How to make a mini biochar kiln

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There are many ways to make biochar. I like this small and slow solution because it makes great use of "waste" materials, as well as the heat that is generated by our fireplace.

How to make a small kiln to fit your woodstove

  1. Get two cans, the same diameter. I like to use homebrew cans so I can fit in large sticks.
  2. Crimp the end of one can so it slots into the other. There needs to be small air gaps to relieve pressure as gases are released. If the fit is really tight you can knock a few holes in the end with a hammer and nail. You're aiming for an almost-airtight container, so be creative. I've used an old stainless steel pot with a lid before.
  3. Fill the cans with dried organic material – prunings, nut shells, bones, citrus peels, apricot seeds, even gum nuts; pretty much anything organic (and dry).
  4. Get your fire going well. Best to have some red hot coals in there and some nice flames with medium sized bits of wood.
  5. Lay the cans over the fire and watch. With a hot fire you should see smoke coming out of the can within a few minutes. The smoke should ignite, and blow out from the can like a little flame thrower. After 30 minutes or so the flames will die down, until there are no more gases to combust.
  6. I use large tongs to carefully remove the cans when it's done and sit them on the top of the stove. If you leave the cans overnight they disintegrate quite quickly, so best to remove them when it's done.
  7. In the morning, once everything has cooled, I open the cans to see the resulting biochar. All the material should be very brittle, and make a clinking noise when dropped. Sometimes there are beautiful colours on the surface.

How to use your homemade biochar

I like to reduce the size of the biochar before I 'charge' it. 
  1. Crush the biochar in a container (I use a heavy duty stainless steel bucket) using a wide base piece of wood.
  2. Sieve it down to the required size. I find 10mm and less is a good size. The larger particles will break down further in the composting process.
  3. Charge the biochar - it's like a hotel for micro organisms. You can do this by soaking it in nutrient rich liquid, but my preference is to add it to our bucket toilet system. Each time I make a solid deposit I add in a sprinkling of biochar. It helps reduce the smell and absorbs nutrients. This is later composted, and eventually ends up in the garden.

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