This is how we make small quantities of charcoal at home. I don't consider this a method for producing charcoal for sale, but it's good for using the small piles of sticks we get from cleaning up around the house.
- Materials are free or almost free to make charcoal this way.
- Yield of charcoal is around 2 full-size hessian potato bags, or 25 to 40kg.
- A burn takes 4 to 8 hours, depending on the wood used.
- A properly sealed drum should be cool and ready to bag in the morning after cooling overnight
- It's much more efficient to use 2 (or more) drums - side by side allows long sticks to be burnt over both
- This charcoal is good for cooking, blacksmithing or biochar
Fast Burn MethodThis is a “fast burn” method, meaning that the wood is burnt in a flaming open fire, for a relatively short time.
The other method frequently used is the “slow burn” method, where wood is burnt in a closed container, without flames, and producing lots of smoke. I don’t know how to do that, but it is the most common method traditionally.
Slow burn methods tend to produce more charcoal from a given amount of wood, but are smokier and take longer.
1. Materials and tools To make charcoal this way you will need:
- A steel 200l drum. The drum must not have any rust, bullet, nail or other holes.
- Some scrap round steel bar, from 6 to 12 mm diameter, to make skewers.
- A chisel to cut the drum’s lid off.
- A roofing punch (or similar) to punch holes in the drum.
- A shovel.
- Something to cut the wood with – axe, saw, chainsaw, strong arms…..
- Some way of sifting the the ash and fines from the charcoal – seive, a 20l drum with holes punched in the bottom, something else…..
2. Collect wood.
You need a good pile of wood ready before you start.
Imagine the drum full of solid wood, with no spaces – that’s about how much wood you need, which is a lot of wood. Be very careful not to use chemically treated wood. Even painted wood can produce toxic smoke and ash.
Any wood will make useable charcoal, but different woods make different qualities of charcoal:
- Thin wood cooks faster and works better than large lumps and stumps in this method.
- Dry wood burns quicker, and avoids the waste of charcoal while water is boiled away.
- Denser woods make denser charcoals.
- Different trees have different ash contents – rainforest trees and wattles tend to have a high ash content, eucalypts tend to have low ash content. Low ash content is preferable in a forge, but all charcoal is useable. E.g. Gidgee is very dense wood, which makes dense charcoal, but which produces so much ash it can clog the forge if not cleared frequently. Chinese Elm charcoal has a high ash content. This is less of a problem when fires are made for short periods before cleaning, e.g. cooking fires.
- Bark has a much higher ash content than wood, sapwood has a higher ash content than heartwood. It is better to burn as little bark as possible, but I am always happy to make charcoal from sapwood.
A normal, steel, 200l drum with 2 bungs in the lid is best. I have found this to be better than the other less common types with clip-on lids etc.. One of these can usually be acquired for free.
- Cut the lid off. I prefer a wide, bevel-edged wood chisel (not one intended for woodwork) for this job. Hit it with a wooden mallet if you have one, or a hammer if you must. Cut around the top of the drum, inside the rolled edge. The flat sheet metal lid should drop to the bottom of the drum when you get all the way around.
- Prepare 2 skewers.Make these of round bar, long enough to go through the holes you are about to punch (see below), and stick well out both sides. Use bar between 6 and 12 mm diameter. I like to forge a rolled eye on one end, and draw out a blunt point on the other end.
- Punch 4 holes under the rim. These should be evenly spaced, just under the rolled rim of the drum, big enough for the skewers you’ve just made. I use a pointed roofing punch. Punch from the inside of the drum, to cause the split steel to be bent outwards instead of into the drum. This will avoid obstructing the lid being put in place. When you make the charcoal, you will need the drum, the lid, and the skewers.
4. Start a fire in the drumLay the drum on its side on the ground. Light a fire in the mouth of the drum. Build a strong fire in the mouth end of the drum, and give it time to grow a bed of coals, which will be able to survive the drum being stood up.
5. Stand the drum upright
Use the shovel, or a stick, or something else, to stand the drum upright. The fire will fall down in the drum, and will take a few minutes to re-establish.
6. Feed the fire
Once the fire is re-established in the upright drum, it needs to be fed. It’s good to use long sticks for the first hour or so after standing upright.
