Making biochar in a woodstove

20140125-080609.jpgWe have been making biochar all winter in small batches by using tin cans we got from some “pirouette” cookies and a paint can that we found in an old garage that was exceptionally clean.  We poked a small hole in the back of the can to let the vapors out while limiting the oxygen that can go back in.  We found that the hole had to be big enough so that pressure does not build up in the can and blow the lid off in the fire.

The idea with biochar is to make charcoal that can then be used to augment soil quality.  The charcoal provides aeration to the soils, sites for beneficial bacteria and fungi, and acts as a sponge for moisture to be absorbed and later released into the soil.  We have some plots with biochar that we will be monitoring and collecting data so we can prove to ourselves that it is indeed augmenting our soils.  We got much information from the book “The Biochar Solution” by Albert Bates as well as a bunch of YouTube videos.  There is also much information about the benefits of biochar around the analysis of the “terra preta” systems in the Amazon in books like “1491” by Charles Mann.

Where most people have dedicated infrastructure to make biochar that uses firewood, barrels, and venting structures; we are making biochar incidentally.  Since we already live in a situation where we run the woodstove to keep warm over the winter, it is nice to use our little biochar chambers to make small batches at a time.  So far we are just using the left over corn cobs from our harvest to make biochar, eventually we might utilize other pieces of wood.

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A concern about this method is the question if any residue from the tin cans gets on our biochar that could negatively effect our soil quality.  We will be doing more research on this to make sure but in the meantime we are mostly using biochar that is leftover from the process of using our horno mud oven, which is undoubtedly safe since it is just a mud chamber.  If any readers have any information about the potential contamination of our biochar from the tin cans, we would be happy to hear about it.

We are also interested in using the biochar for water filtration and want to start showing people how to build water filters using a bucket, some sand and gravel, and charcoal in alternating layers in the bucket

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About Miguel

Miguel Santistevan is a researcher, educator, and advocate for traditional agriculture crops and systems.
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2 Responses to Making biochar in a woodstove

  1. Merlin Branigan says:

    Hi I have done the same in a cast iron casserole pot with lid. The lid is quite heavy so I don’t need to seal it or make a hole as the lid lifts with the build up of pressure, and seals again with gravity. I have experimented with different materials, but have found twigs and wood chips not too tightly packed work best.

    • Miguel says:

      This is an awesome adaptation that might actually work better than the process I am experimenting with. Cast iron seems like a better container for the purpose, I find that my tin can method only works for so many iterations before it starts to deteriorate. Thanks for the comment!

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