How do you make a fire? When I was a kid, I was taught to put paper and leaves at the bottom, smaller sticks on top of that and larger ones on top of that, creating a cone shape with its point at the top. We light that fire at the bottom and that burns the wood at the top right? Today I’m learning about making charcoal in a Kon Tiki kiln, and it turns out I’ve been making fire upside-down all this time.
There is something about fire that insists we share it, fire invites hospitality and nurtures communities. It is inherently a social object, and is vital to the formation of culture. Fire is that thing that the Greek Gods wanted to keep to themselves. Prometheus and Maui stole it, Loki exchanged it, Mauhita gave it as a gift. The characters that brought us fire often share a spark of curiosity, trickery and deception. Otherworldly, we know not to let a fire take care of itself, there are rules around how to care for it, and how to take care of ourselves. Arguably, fire is a metaphor for the creation of culture, warning us that contradictions in life call for constant reassessment and negotiation. As a metaphor for art, technology and love, fire symbolises sustenance and danger, deception and pleasure, curiosity and destruction. It’s deceptively pragmatic, a driver of social change for millennia. It cooks and makes plates and jugs for the storing and serving of food and wine, facilitates storytelling, makes glass and smelts metal. Charcoal filters water and air, and ash was vital to the creation of soap. Bruce Pascoe in his book Dark Emu on precolonial aboriginal agriculture, describes ashes being tilled into the soil to prepare the ground for yam daisy cultivation.
The use of charcoal in soil is why I’m spending the day with Ruy Anaya de la Rosa and Adam Blakester at Invergowrie in Anaiwan Country. Ruy and Adam are members of Biochar 4 Sustainable Soils (B4SS), an initiative that encourages the safe and economically viable production and use of biochar that meets environmental and ethical standards. Their role is also to encourage sharing and collaboration around the knowledges that are required as biochar develops from a flawed blanket solution to a nuanced and responsive amendment to soils.
So what is biochar? On a basic level, biochar is the efficient production of charcoal enhanced with nutrients. It improves soils by making nutrients and water easily available to plants and provides housing for microbial activity. It immobilises heavy metals, binding them to the charcoal so they aren’t taken up by edible plants. It can change the acidic quality of soils and it sequesters carbon that might otherwise be released into the atmosphere.
The trickier variables of biochar are how it is made, what is it made from, where it is made and what is needed in the soil. Where once it was thought that biochar would simply solve a raft of world problems, such as climate change, Ruy and Adam are working towards a responsive approach, in which the production of biochar takes into account the agricultural waste that goes into making it and the agricultural needs that it can meet. The composition of biochar needs to vary according to the differing deficiencies and resources of the context in which it is used. Biochar improves soil health and can replace or minimise the use of fertilisers across vastly different cultures, economies and environments.
Today we were experimenting with making charcoal for drawing. Adam wondered how fallen branches from stringybark eucalypts would go. Two wheelbarrows of branches are waiting next to the kiln. I have a few dead branches of willow for making into charcoal. Willow, along with grapevine cuttings, are traditional materials for making drawing charcoal. Willow is abundant around NSW and legally speaking, it is regarded as a weed. One of the reasons that it spreads so easily is that it propagates not only by seed but by broken branches. It’s so effective at self-propagating that you can distil its rooting properties into a willow tea that will help propagate cuttings in your garden. Importantly for this discussion, you can’t compost it. It’s going to regrow in your compost heap. So, if you want to get rid of it and don’t want to use poison, you have to deep bury or burn it. If you’re going to burn it, why not convert it into biochar and improve your soil?
Along with the two wheelbarrows full of stringy bark branches, Adam has gathered some paper and dried leaves. A hose coils on the ground and Ruy, Adam and I are standing around a circle of bricks that surround a cone shape that’s been dug into the ground. The sides travel down at a 45-degree angle, Its vertex, a focal point, is more than a meter down from our feet. The walls have been lined with the clay that was dug out of the ground when the hole was made and mixed with cement. The shape is recognisably an upside-down fire.