These keep a more open fire, allowing air and heat to cook the wood closer to the bottom of the drum.
They also provide a cradle for heavier, shorter pieces, preventing them from falling to the bottom of the drum and remaining unburnt.
As wood burns, it breaks up into coals, and they fall to the bottom of the drum where air is hard to access. Any unburnt wood covered with charcoal in the bottom of the drum will be starved of air and will stop burning. Keep enough wood burning in the drum to consume most of the air, and protect the charcoal at the bottom from being burnt. At times the fire can become very smokey, especially when new, cold wood is added to the fire. Adding smaller amounts more frequently can avoid this, and make for a faster, hotter burn. As the drum fills, shorter pieces of wood will be needed. Longer pieces will burn off and fall out – watch for grass fires and burnt shoes!
7. Seal the drumWhen the drum is filled nearly to the top with charcoal, and you can see that you are starting to burn the coals as well as the wood, it is time to close down.
Remember: once the drum is sealed, the charcoaling stops completely. If you seal the drum too soon, you’ll be making a drum full of black wood.
You need to place the lid on top of the charcoal, low enough that the skewers may be threaded through the holes, above the lid. This may require removing some pieces of wood from the fire (probably with a shovel).
With the lid on, and the skewers in place, the drum is now tipped upside down. If you don’t dilly-dally, the skewers will still be cool and can be grasped by hand to tip the drum on its side. The bottom of the drum, which should be cool by now (seriously yes – the fire has not been at the bottom for some time by now) can be gripped by the rim by hand, and lifted up to leave the drum upside down.
Dirt is now shovelled around to seal out air.
Once the drum is tipped and sealed, no more charcoaling will happen. When you open it up, the contents of the drum will be just the same as when you sealed it, just cooler.
8. Seive and bag the charcoalThe next morning before the sun shines on it, feel the bottom of the drum (now at the top) with your hand, to see if it is still warm. If it is still hot, there is probably an air leak, either from rust holes in the drum, or a poor air seal at the dirt end. Seal the leak and wait another day. Don’t open it until it is cool!
Danger: it is possible for coals to remain alight in the drum. A bag of charcoal with a live coal inside could catch fire, and burn a vehicle, house or shed, or start a bushfire. Remember you are working with fire!
It’s good to seive the charcoal before using it, to remove any ash or fines mixed with it. About 10mm wire mesh is good. I’ve used 5mm perforated steel for many years to seive charcoal, which is good for blacksmithing, but leaves rather too much fines for cooking (so you save the bottom of the bag for the forge).
I use a bagger (pictured) for bagging large quantities, with hooks to hold the bags. I’ve also punched 12mm holes in the bottom of a 20l drum, as a slow but useable seive. Wire mesh is much better.
The fines and ash separated from your charcoal are also valuable as a soil improver. They can be dug into a vegetable garden, or spread under fruit trees. The ash from the charcoal forge or cooking fire can also be used in the garden, but be cautious not to overload the soil in one place as ash is strongly alkaline.
I then sew bags shut with a bag needle and string. Store your bags of charcoal out of the rain. Water will make the charcoal sparky and hard to light, and rot your bags.
9. Protect your drum from rustingOnce the drum has had a fire in it, it will be very vulnerable to rusting. It won’t take long to develop rust holes which will waste your charcoal by admitting unwanted air during and after future burns. I recommend coating the outside of the drum with sump oil, and storing it under shelter.
10. Using your charcoalThe charcoal you make from wood can be used for blacksmithing, cooking, or soil improvement. Charcoal is a smokeless fuel, which will not blacken pots or hurt your eyes when cooking.
Caution: Charcoal fires emit colourless, odorless and poisonous Carbon Monoxide gas, so must not be used in confined spaces. Burn your charcoal in a place with good ventilation (open windows, open doors, or outdoors).
Charcoal and firewood are “greenhouse neutral”, or “carbon neutral” biomass fuels, when produced from sustainably grown forest. The carbon dioxide released when charcoal is burned, is equivalent to what would be released were the wood to decompose naturally, and equivalent to what the forest will absorb when re-growing. Happy cooking!
For more discussion of using charcoal in soil - biochar - see my page: http://bruceteakle.blogspot.com.au/2017/01/quick-and-easy-biochar-in-200-litre-44.html