Homebrew barrel oven on metal stand

[Petter]

I got the hands on a metal stand that begged to be transformed into an oven... So be it! Started the build on the 24th of mars. Still sub zero degrees in the night, can't work on the big oven anyway...

Bottom 60x100 cm wide x long, 7 cm deep. Look at the bottom right in the picture for understanding.
- Supported 3 mm hot rolled steel.
- Insulation made of 7 cm mixed leftover CaSi- board and ratio 25:1 perlite:cement (by volume, 2:1 by weight). About 30 % board and the rest perlcrete.
- 1-2 cm Homebrew for leveling and floor and dome support.
The homebrew was cast inside this frame on the insulation.

No stainless needles or PP burn out fibers were used in the homebrew. The sand was plain sand, 0.1-1 mm in size. The clay was kaolin, I did not have fire clay. It is less stickey but more refractory and shrink less than regular fire clay.


Dome
- 3 cm thick front and back.
- 3 cm thick sides, gradually thicker to 5 cm at the dome top. I did not fill in the casting defects after mold removal.
- 27 cm high, 40 cm wide and 70 cm deep.


Flue gallery
- 1:5 refractory cement (Calcium Aluminate) and perlite. About 3 cm thick adjacent the dome and 5 cm towards the front. I was scared of spalling if OPC was used and I already had the CA.
- About 50x150 mm flue, XX cm high.
- 15 cm opening height (9/16 ratio, 0.56 instread of the commonly 0.63). XX cm deep.
- The opening was cast on a half bucket and expands towards the opening from the oven chamber.
- Thin render with homebrew. Maybe 2-4 mm to protect the perlcrete.


Insulation
- 7 cm on the sides expanding to 10 cm around the dome of 25:1 perlite : cement (portland). 2:1 by weight. 0-5 mm perlite fraktion. About 0.22 kg/l dry density.
- 7 cm on the back.

Final render
- Galvanized wire mesh 2x2 cm squares around the whole oven.
- 1.5 cm 4:1:1 sand cement lime.
- White Silicate paint.


Curing
I'm lazy so I got an electric bbq fork lighter 500 W and inserted it into the oven after a week of wet curing under cling film. Everything but the paint was finished by then. Let the handle stick out and sealed the front and back opening with insulating firebricks.

First 48 h was on-off with 30 min interval using a timer. Too much steem otherwise. Next 12 days were constant 500 W. The back wall temperature slowly rised 10-15 C per day to top at 180 C after total 14 days. Constant temperature the last few days. The garage windows stopped beeing steemy in the mornings after 11 days. Barely any water adsorbed on cling film on for 2 h after 14 days. Time for fire!

I got help from 3 hungry neighbours to lift the oven into position and started the fire the next day (today actually). 200-300 C top dome temperature for 8 h. No steem, cracks or so. Increased to 500-600 C over next period of 4 h. Everything went very well. Two small hairline cracks on the inside of the opening where the 2 mm homebrew layer was. I have not noted anything else. Not in the dome or on the outside. Very pleased with that so far.


Lovely weather today!


Curing continues tomorrow. Pizza on monday!

Thanks a lot to everyone who contribute to this fantastic forum and knowledge sharing! I would not have done it without you.

[david s]

That's a very interesting build. A 3cm thick homebrew casting is pushing the boundary. I assume you were trying to reduce weight as much as possible. What is the total weight? The insulating castable for the gallery reduces the thermal mass and conductivity where you don't want it but you pay the price of reduced strength. Coating it with dense homebrew should protect it from bumps and abrasions.
The addition of polypropylene burnout fibres to the dense homebrew castable would give you a measure of steam spalling protection. You're lucky it didn't crack, you've done a good job of slow drying.
Where's the flue?

[Petter]

Thanks :-)

I like to push limits and the size was determined by the work-bench. Restrictions force creativity.

In width, I had leftover Biscotti bricks which were 38 cm wide if 3 were put next to each other and I wanted to use them. I also wanted the insulation to be twice the mass thickness for weight (yes, to be carried to position) and fuel. I also wanted as much insulation as possible. 38 + 1 + 2*3 +2*7 was about 60 cm in width. 1 cm expansion gap. I would estimate (based on the sounds my neighbors were doing...) to 200-250 kg. The stand is estimated to about 30 kg.

