A friend gave me a stainless steel beer keg a few years ago. It's been sitting around outside not doing much of anything. I've always wanted an oven hot enough to make Neapolitan style pizza at home but it takes up so much room to have a dedicated wood fired pizza oven.
In doing some research on how to cook pizzas at home I came across the Roccbox and Unni pizza ovens (look them up, very cool units). They are small portable units that get super hot and allow you to cook a pizza in a few minutes... They are also super expensive. I thought that I could build something similar at home and it would make a good challenging project.
In terms of this project being challenging, I got my money's worth. The whole build took me well over a year before I landed on a design that worked to the point where I was happy and I could cook a pizza in minutes. I went through a few design changes and iterations before the final design that I am sharing with you here. I have a video of the whole build process, it's a good watch if you are interested in seeing some of the design changes as I build it.
For a proper wood fired pizza oven to achieve 1-2 minute cook times needed to cook a Neapolitan style pizza, the oven would need to be able to have a dome and floor temperature of at least 800F. Optimally more like 1000F dome temperature. This oven gets hot!
Step 1: Parts and Tools
The following is most of the parts used to build the oven but there could be some parts I missed.
Parts for Body and Frame of Oven:
- Stainless steel beer keg
- 1" angle stainless steel
- 1" stainless steel flat stock
- 18 gauge stainless steel sheet metal
- 1/4" mild steel plate
- Refractory cement
- 1/4" stainless steel rod
- 3/32 stainless bolts
Parts for Propane Burners:
- 2.5" schedule 40 pipe
- 1/2" threaded steel pipe (NPT)
- 1/2" NPT pipe fittings
- 1/2" gas rated ball valve
- High flow propane BBQ regulator and hose
- 1" stainless steel tubing
- 1/4" brass pipe and fittings (NPT)
- 1/4" gas rated ball valve
- Thread sealant or PTFE tape
- Stick Welder with stainless steel welding rods or MIG welder set up for stainless welding
- Angle grinder with cut off disc and flap disc
- Drill and drill bits
- Hand tools
Step 2: Video
Here is a complete build video from start to finish. Includes all my iterations and changes. The written build are in the following steps.
Step 3: Building the Oven Body
The beer keg has a few good things going for it: stainless steel, so it's durable and corrosion resistant, a round cylinder shape, that will make a good outer shell of oven and the shape and size would should allow for cooking personal size pizzas. My idea was to line the inside of the keg with refractory cement that will act as thermal mass and have it wood fired with a rocket stove (more on this later). The thermal mass of the cement would allow the oven to retain heat and maintain an even cooking temperature.
So first thing I did was cut the beer keg in half lengthwise using an angle grinder and cut off disc. The ends were also cut off, one end was for the opening and other end I welded shut again using the opposite end of the keg. You'll see why in the pictures as the ends of the keg has a lip.
Since the inside of the keg is smooth, I wanted to make sure there would be lots of surface area for the refractory cement to stick. I bent up some stainless steel sheet metal strips into a zig zag pattern and then welding them all inside of the keg, this kinda acts like rebar in construction. I hind sight this was probably not necessary as the cement once set was super solid and in the shape of an arch.
The refractory cement I used is meant for high heat applications, I picked it up on Amazon but I also found it for sale at a local brick supplier. The cement mixes and works just like regular cement, I just followed the instructions.
I needed a few buckets of the refractory cement, I mixed up a batch and lined one side, then let it set before doing the opposite side. The cement had a tendency to slide on a round surface like the keg so I had to do it this way in sections. Once set the cement it's super hard and the body is very heavy, giving lots of thermal mass.
A thermometer was installed on the side of the keg by drilling a hole through the side of the keg and then using a masonry bit through the cement.
*Note do not use regular cement or mortar to line the keg, it will not hold up under high heat conditions. Also when working with the refractory cement, do it in a ventilated area with a respirator as the cement contains silica and it's not good for your lungs..
Step 4: Building the Frame
For the frame of the oven, I decided on a simple square frame made from 1" angle stainless steel stock. I first welded together two sides and made sure they were square by measuring on the diagonal to make sure they matched in measurements. Then welded the two sides together using some more 1" angle stainless steel.
For the height I just determined what would be comfortable for me to slide pizzas in and out of the oven. The width was determined by the size of the beer keg as the open part of the keg would sit on top of the frame.
Casters were installed so the whole oven could be moved around easily as when finished the oven has some heft to it.
The deck of the oven had a mount built so I could bolt a burner directly to the floor of the oven, this made the burner removable. This took a few iterations and you will see in the following few steps how this was done.
Step 5: Info: Powering the Oven and 1st Design
The deck of the frame is where the beer keg would be mounted. Initially I had tried to power the oven with a wood fired rocket stove. I thought that using wood would be the ultimate way to cook pizzas, just like a proper wood fired oven but I quickly realized that while it does work. It takes a lot of fuel and time to get the oven up to cooking temperature with a wood burner. I was able to do it, but it took 30 to 45 minutes to get up to a proper cooking temperature in the 800 to 1000 F range. It could be my design as well but after a few iterations I abandoned my wood fired dreams and switched to propane. I have included a few pics of the wood burner.
You can see how the wood burner in another Instructable and video.
Traditionally the floor of the oven is some type of stone, but the issue with this was it was hard for me to fine a stone thick and large enough without the cost being crazy expensive. I landed on using 1/4" mild steel plate and heating the floor to achieve a nice hot floor temperature that would allow me to finely control the temperature. Kinda like a baking steel instead of a baking stone.
