The fire is burning merrily in the cob oven. Photo: Smallholder Training.
The completed foundation for our cob oven. Photo: Smallholder Training.
Mixing the cob in our farm yard. Photo: Smallholder Training.
Trampling the cob - fun, fun, fun! (Feel free to do this to your favourite disco beat). Photo: Smallholder Training.
Green cooking in a cob oven - and how to build your own
Debbie Kingsley & Andrew Hubbard
7th June 2014
Ever thought of building a cob oven? Maybe you should, write Debbie Kingsley & Andrew Hubbard, for fossil fuel-free cooking that warms up every party, perfect for everything from pizza to roast vegetables or your (organic) Christmas turkey ...
The cob oven makes a fabulous focus for a party or community celebration.
Why would you want a cob oven? Well, how about because it's a thing of beauty, made of natural materials with no need for fancy equipment?
It's also easy (and great fun) to create, very easy on the fuel bills, and a permanent feature that you can use again and again ...
Add to that, it cooks absolutely fantastic food, baking and roasting a huge variety of dishes including authentic crispy pizza, crusty bread and succulent roasts.
Because it's so superheated it cooks food incredibly quickly, less than 5 minutes for a huge pizza or 45 minutes to roast a large duck.
It's too good (and big) to use alone ...
A cob oven also brings together friends and neighbours, forms a centre piece for all sorts of fun occasions, like parties and community celebrations.
We've built one with a community group in Cornwall and taught youth leaders in Devon how to build one that they will use with children learning to connect with their local environment.
The generous size of a cob oven means you can cook several loaves or joints of meat at one time, and create mounds of sweet roast vegetables generously sprinkled with chilli oil or other flavoured oils and herbs.
Many hours of cooking ...
It takes a morning to fire up the oven, but once it's up to heat it cooks for many hours, so it's the perfect party and community activity. With one or two people stoking the fire, the others can work on preparing the food.
If you're ravenous, the pizzas should be the first to go in as everyone can satisfy their first hunger within minutes. Then you can put in roasting joints, bigger than any one family might consider polite, or heaps of lamb, chicken or vegetables as kebabs or in hunks, on the bone or off.
Flatbreads work brilliantly well in a cob oven, but when it's fired we also use ours to cook everyday sourdough loaves, baked potatoes and more.
But there's no need to stick to savouries; sweet pies and tarts and crumbles are great, although you might struggle to make a decent sponge cake. When the oven starts to cool down you could try a tray of meringues. You can also use the last of the heat for drying mushrooms, tomatoes and other vegetables.
But first, you have to build it
The key material you'll need to build a cob oven is ... cob - a mix of sand or aggregate and clay. A small proportion of fibre such as straw, rush or heather is often added to improve strength and reduce cracking.
Traditionally cob was used for building houses and barns, and of course ovens as it withstands high temperatures surprisingly well. Cob is cheap in terms of materials - especially if you can dig it up on site.
Its greatest enemy is wet: even when rendered it cannot tolerate prolonged soaking from above or the ground. The saying goes, "cob needs a good hat and a stout pair of boots." In Devon, where we live, cob buildings are found everywhere, traditionally thatched and built on a stone plinth.
Mixing enough cob for an oven (you'll need at least 6 barrow loads) is best done with shovels and feet. Clear a good space - several square metres at least - on a paved yard. Mix the aggregate and clay roughly with a shovel, then get your wellies on and start treading.
Better still, invite a group of friends and open the cider. Treading makes sure that any lumps of clay get broken down and properly incorporated, which shovelling alone won't do.
Choosing the right position for your oven is critical. It's a seriously weighty structure and definitely not something you can move once built. It'll need a roof to sit under, and a solid surface to sit on. And make sure that there's no trees or plants that will get damaged by the hot smoke.
It's also a good idea to get a few helpers in - the more people involved in building it the easier the task is, and undoubtedly more fun.
