A wall oven customized for bread baking

I started baking bread at home circa 2020.  I watched a few John Kirkwood videos which made the whole process seem reasonably simple. Much to my surprise my first attempt yielded a bread superior in taste to anything I could buy from my local in-store supermarket bakery.  I was instantly hooked.  My main pursuit since has been the elusive “perfect baguette”.

Part of achieving that beautiful crust that is so characteristic of the baguette is providing steam at the beginning of the bake.  I used a gas range oven when I started baking, so my ability to control and retain steam was limited.  Being an engineer, I am prone to tinkering which led me to convert an unloved espresso machine boiler and water pump into a steam generator.  I managed to rig this thing up to deliver a constant flow of steam into the oven from below via some stainless steel tubing.  It was effective as I noticed a marked improvement in the crust of my baguettes.  However, this also required a fair about of time to set up, operate and put away (for some reason my wife wouldn't let me leave it on the countertop between baking days). 

All of this worked well from about October to May when the oven’s heat could be put to good dual use in warming the kitchen on baking days.  But I dreaded the idea of baking during the summer when the air conditioning is running (I'm cheap too!).  I tried baking bread on the propane grill with mixed results, and this took a lot more effort. 

In addition, my kitchen oven is gas and with that comes a big vent.  This makes it difficult to develop and maintain a high steam environment without the use of an enclosure like a Dutch oven or an inverted aluminum foil pan. This prevents you from watching the oven spring and it limits the size/shape of the loaves you can bake.  I was also curious about convection heat and how it would impact the final phase of the bake.  After much (some might say excessive) research and planning I finally decided to buy a wall oven and customize it for bread baking. 

I found a gently used 24" GE Profile convection wall oven (model PT7050FS2SS ) on Facebook Marketplace for $150.  I found a set of used kitchen base cabinets which I cobbled together to make a 30" wide base cabinet and added a set of floor casters for mobility.  I also made a fold down shelf for each side of the cabinet so there is room for staging the bread and cooling it afterwards. It currently resides in my garage where I installed a 240V-30A outlet so I can bake over the summer without having to AC all that heat out of the house.  In the end, that $150 oven turned into a $350ish project.

But being an engineer, that just wasn't enough, I could do more to improve the process.  So, another $200 for widgets like a Raspberry Pi computer, a 7"touch screen, a peristaltic pump, a stepper motor driver and a bunch of sensors and other electronic doodads and I have finally completed Phase 1 of "Project Oven" with the following capabilities:

• Programmable water injection for controlling steam generation.
• Timers automatically activated by oven door sensors or touch screen (so I don't forget anymore!).  Add/subtract time as the bake proceeds.
• Camera recording of the oven bake process so the images can be stitched together to create a short time lapsed video with time and oven temperatures embedded in the images.  You can watch the entire bake from oven sprint to color formation in about 20 seconds.
• Individual baking recipes are stored in a data file so you can repeat exact oven cycles.
• Measures up to 4 thermocouple and 2 RTD temperatures for a full thermal history of the bake.
• Recording of oven heating element on and off times (yes, truly an overboard feature!)
• All oven data saved in a database format for easy future retrieval.
• High-temperature mode for baking pizza.  It effectively suppresses the measured temperature by a factor of about 0.7X, so with a setpoint of 550°F the oven is actually at 750°F (still well below the peak 880°F temperature of the oven’s self-clean cycle).

The most noticeable improvement is in the consistency of the steaming process. The small peristaltic pump injects water onto the surface of a preheated 11 lb. cast iron griddle on the floor of the oven.  Inside this griddle is another 5 lbs. of 1/8" diameter stainless steel balls which provide more stored energy and a lot of surface area to promote rapid vaporization of the injected water.  When preheated to just 450°F it can vaporize over 150 mL of water in under 30 seconds at the onset of the steam cycle and an additional 150 mL over the next 5 minutes. Altogether that’s over 15 ft³ of steam generated in 5 minutes inside a 5 ft³ oven cavity – that’s a lot of steam! This simple system works really well and is much safer than pouring water into a pan.  The only necessary modification to the oven for this feature was drilling a ¼” diameter hole in the side of the oven for the stainless steel tube (a fairly simple task).  The peristaltic pump is just one method to deliver specific amounts of water.  Pouring water from a measuring cup into a funnel connected by flexible tubing would also do the trick (but not as fun as spending hours writing C++ code to drive the pump at precise speeds!).

I have also found switching to convection mode after the steam cycle greatly improves the uniformity of the final bake, especially with respect to color development (I no longer need to rotate the baguettes or shuffle the ciabatta rolls to get uniformity). The automatic start/stop of the timer feature works really well.  No more guessing how long the bread has been baking because I forgot to start the timer!

I tried the pizza mode once and got the oven to 750°F.  With that I was able to cook a Neapolitan-style pizza in about 2 minutes (just like a wood fired pizza oven).  I have now added pursuing the perfect Margareta pizza to my culinary to do list.

I have also begun cooking other things in this oven using the convection mode.  Roasted potatoes are significantly better when baked with convection heat.  Our next kitchen will definitely have a convection wall oven(s). 

Phase 2 of Project Oven is already on the drawing board.  First up is installing an electric outlet in the basement so the oven can reside there during the winter months.  I live in New England, and I don't relish the idea of baking in the garage in January.  I also discovered that there may be a way for the Raspberry Pi to send oven setpoint temperature and operation mode commands directly to the oven controller board by passing the need to use the control panel.  If I can get this to work, then I could also include oven preheat and bake temperatures in the stored recipes.  I would no longer need to remember baguettes are baked at 450°F and ciabatta at 475°F (or is it the other way?).

I also plan to experiment a bit with using a fog injection nozzle located above baking stone.  I want to see if enough water, in the form of tiny droplets, can be deposited onto the dough surface before completely evaporating.  The idea here is to help keep the dough surface moist and extensible during the very initial phase of the steam bake without the added heat that comes from steam recondensing on the dough surface.  This might just enhance the oven spring by extending the life of the yeast.

Lastly, I need to regrind the oven door glass.  I ground off a small 3”x4” section of the heat reflecting coating on the inside of the oven door so the camera would have an unobstructed view of the oven interior. But my first attempt ended up with some surface irregularities which cause optical distortions preventing nice sharp images.  Getting this surface back to an optically flat condition will greatly enhance the quality of the images captured by the camera and ultimately justify recording images at 4k resolution.

I tried adding some pictures but they are getting inverted during the import, and I don't know how to rotate them back.