I agree, the gallery was a compromise. I wanted to have as much depth in the oven as possible for even heat and ~20 cm in the back for the fire. If the pizza comes to close to the opening, it does not cook enough to be turned when the fire-side wants to. Since it is has straight sides in the back and front, the layers of mass, insulation and flue add up in depth. I also did not want the flue to go on the other side of the homebrew. I wanted insulation between. Hence the 5:1-cast. After another whole day´s fire, the temperature is 500-600 C inside and 30-40 C on the outside. The rear is the warmest with points up to 50 C. The insulation at the top is 3-4 cm thicker that near the bottom, but since heat rises, the outside temperature of the oven is very similar all around. I do regret I did not put an extra 3 cm perlcrete in the back, but I was keen on inside depth. It is the hottest place due to the fire location. However, it could have been worse. I can hold my hand there for quite some time without burning, but eventually it gets warm.

After doing this, I would never go below 10 cm insulation anywhere on a oven that was not restricted in size. Just not worth the compromise.

Funny you mention it, I did coat the gallery with 2-4 mm homebrew for bumps and such. This morning I could se one crack on each side of the gallery section between the front dome mass and CA-perlite cast. It was like when the dome contracted as the temperature dropped, a gap formed in-between. It starts at the bottom and ends where the flue starts on both sides. Does not worry me since the gallery can't go anywhere. I'm glad nothing else has happened. Maybe it is because the 25:1 mix is fragile enough to get squashed when the mass expands instead of breaking the outer render.

I skipped the bur out fibers since I thought that a careful drying would be sufficient. I don't think I would have succeeded equally well to dry it using fire as only heat source. The dome is too low and it was difficult enough to keep the temperature in the 200-300 C range, even with a small fire.

The flue is only the part in the gallery, so about 20-25 cm high. The last oven (similar shape) looked like a church and I like the neat look of this oven. So far, it draws sufficient. Especially with a draft door (IFB). It keeps the flames long and slow due to the air deficit. The front is still clean after 2 days fire. Most smoke comes when a log is added, even if is pre-heated in the gallery. During these moments, smoke comes out the front. Otherwise, it burns very clean with no visible smoke. I will determine tomorrow while cooking if I should add height to the chimney or not.

[david s]

I agree about pushing the limits, I do too. It’s fun seeing what you can get away with. Can only try I and see how it goes. The elimination of a flue pipe does away with complications of pipe expansion and sealing around the pipe. With no flue cap I presume you cover it to keep out the rain. The flues purpose is just to get the smoke away from your face during operation and the extra height of the insulation on the top does that job.
I would expect the very thin 2-4mm homebrew coating over the insulating castable of the flue gallery to be subject to cracking and flaking, but time will tell and you can always reapply some more.
Keep us updated on its performance. I bet you’re already planning the next one.

[Petter]

Ha ha, yes, I forgot to take the homebrew smear thickness into acount when casting the gallery... I did not want to infear the over all mouth shape too much, so I just smeard some.

It will be covered with a small removable roof. A gas-bbq rain cover would fit perfect, but I want to be able to see the oven from the garden even when not in use.

Very exited about today. Rain is still falling. Hope it stops Pizza for lunch. I'll let you know!

The next oven is under the tarp... The garden and kids have priority but I'll build some when warmer, better weather comes.

[Petter]

Pizza today. The rain stopped. 3 h preheat. Mostly 480-520 C (900-970 F) on the floor. Pizzas baked for 32-52 seconds. Best was about 45-52 s. 35 was good but 32 gott bitter in the bottom. Temperature was 560-570 C for that one. None was burned. They all looked pretty similar.

24h, 2% sourdogh. 12+12, 23 C, 65 % hydration. Low activity unfortunately. Only 10% rise. Made the crust low and dense. I have a few fails with white SD. Will go back to yeast for a while now.