So the final design was to heat the floor and power the inside of the oven with a propane jet burner. The propane jet burner is of my own design and used it for a previous project and I have an Instructable for that as well. The mounting location is at the rear of the oven, the size of the keg leaves enough room to cook a personal size pizza. See the next step.
Step 6: Main Jet Burner
******Warning building a burner like this is dangerous, if you don't have a clue on how to safely work with propane do not attempt this. I take no responsibility if you injure or hurt yourself or others or set anything on fire.******
Now that that is out of the way.
So the main burner of the oven is a jet burner. It's one of the simplest burners to make, it's really just a controlled stream of propane lit on fire. I did a previous Instructable that you can see how to build it, it was used in a wok station https://www.instructables.com/id/Homemade-Outdoor-...
Although I did make a few small modifications to the burner in the original design I used a high pressure regulator, in this design I didn't need as much pressure so I went with a regular high flow BBQ regulator. The difference between a high pressure regulator (red in color) and a low pressure is the high is 1 PSI+ where as the low is less than 1 PSI.
Also the orifice hole was enlarged, to 5/16". This achieves two things, it allows for the flame to be less focused and also less intense. I wanted a much less intense flame than what was used for the wok station burner as I wanted to spread out the heat and flame inside the oven. Don't get me wrong the flame is still crazy hot just not as intense.
The burner was then mounted in the same way as the wood fired burner and bolted onto the floor of the oven.
To the main jet burner, the floor burners were plumbed into it as well, more on that in the next step.
Step 7: Heating the Floor of the Oven and Mounting the Oven
To heat the floor of the oven, two tube burners were built. These burners are of my own design that I used for a DIY griddle and BBQ replacement burners.
The burners were made from some stainless steel 1" tubing with slits cut and an iron pipe reducer for the intake. The orifice was made from 1/4" brass nipple and fittings. I won't go into deep details on the construction of the burners as you can see the build in a previous Instructable here: https://www.instructables.com/id/How-to-Make-a-BBQ...
To mount the burners I made a bracket and held them in place and welded the ends to the frame. The burners were plumbed into the main burner that was installed in the previous step. Looking at the pictures or watching the video is much easier than trying to read how I did it.
On top of the burners the floor of the oven was mounted. This as mentioned earlier is 1/4" mild steel plate. The reason why the floor is mild steel and not stainless is because mild steel is much better conductor of heat than stainless steel. The mild steel floor was then bolted to the frame using some welded on brackets and holes tapped into the frame.
The oven body is now ready to be mounted on to the floor and frame.
The body was mounted by welding a few small 1" stainless tabs and holes tapped into the mild steel floor. A door was also made so it could hang off the front of the oven. While not necessary, it does help keep some heat in the oven.
Give the whole unit a polish and it's ready to cook pizzas.
Step 8: Cooking Pizzas
So this Instructable is about building the hardware too cook a pizza. I'm not going to go into too much detail on making pizzas.
I've used the oven a few times and it gets blazingly hot. I can control the heat to any temperature and hold it for an indeterminate period of time. The temperature gauge maxes out at 800F and I've had the needle goes well past that. From that I can tell it's well over 1000F, and the floor temperature of the oven can be fine tuned by controlling the heat of the floor burners. The first few times when testing the oven I burnt the bottoms of the pizzas in less than 30 seconds as the floor was way too hot!
So for the dough of the pizza I went with a simple Neapolitan pizza based on the Serious Eats recipe (Google it).
After some testing, I was able get excellent results, far better than I expected. Pizzas could be cooked in a minute depending on how many toppings and thickness of the crust. True Neapolitan style pizzas are cooked in under 1-2 minutes.
The pizza is slide into the oven with a wooden pizza peel with a light dusting of corn meal or flour, I learned to not use a metal one as dough tends to stick, wooden ones allow the dough to breath a bit. The metal pizza peel is used to remove the pizzas. Once the pizza is in the oven, I let it cook for about 30 seconds, then I use a spatula to rotate the pizza, as one side of the pizza cooks faster than the other side. Depending on how the pizza is cooking I rotate it as needed. After about a minute, I get ready to remove the pizza once the amount of brownness on the crust and topping is achieved. If the pizza starts cooking too fast or slow on the bottom or top, I adjust the heat to either one of the burners.
I get a nice airy crust because the pizzas cook so fast from the intense heat with a nice spotted bottom to match.
Step 9: Lessons Learned and Final Design
If I were to make another one of these ovens I would change a few things. First off, I would not bother to insulate with the thermal mass of high heat refractory cement. While the thermal mass is important, i think it's really only important if you have a burner like the wood burner that doesn't produce a ton of BTUs at once. This adds far too much weight if you want the unit to be portable.
The direct heat of the propane flame is powerful enough to cook a pizza just by being close to the flame. The heating of the floor really is nice as you can control how crispy or dark you want the crust.
After some use, I figured out that the pizza dough needs to be super thin, keep the toppings to a minimum so the pizza can cook around 1 minute and then it will be similar to true Neapolitan style pizza.
This oven can cook more than just pizzas, naan bread can be cooked in seconds and any other type of quick cooking foods, I'll find more applications for this oven I'm sure as I use it.
This was a super fun project to build and troubleshoot. I think a similar oven could be made lighter by just using a metal deflector plate where the flame of the burner hits the back of the oven. The cement refractory is probably not necessary as originally I wanted to use a wood fired burner, as the cement provides a huge about of thermal mass.
So it is possible to cook a pizza in a beer keg, provided you have a burner that can heat it up to 1000F!