What is biochar?

Biochar is what you get when you heat dry biomass, in our case coffee pruning residue, husk, parchment, or pulp, in a low-oxygen environment. The biomass does not combust. The volatile compounds are driven off and burned cleanly above the chamber, while the solid carbon left behind transforms into a porous material that stays stable in soil for centuries.

It looks like granulated charcoal. It is not charcoal. Charcoal is fuel, designed to burn. Biochar is the opposite. It is designed to stay put.

In a normal fire, biomass and oxygen become CO₂, water, and ash. All the carbon goes back to the atmosphere.

In pyrolysis, biomass and heat without oxygen produce solid carbon and a stream of gases. About a quarter of the original mass survives as biochar. The gases are burned cleanly above the chamber, and that flame keeps the reaction going. No external fuel is needed once the kiln is up to temperature.

Not all the carbon in biochar is created equal. The certification body splits every certified biochar into two parts.

Most of the carbon (around three quarters) is the long-lived fraction. It persists in soil for over a thousand years and is what gets sold as a durable carbon removal credit.

The remaining quarter is shorter-lived. It decays over a window of decades. It cannot be sold as removal, but it can be used to compensate the methane emitted during pyrolysis.

The reason we trust biochar to last is that we can already observe it. The Amazon basin contains pockets of Terra Preta, dark soils up to two meters thick, dating back hundreds to thousands of years. Indigenous Amazonian communities created them by mixing charred biomass into otherwise nutrient-poor tropical soils.

Those soils still contain the original biochar carbon today, and they still outperform surrounding soils on fertility, microbial activity, and water holding. They are also still farmed.

Biochar is not a new climate technology. It is an ancient agricultural practice that turns out to also sequester carbon at scales that matter to atmospheric chemistry.

Three things, mostly.

It holds water. Biochar is extraordinarily porous and acts as a sponge in the root zone. In drought conditions, that can be the difference between a survivable harvest and a write-off.

It hosts microbes and binds nutrients. The porosity that holds water also hosts microbial communities and adsorbs nutrients before they leach away. Once charged with compost or fertilizer, biochar becomes a slow-release nutrient platform.

It buffers pH. Most biochars are mildly alkaline, which counteracts the acidification that intensive coffee cultivation causes over decades.

It is not fertilizer. Raw biochar applied to soil with nothing else can actually depress yield in the first season as it adsorbs nutrients before plants can reach them. This is why charging the biochar with compost or fertilizer before field application is the standard practice.

It is not a free climate fix. It is a real, well-understood contribution to durable carbon removal with strong agronomic co-benefits. Its value in coffee is that the carbon is an easy second-order justification for an investment that already pencils out on agronomy alone.

It is not the same product everywhere. Feedstock matters. Biochar from coffee pruning behaves differently than biochar from rice husks or pulp. The MRV process tracks feedstock for this reason.