We built the base for our cob oven from heaps of old stone we had in the garden. The floor of the oven will need firebricks - we sourced ours from discarded night storage heaters.
Next, build a dome of damp sand on top of the fire bricks and then cover it in newspaper soaked in wallpaper paste. Form brick sized clumps of cob - free of straw or other fibres - and layer it round and over the dome.
When you have a complete first layer, repeat the process, this time incorporating straw or rush, an armful of dry matter to a barrow load of cob. When your two layers are done, score the surface so that the earth render gets a decent purchase.
Now, cut out your doorway. Make sure it's big enough to allow, for example, a large Christmas turkey to pass. and reaches to about two thirds (ideally 63%) of the internal height of the dome, to allow the fire to ventilate.
Then carefully remove the sand and wallpaper through the opening. A nice sticky wet earth render can then be applied and left smooth or carved to your own design.
A moveable door helps stop the heat escaping and we made ours out of oak - do avoid anything metal as it will get far too hot to handle.
Wait until dry
Waiting to light the oven is probably the most challenging stage of the operation: you need to resist the urge to build a major fire and not expect to start cooking the minute the oven is built.
The more slowly the oven is allowed to dry, the better the chances of avoiding cracks. This applies to both internal and external heat, so protect the oven from baking sunshine too.
You can speed the process up a little by lighting a series of very small but gradually increasing fires in the oven, but be prepared to give your oven several weeks to dry out.
Firing the oven
We're lucky - living on a Devon farm with lots of small fields with hedges that need regular maintenance means we have plenty of hedge trimmings to use to light the oven. Hazel, blackthorn, hawthorn, oak and even willow has all been used. You'll need around 30 to 40 kilos of wood in short stick lengths for a day's cooking.
Start the fire using paper or cardboard and thin pieces of kindling, keep adding kindling until you have a pile of freely burning material then gradually push it back into the body of the oven.
Leave the door off so that the fire can get the oxygen it needs, and the smoke can get out. Add sticks every half an hour until the oven has reached cooking heat which can take 3 to 4 hours.
Note: If the fire isn't getting quite enough air to burn strongly, you can simply drill a few 10mm air holes at the back of the oven near the base to let more in.
At this point the outside of the dome will still be barely warm. When you (or an oven thermometer) think the oven is hot enough, rake out the ash and embers into a metal container and put safely out of reach. Then leave the over with the door on for 15 minutes to let the heat equalise.
If you're going to cook directly on the oven floor and are worried about ash on your food, just wipe the oven floor with a wet rag on a stick.
Learning how to build a cob oven
At South Yeo Farm West, just outside Okehampton on the fringes of Dartmoor, we run a variety of courses for people interested in the rural life.
Over the years most of our hundreds of course participants have been intrigued by the cob oven built by Andrew from materials found on the farm, asking questions like, "What's that? It's beautiful ... can you teach us how to build one?"
So we created a day course to give participants the skills to build an oven using natural materials that you might be able to source from your own land or garden.
It's a very hands-on day and you will work through all the stages of building an oven, from sourcing the materials, shaping the former, building the cob dome and applying an earth render.
We will also cover the theory on the basics of making cob, finding and identifying suitable soils, and techniques for mixing. And of course lunch will be cooked in our own cob oven!
Debbie Kingsley & Andrew Hubbard live at South Yeo Farm West, a smallholding near Okehampton in Devon, where as well as running flocks of rare breed sheep and a herd of Devon Red cattle, and looking after a 2-acre apple orchard, they find time to run weekend courses on all aspects of smallholding.
The next cob oven course is on Saturday 26th July on our farm (which has an abundance of old cob buildings in varying states of repair). The techniques you learn can be applied to the repair or restoration of any cob structure.
The cost for the day is £115 per person. This includes detailed instructions to take away in case you forget the details once you get home; a homemade cob oven cooked lunch; Devon cream tea; and refreshments through the day.
We can also advise about local accommodation - but first see the page on our website.
Using this website means you agree to us using simple cookies.