High carbon content has become the default badge of quality for biochar in networking events. It’s a simple, marketable number that promises stability and sequestration. But it tells you almost nothing about what that biochar will actually do in a specific application. For an industry built on performance, relying on a single metric is a critical oversight.
The discourse around biochar quality must be led by a deeper understanding of its fundamental complexity, moving beyond a single number and toward a profile of specific, functional properties.
Safety is Non-Negotiable
This isn’t about ignoring the fundamentals. Certifying bodies like the European Biochar Certificate (EBC) provide an essential service by setting critical thresholds for contaminants like heavy metals and Polycyclic Aromatic Hydrocarbons (PAHs). They ensure the biochar we use is safe. This is the absolute, non-negotiable baseline for every product.
The real issue though is one of performance. A biochar can be perfectly safe but functionally useless for your specific goal.
The Architects of Biochar: Feedstock and Temperature
A biochar’s performance is dictated by its physical and chemical properties. These are not accidental. They are engineered through the deliberate choice of two main levers: the starting material (feedstock) and the production process (primarily temperature).
Feedstock lays the foundation. A biochar’s inherent mineral composition is a direct legacy of what it was made from:
- Woody materials produce a biochar with lower ash content (<5%) and a higher proportion of fixed carbon.
- Crop residues result in higher ash (5-20%) and bring more nutrients like potassium and calcium to the final product.
- Manures and biosolids yield biochar with the highest concentration of minerals, nitrogen, and phosphorus.
The production temperature then acts as the finishing tool, refining the molecular structure and surface chemistry of that initial material:
- Low Temperature (350-550°C): This process retains more of the feedstock’s original nutrients and creates a surface rich in oxygen-based functional groups. These chemical “hooks” are what generate high Cation Exchange Capacity (CEC), making the biochar a magnet for nutrients and water—the ideal choice for most agricultural applications.
- Medium Temperature (550-750°C): This is the sweet spot for creating a balanced pore structure and reactive surface. It’s perfect for remediation, where the biochar must trap organic pollutants in its pores while its surface chemistry binds and immobilizes heavy metals.
- High Temperature (>750°C): At this temperature, the development of turbostratic crystalline structures, which are similar to graphite, occurs. Most functional groups are stripped away, leaving a carbon-dense, highly stable structure. When you start with a high-carbon feedstock like hardwood, this process creates the perfect biochar for long-term, reliable carbon sequestration.
Using the Right Tool for the Job
Consider a site contaminated with petroleum and heavy metals. To create the right tool for this job, you would start with a low-ash feedstock like waste wood to generate a clean pore structure, then process it at a medium temperature. This specific combination yields a biochar with the micropores needed to trap petroleum and the essential surface chemistry to bind the heavy metals. A high-carbon, high-temperature biochar, regardless of feedstock, would simply be the wrong tool. Then again, I wouldn’t recommend remediation with just biochar. Depending on the contamination type, pairing biochar with microbial consortium would be the better method for remediation.
Adopting an Intelligent Blueprint for Quality
The path forward requires the market to adopt a more intelligent blueprint for quality, a move already being championed by leading certification bodies. The European Biochar Certificate (EBC), for example, has established a framework that moves beyond a single quality score and toward application-specific guidelines for soil and other materials like the EBC-AgroOrganic, EBC-Feed, EBC-ConsumerMaterials, and more.
However, the broader market conversation often lags behind this nuanced approach, still defaulting to a simplistic focus on high carbon content. To unlock biochar’s full potential, producers and buyers alike must embrace the sophistication that these standards offer. The industry needs to shift from asking for a generic “quality score” to demanding a detailed “spec sheet” that guarantees fitness for a particular job.
This means demanding products certified not just for safety, but for performance in a specific role. Following the lead of the EBC, the market should be able to clearly differentiate between products such as:
- Agricultural-Grade: Certified for safety and valued for properties that support farming. This would mean it is likely derived from nutrient-bearing feedstocks and processed at lower temperatures to maximize Cation Exchange Capacity (>15 cmol/kg).
- Remediation-Grade: Certified for safety and engineered from specific feedstocks and temperatures. The goal is to achieve a target surface area (300-400 m²/g) and pore structure for contaminant capture.
- Sequestration-Grade: Certified for safety and valued for its extreme stability. This is the result of combining high-carbon feedstocks with high-temperature processing to achieve a low H:C ratio (<0.2)
The Bottom Line
Carbon sequestration is a vital function, but it’s an outcome of putting a safe and stable material into the soil. Soil science and materials science must lead the conversation.
So when someone tells you their biochar is “high carbon,” you know what it means: it’s stable. That’s a great start. But it’s just that—a start. To get real value, we have to look deeper. We must stop asking just about quantity and start asking about capabilities, a result of the intricate choreography between feedstock and fire.
The most important question is not “How much carbon does it have?” but “What does this biochar do?”
(Yuventius Nicky )
