - we seem to be on the same page

[david s]

Re: Driving heat across the cooking floor

with my oven I tell this by the slight warmth that makes its way down to the base of the dome. When this warmth has reached the base the oven is heat saturated and ready for pizza. A hand held to the outside can tell you lots.This method may not apply to those who have really well insulated ovens. If your oven is hot to the hand on the outside your insulation is damp.

[GianniFocaccia]

Re: Driving heat across the cooking floor

Until I learn my oven I'm going wih the laser as well, but...

I could see the benefit of a thermocouple placed near the outside of the dome brick to indicate when the dome mass has been thoroughly saturated. With experience this should become intuitive but I'm sure thousands of ancient Italian housewives learned this without the convenience of a digital readout.
John

[david s]

Re: Driving heat across the cooking floor

People who are new to wood fired ovens always seem to be rather obsessed with reading temperature. After lots of firings your stopwatch hand and eye are enough. I always use the semolina on the floor trick (3 secs to turn black) to test floor temp. An infrared thermometer only reads the temp of the surface, so it has some limitations.