“what is fire?”, I ask the internet. From my interpretation, a novice understanding goes like this: the fire that I learnt to build as a kid in the backyard used wood, leaves and paper, in other words cellulose. Cellulose is the chemical arrangement of carbon, hydrogen and oxygen. The breaking of chemical bonds rearranges those elements, combines with oxygen in the air and turns it into carbon dioxide and water vapour (hydrogen and oxygen). The breaking and rearranging of chemical bonds both requires and produces heat. As chemical bonds are broken, heat and light are produced, and the heat breaks more chemical bonds and produces more heat. And on and on it cycles.
How was my fire upside down? It’s the heat that starts to break down chemical bonds. So, when I lit the fire at the bottom, the paper was producing heat, heating up the sticks at the top and as they heat up, volatile, combustible gases in the form of hydrocarbons are being released and some are burnt but much is wasted and enters the atmosphere. In an efficient fire, the hydrocarbons are used as fuel rather than released into the atmosphere as greenhouse gases. When a fire is lit at the top, the process heats up the wood underneath and the hydrocarbons that are released can be burnt and converted mostly into carbon dioxide and water vapour.
A few sticks are thrown into the bottom of the pit and paper and leaves are thrown in on top of that. Ruy lights up some paper and the process begins. More sticks are thrown on top and we start circling the pit. Ruy explains that from here on, we will be looking for white spots that appear on the black sticks as they burn. The white spots are where the charred wood is turning to ash. As the cellulose of the wood is converted into hydrocarbons the wood becomes more porous. When the oxygen gets into those pores, the combustion process begins to turn the charcoal into ash. We don’t want ash because we are trying to keep as much carbon as we can out of the atmosphere and keep it in the soil. When we begin to see any white spots, a layer of fuel is thrown on top. This starves the layer beneath of oxygen. We keep circling, looking for white spots and throwing on sticks.
The heat is building and there is barely any smoke. Has it been half an hour or longer? The flames in the pit have blackened and they are swirling around and back into the centre of the flames. The conical shape of the Kon Tiki kiln has created a vortex airflow that draws emissions back into the centre of the fire. The Kon Tiki kiln’s rudimentary and cheap construction belies its efficacy, creating a cleaner and lower emission burn. The heat now is intense, and we are all standing more than a meter away from the circle. At this point, if we were making biochar for sustainable soils, we would throw in manure, urine or food waste to cool the fire down and the minerals would bind to the char in the heat. The process would start again; watch for white spots, throw in more wood, starve the layer underneath of oxygen until the fire builds up and throw some sort of nutrient rich feedstock on the top.
Today though, we are just experimenting with charcoal for drawing. Ruy puts the fire out with water and Adam digs it out with a shovel onto the top of an old water tank. The pieces are mostly too small for drawing. We can still use it for the biochar workshop in June at The Living Classroom, but it’s not a process I would use to make charcoal for drawing. However, by the end of this process I’m ecstatically convinced by the Kon Tiki’s ability to make biochar. Mostly because it’s burning the wood efficiently and releasing less greenhouse gases than a normal outdoor fire, retaining about 50% of carbon in the char. I’m looking forward to making one in my backyard and inviting friends over for a backyard bonfire. The best bit is that I’ll infuse the biochar with manure and my newly planted fruit trees are going to love me for it.
When Adam and Ruy are making biochar in different parts of the world, the cellulose comes from whatever agricultural residues that are available to that community. It’s usually not called cellulose when biochar is made, rather it’s called biomass and could come from coconut husks, wheat or rice chaff, anything that would otherwise get burnt off anyway. When Ruy and Adam travel the world to talk about biochar, their emphasis is on its sustainable and ethical use and production. The main objective of Biochar 4 Sustainable Soils is to demonstrate and promote the adoption of sustainable land management practices involving biochar by using agricultural residues for biochar production and improving crop yields.
In Kandos, slow combustion fires in the house are pretty normal, and once a year there will be a friend or two who will have a party with a bonfire in the dead cold of winter. A mesmerising occasion. When it’s our turn to have a bonfire in the backyard this year, I’m going to experiment with making biochar for my struggling fruit trees. The variables that go into making biochar are mainly the type of biomass feedstock, the temperature and length of time taken for the burn, and the nutrients and minerals that you add to the char either while it is produced or afterward. The variables on the other side of the process is what does my soil need? What food crops am I trying to grow? But most importantly, will my friends turn up and is it polite to ask them to bring chicken poop to the party?