Cob Ovens: A Sustainable Option for Summer Baking

cob oven

Because we don’t have central air conditioning, we try to keep our house naturally cool during the summer. That means we cook indoors as little as possible. Through the years, we’ve used a modern grill on our deck and then we added a solar oven. Ultimately we built a cob oven. The main thing I love about having a cob oven is that it gets us one step closer to self-reliance. There is no electric or gas bill associated with us using it. The wood comes from our farm.

Cob is a traditional building material made of clay, sand, and straw. It creates a thermal mass, which absorbs heat from the fire, then stays hot for several hours. It doesn’t have a chimney, as the smoke billows out the door. After the fire has been going for a couple of hours, the coals are traditionally raked out. The door is placed on the oven to let the heat equalize for a few minutes, then we place the food in the oven for cooking. The temperature is usually in the upper 300s, although it has been more than 400 a couple of times. Sometimes, instead of raking the coals out, we simply push them to the side if we want our food to taste smoky. Since we have hickory trees on our farm, we use the hickory wood so that we can have real hickory smoked chicken or ham.

The base of the oven was built on a concrete pad. We created a ring of bricks and then filled the open space with empty bottles. Then we filled the space between the bottles with sand. We covered the sand with a layer of clay, which created the oven floor. The bottles insulate the oven from the earth, so the oven will stay hot longer.

To create the cavity that will be the inside of the oven, we created a large mound of sand, which was later pulled out when the dome of the oven was hardened. The dome is made of three layers. The first layer is a mixture of sand and clay. The second layer contains empty glass bottles for insulation, with sand and clay between them. The top layer is clay, sand, and sawdust. After it dried, and we’d used the oven for a few months, we added a layer of lime plaster with fabric dye for decoration. The oven needs to be protected from hard rain at all times. For now, we put a tarp over it when it’s not in use, but eventually we plan to build a shelter with a roof over it. This will also make it nicer for us to use it when it’s raining or extremely hot and sunny.

homegrown and handmade

This is an excerpt from the second edition of Homegrown and Handmade: A Practical Guide to More Self-Reliant Living

6 thoughts on “Cob Ovens: A Sustainable Option for Summer Baking”

  1. Very stupid question, and one you’ve surel heard a zillion tmes before: Won’t the bottle explode when heated and cooled again repeatedly?
    And urgh! Books are expensive in Denmerk where I live. Yourbook costs $10 more here 🙁

    • I don’t think they’d explode, but the glass bottles (and small glass jars) are sandwiched between layers of the sand and clay mix, so even if they do explode, you’d never know because they’re encased in the “cob.”

      That’s really sad that books are so expensive in Denmark. And I know from past requests that it would cost me about $20 to ship the book to you, so that wouldn’t save you any money either. 🙁

      • Yes that’s sad – and it is even worse. I have to pay a tax to the state on every item from USA costing more than $12 (the tax is $24). Importing things from USA apart from a bag of seeds or a hank or two of yarn is only an option for rich people or firms. 🙁 I don’t know if this is an EU thing or a Danish one. Stupid it is in the extreme.

  2. A possible suggestion for those writing about the taxes on US imports, could you request that your local library get a copy to lend. My library does this so willingly, and it helps their collection– and me!

    My question, without reading the 2nd edition, is how you keep the layer of bottles in place until they are covered?

    • We created a ring of bricks and then just stood the bottles in there and covered them with sand. Some of the bottles are standing upright just like you’d set them on your table, and some of them are upside down between the bottles that are standing upright. The upright bottles hold the upside bottles in place.

  3. I suppose making an e-book instead
    that people would still have to pay for would spare the readers printing and postage costs of the actual book but it would not deprive them of all the useful info it contains


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