Biochar in the Making

Biochar Burn Demonstration

It’s Gonna be Hot, Hot, Hot!

Ever wonder how to make your own biochar?  Wanna learn?

Fresh Steaming BiocharIn the beginning years of Hawaii Biochar Products there were no fancy machines, only wood and sweat, lots of sweat.  With a large supply of clean dry wood from local sawmills to play with, I developed a technique that proved to be a very efficient way to transform wood into biochar.  Many different approaches were attempted, those will be discussed as well, but the focus of the day will be the live demonstration of the winning technique – Open Pit or “Imu Style” Biochar Burn.

Mark your calendars for Wednesday, June 12.  This biochar burn demonstration is sponsored by Kalani, Hawaii’s largest retreat center, based in Opihikao on the beautiful Puna Coastline.  All that is needed for entry is a $12 dollar fee, which also gets you a meal ticket to their local-centric lunch buffet.  Start time is at 10:00am, the fire will be done by 3pm, conversations will carry on for hours.  Lodging is available.  Call 808 965-7828 for more details.

Hawaii Biochar Products has far more advanced production facilities now (a story soon to be told), but this technique is still used for home production on my own farm and has been taught to many others for production on their farms.  It is estimated that in the last 5 years more than 150 tons of biochar were produced and sold from my own backyard using this approach!

The concept is rather simple, but the details are important.  I will cover the basic concept below, but if you are interested and available I highly suggest you make it to the demonstration for the first hand experience.

It all began on flat ground.  It grew into a pit to gain greater air control.  Wood burns twice, once from wood to char, then from char to ash.  The second part can only happen with oxygen.  On flat ground the char produced during burning is hard to protect from oxygen entering from the sides.  In a pit, the char is covered as it is produced.

First, a fire is started in the bottom of a pit, then dry wood is then added as fast as the fire will allow – you must always push the fire near to the point of smothering it, yet without actually smothering it.  It is important to always keep a clean burning fire – no smoke.  If it becomes a bit smoky, back off, let the fire catch up.  If it is raging, add more wood to choke it out a bit.  In this way youare constantly covering the char that has been made with fresh layers of wood, which become char, which are soon covered with fresh layers of wood, which become char, and so on. When you near the top of the pit or the end of your wood supply, you finish with small diameter wood.  This chars quickly.  Let the flames die down a bit, then voila – a large bed of red hot glowing coals.  By this point, if you have done it right, the entire pit has turned to char.  You can either hose it down immediately, or cover it with soil to snuff it out, then uncover it a few days later and hose it down.  Look to the pictures below for a visual reference.

Biochar Burn Picture #1Biochar Burn Picture #2Biochar Burn Picture #3Biochar Burn Picture #4Biochar Burn Picture #5Biochar Burn Picture #6Biochar Burn Picture #7

Harvesting and grinding the char is a job all unto itself.  You must be very careful to make sure that all the embers have been extinguished or the entire pile can re-ignite.  Always follow local fire safety regulations.

To cook in the pit, dig a hole in the embers, line the bottom with crushed banana stumps, place food wrapped in leaves, cover with embers, smother with soil, uncover later and enjoy.

Have Fun, Be Safe,

– Josiah Hunt

All Photos By Josiah Hunt



  1. Dear Josiah Hunt,

    Invaluable information. There’s seems to be such a paucity of information on simple biochar production at the household scale, so thanks for sharing this.

    I’ve heard from a biochar enthusiast that suboptimal biochar (that still contained many volatiles) was less of an issue than the papers recommending retorts for high temperature pyrolysis suggest. He asserted that bacteria would, eventually, deal with these volatiles and render the fine biochar lattice open and comparable in surface area to that produced under more controlled, industrial conditions.

    Does anything you’ve read or seen back this up?


    Ben Scriven.

    • Hi Ben,

      I believe that theory has some truth to it. Be careful though that you do not mistake the lack of industrial conditions for the lack of ability to produce “optimal” char. Whether with a multi million dollar facility or a recycled tin can, one can make a wide variety of chars. One issue with using char materials that are cooked at low temperatures and contain high levels of “volatile matter”, as can be found with hardwood lump charcoal designed for BBQ’ing, is that there is often a lag time seen before any positive plant growth response, even possible negative response. The technique outlined in the post can produce very high quality biochar materials when done with care.

      Best Regards,

      – Josiah

      • Hi Josiah,

        I’ll bare that it mind. Amazing how such “nanotech” can be so low-tech! Thanks so much, I can’t wait to see where all this potential leads.



    • I have two interesting references to using resinous fire byproduct as fertilizer. The first is from Nutrition and Physical Degeneration by Weston Price. He talks about these islanders who build thatched roofs with no chimney. peat fires burn in the houses all the time and every year or two the harvest the entire roof for fertilizer because it is saturated with smoke residue. The other is from Farmers of Fourty Centuries. The chinese use these beds that are flue heated and built from adobe. Every so many years, the whole bed is actually sold to be powdered and used as fertilizer because the creosote deposited on the inside is so valuable! Makes me wonder what can be gotten away with and what is actually beneficial v.s. dangerous or inhibitory.

  2. Way cool. I’ve just did something like this recently after hearing about the Japanese cone kilns. I made the pit long to reduce wood cutting, but it was a small pit. There are some cool things about this method. How many methods are this accessible? Anyone can dig a hole. Also, using the hole to plant in after seems like an obvious thing to do. I’m laying out some new apple tree sites so I can try doing just that. I’ll dig a 6 to 8 foot diameter pit, burn enough charcoal in it to amend the spot with x% char, and then integrate the char into the soil along with other amendments as it is reburied (after grinding somehow). Also, few methods can use odd shaped brush. I’m hoping I can get away with using all manner, size and shape of brush including green wood. Reducing wood to fit into various containers used in other methods is often prohibitively labor intensive when using limbs and brush. Do you make the cone shape on purpose? I think it helps smother the fire better, or at least that’s my thinking, and my observation based on just a very little experience.

    I think there are more places to go with this as well, such as integrating char into the soil when doing forestry work. If green brush can be use in almost any size and shape just managed like a gradual burn pile (which is how I run my burn piles anyway) that is a huge bonus in efficiency of char production. I’ll be trying it out as soon as I site my trees. I just did a short article on my pit burn experience. I also used the residual heat to cook some agave leaves for fiber extraction.

  3. I was wondering the approximate dimensions of the hole n the ground.

    Thanks Mike

    • Hello Mike,

      The cone shaped pits that are featured in the photographs are about 8 ft wide, 4 ft deep, and built into the foot of a slope with the predominant wind aiming at the face.

      – Josiah


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