After some four years of prototypes, including Bertha 1 and Bertha 2, Luna, the woodfired oven, landed. With precision.
It's amazing what I have learned from building and using ovens - both woodfired and 'on the grid'. If I had a dollar for every time I cursed Bertha, the name we gave our first two commercial prototypes, I'd have built another ten ovens by now with the proceeds.
Bertha 1 was a swiss army knife - a cafe cooker and a baker's oven. She had a useless bottom deck, and arrived without any insulation. She burnt all the hairs off our chef's (a brave man, was Paul West, later to go on to become the host of River Cottage TV show) legs so many times they had to wear long trousers, even in midsummer. She burned out the cafe exhaust system, and melted herself out three times in three different places. Despite all this, I managed to tune her effectively enough to pump out a couple of hundred awesome loaves every Saturday morning - and she handled her cooktop duties well, after lots and lots of tweaking. She really was a comedy of errors, though, and the best learning facility a baker and a boilermaker could ever have.
Bertha 2 was more focussed - a purpose built baker's oven from the getgo. She still managed to burn out her first firebox inside 6 weeks, but when we replaced much of it with stainless steel, she ran like a trojan. Then I almost destroyed the bottom deck by accidentally setting a fire inside it (seriously!). She was made of stern stuff, and survived nonetheless, with more brick being added in there. Bertha 2's big problem was that she was designed for 7 day a week service, but in the end she only got to be used for two or three days. As a result of her reduced role, her unsuitedness to short baking shifts really became a major issue. She weighed probably more than 4 tonnes when fully tuned, and it took a full day to get those bricks hot. In addition, her insulation and flue design needed major work, in order for her to heat both decks within a reasonable time frame evenly.
Again, so much was learned. On to oven number three - a make or break proposition for me, as both Berthas had cost me so much time and lost product due to their many design and application faults, I simply couldn't afford another 'crash test dummy' scenario playing out.
This time, Craig Miller and I spent a whole lot more time on the design and the assembly - almost twelve months in fact.
The brief, this time, was very specific, as I wanted to build a mobile bakery and the oven was to be the centrepiece. It was as follows:
Make a lightweight woodfired oven that can be towed by a vehicle - less than one tonne in weight if possible
Design it to heat up in an hour from cold
Design it to heat evenly, top, bottom, sides and back, so that it will be easy to use
It must be super fuel efficient so we dont have to lug lots of wood around
It must be very clean, so public places don't fill up with smoke when it's used
It must be capable of baking 250 loaves in 5 hours
It must be able to accessed internally easily, and should be able to be fixed with a screwdriver, a drill, a hammer and a crowbar. Third world simplicity.
Well, now it's built. We called her Luna, because she looks like a lunar landing craft. How did we go, against the brief?
Well, not too bad, overall. I've used her for the past nearly five years at the time of re writing this article (Jan 2018), and to be honest, she does pretty much answer the brief in some areas. But not all.
She weighed about 1.5 tonnes when we first built her - now she weighs about 3 tonnes, so she ended up a bit heavy. I'm not sure if it's possible to answer the baking capacity question with a lighter oven though. 1.5 tonnes can be towed - which was important when the idea was to bake on site. The problems with this idea became evident slowly. It’s worthy of a blog post about the drawbacks of baking in a mobile bakery, but this isn’t it.
In short, I decided to use the baking trailer as a moveable bakery, rather than a mobile bakery - there are just too many things to think about when you move your bake from place to place, and it’s quite difficult to physically move many tonnes of stuff on a regular basis as well.
Thus, as towing the bakery became less important, I added a whole lot more thermal mass to Luna. It's hard to be accurate how much weight I piled in, but it has been worth the overall weight gain, as the baking power is so much better with more thermal mass.
If you blaze it, she heats to baking temperature in two hours from cold. Doing this will provide a baking deck or two in this time. Really, though, Luna takes a good four hours to really 'soak'. The ‘heat up in an hour’ part of the brief is almost doable, but the oven works better if time is structured in to the routine, so that Luna is nice and hot by the time she is used.
Of course, if I were to bake with Luna more than once a week, she would retain heat much better, so heat up times would end up being around an hour, so that part of the brief is satisfied.
Once she is soaked, she is very even. All that extra thermal mass has a purpose. Luna has met that part of the design brief easily. She is a superb oven to bake in.
She is super fuel efficient - she runs mainly on sticks, with a bit of lumber or food waste used for holding hot coals. She uses half of Bertha's fuel, and burns almost without ash - though keeping her clean is very important. Tick that part of the brief off as well. She does produce smoke when she is fed for a little while; this smoke dissipates quickly, and lessens as the firebox bricks take on more heat.
What about speed? She can do more than 250 loaves in 5 hours - the speed of Bertha depends on how much help the baker has, though. On my own, I have too much to do when I'm running a bake to keep that pace up for very long. If I have a helper to do some of the table work while I bake, 50 loaves an hour is a very realistic figure. There are some variables here. On my own, I average about 30 loaves an hour.
Most parts internally can be easily accessed - though now she's on the trailer some of them are not as accessible as they were. And she can be fixed with our third world tools too. I've been inside her once since commissioned, and did a major internal clean and rejig. It wasn't too hard, but I did add an angle grinder to the tool kit at the time. Hardly third world, but I guess if you had the time and the inclination, the job could have been carried out with a hand drill and a hack saw.
So, Craig and I believe we have answered the brief very well. After five years working with Luna, turning out some of the best bread I've made in 30 years of living in this bakery world, I have to say that I already think she's the best oven I've ever owned.
Stay tuned for the technical stuff!
Here’s a video I made about four years after commissioning Luna. She had just had her first ‘Open Heart Surgery’ - where I cut her open, cleaned her right out, and re bricked things to be heavier, with more thermal mass. As Luna was a prototype, we didn’t imagine we would still be using her so many years later. Our ovens are now designed with access points for cleaning. As our ‘crash test dummy’, I get to do the really dirty work. Enjoy!