47 s pizza:



The comment from middle child:


oven front after 2 h fire and cooking without a draft door. Not too bad. I'll skip the additional height on the chimeny for now.


Thanks for reading :-)

[Petter]

14+10 h RT dough. Hand mix, 4 stretch & folds. 0.15 g yeast per kg flour. 65 % hydration. Ramlösa kvarn 00 flour. (Swedish 00-flour)

65 - 70 s bake time. 430-520 C deck temperature. Rotated after 20-25 s.

Made 4 Margherita, 2 salami and 2 with only EVOO, rosemary, garlic and sea salt. 320 g balls, 12" pies.

Like the more even browning better but miss the rich favour of the sourdogh. Hmmm...


Upskirt:




next deleted image. Edit: posted the same pizza twice :-) (embaressed) I deleted the correct top image unfortunately. The upskirt image us correct though. Sorry...

[sergetania]

Nice looking pies!

The top of the yeast pizza looks very different from sourdough. Maybe something else is going on contributing to the flavor difference between commercial yeast vs sour/wild yeast . Do you always have flame across the dome ceiling when baking a pizza? Has the dough temp reached room temp for the sourdough before going into the oven? Sometimes cold dough results in excessive leoparding. That could also explain low rise. Could be the other way around, the sourdough just has not risen enough. Honestly, I never had much luck with pure sourdough pizza. Even when baking bread, I prefer 50/50 yeast/sourdough starter. For pizza, 24+h yeast dough usually develops plenty of flavor so I don't miss sourdough.

[Petter]

Thanks :-) It is fascination that fermentation can make such a difference. I asked the two oldest kids, 5 & 8 years old, and they both said the first (SD) pizza was the best. More favour in the crust. Hmmm better to learn to please the croud... I will try your suggestion of adding yeast to the SD. Sounds like a good compromise.

I've learnd that the leoparding comes from sugar deficit in the dough. That's why you get a pale crust with dark blisters. I personally strive for the second-pizza-look, a even browning. It taste sweeter and more complex but lack depth. Only wish to combine it with the SD-fermentation taste.

Yes, I always have a flame while cooking. The top takes too long otherwise. Room temperature dough as well. My spy indicated a 10 % rise. People at Pizzamaking.com seems to bake at 50-80 % rise. That would take me 48-72 h at room temperature with 2 % starter. Got to adjust the feeding schedule and starter amout. So far I've taken my bread-SD, given it a few feedings with 00-flour and then used it. However, it has never exceeded 100 % rise. Even without salt.

I'm not the best with bread but can make decent loafs with sufficient consistancy. So I got the confidence just not really know how to do the error-ellimimation process. The salt addition really slows down the fermentation, so in bread, I add it after 45 min. It works well. Maybe try that for pizza too for a start.

[sergetania]

2% starter is really not enough (speaking based on my bread baking experience only). Basically, the idea is to increase the starter until it takes only 24h or even 12h, whatever fits your schedule. There's nothing wrong with 10-20% of starter. That's where the taste comes from. In order to avoid sour taste, use young starter before it starts to smell sour (8-12h, just when it's peaking).

When I bake bread I make a quick poolish with yeast and then use that and young starter, 50/50. This helps with consistency and the taste is very good.

[Petter]

Thanks, I agree, I followed the chart in Ville and Besmirs' book (owners of Lilla Napoli) and it was quite hot that day, hence the low addition. Will increase until next time and also start with room temperature water. I'll try 6 %, then 12 to dial in my culture.

I usually use 20 % with bread and 6-7 h fermentation at 24-25 C dough temperature before regarding in the frige for reference.

[Petter]

Today's bake. 6 % starter, RT water, dough temperature about 24 C. 11+10 h. 64% hydration.

Dough has risen 10 % after 11 h. 50 % rise when baked. Got nice crust this time. 61 s bake at 480-520 C deck temperature. The dough was smoother but not as relaxed as I wanted compared to yeast. I think I'll aim for something like 1.7 rise.

Fire...




I loaded a bit too much tomat sause and teared 3 bottoms...You don't get to see those ha ha.! The other five was okay. Here is 1.5:

61 s



/Petter