Cocoa pod husk and the husk left from threshing coffee are different residues, and each has its own point to check before putting it to use. For cocoa pod husk, in a laboratory study, much of the potassium washed out once the husk was already decomposing; and in a study in Trinidad, with a cultivar that accumulates a lot of cadmium, most of the cadmium in the fruit was in the husk. Since heavy metals stay in the biochar during pyrolysis, it is worth testing the husk for cadmium before pyrolysing it. For coffee husk, a sample from Sucumbíos had 7.1% ash on a wet basis and, burned on its own as pellets, gave carbon monoxide far above the reference limit used. The author of that report (now Nina Energy's CSO) concludes that combustion would not be the most convenient route, and that the most appropriate would be to pyrolyse it to produce heat for drying and biochar.
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How much cocoa there is in Ecuador
For 2023, the Ministry of Agriculture and Livestock estimated cocoa production of 379,584 tonnes on 516,629 harvested hectares, based on INEC data. The provinces with the most production were Los Ríos, Manabí, Esmeraldas and Guayas.
We did not find an official source stating how much pod husk comes from that production, nor an official figure for coffee husk, so we do not give those figures. What counts for the decision is the volume at your own farm, collection centre or plant.
Cocoa pod husk and its nutrients
A study published in 2021 measured in the laboratory what happens to the nutrients in cocoa pod husk. Incubated at 20 °C, at 100% relative humidity and in the dark, the husk lost 24% of its dry matter after 14 days and 32% after 30 days.
The figure that stands out is for potassium. In flooded beakers, 11% of the potassium in fresh husk washed out within 48 hours, compared with 92% from partially decomposed husk. Under simulated rain, 33% of the potassium was lost in 25 days, more than for the other nutrients and with more variation; that leaching depended mainly on how often it rained.
The authors themselves warn that the artificial conditions of their experiments limit how far those rates can be extrapolated to farms.
Cadmium: what to check before pyrolysing cocoa pod husk
A study published in 2022 measured where cadmium accumulates in the cocoa fruit. It was done in Trinidad, with a high cadmium-accumulating cultivar (three trees). On average, the pod husk had 2.76 mg of cadmium per kg and the bean (nib) 2.05 mg/kg. According to the authors, most of the cadmium in the fruit was in the pod husk.
We have no data on cadmium in cocoa pod husk from Ecuador, so we do not know how much the husk from your area would have. What matters for biochar is something else: according to the European Biochar Certificate (EBC), biomass loses more than half its weight in pyrolysis, but heavy metals stay, except for some volatile ones such as mercury. That is why biochar has more heavy metals than the biomass it came from.
The EBC sets a cadmium limit for biochar: 1.5 g per tonne of dry matter in its EBC-Agro, EBC-Urban and EBC-Materials classes, and 0.7 g/t in EBC-AgroOrganic; the EBC-Basic class only requires it to be declared. It also notes that values above the limits mainly indicate that the biomass was contaminated. Note: the Trinidad figure is for the husk and the EBC figure is for the biochar; they cannot be compared directly.
Our recommendation: before pyrolysing cocoa pod husk, test it for cadmium, and then test the biochar too.
Coffee husk: ash and combustion
Coffee husk, the residue from threshing, has been tested as a fuel. A 2022 technical report for the NGO CEFA analysed a sample of coffee husk from a collection centre in Sucumbíos. Disclosure: the author of that report, Mario Heredia, is now Chief Scientific Officer (CSO) of Nina Energy, and the report is grey literature, not a peer-reviewed article.
The sample had 7.1% ash on a wet basis; the European Union reference pellet used in the report, 0.3%. In a fixed-bed burner with a vertical flame, coffee husk pellets burned on their own gave 91,412.5 mg/Nm³ of carbon monoxide, corrected to 11% oxygen. A 4:1 mix by volume of coffee husk and palm kernel shell gave 11,276.6 mg/Nm³. The European reference limit used in the report is 500 mg/Nm³: with pellets alone, the measured value was about 180 times that limit, and with the mix, about 23 times (our calculation).
Why ash decides which burner works is explained in our Spanish-language article El problema de la ceniza.
Pyrolysing the husk
The report concludes that combustion would not be the most convenient route to add value to coffee husk, and that the most appropriate would be pyrolysis processes that produce heat for drying and biochar. This is the conclusion of one report, with one sample; it is not proof that any pyrolysis of coffee husk will work.
If you want the biochar certified under the EBC, the same rules apply as to any other, including: an H/Corg ratio below 0.7 in all its classes, and pyrolysis gases that are recovered or burned, not released into the atmosphere. The certificate class shows which use the biochar is admissible for. And if it is for farming in Ecuador, Agrocalidad requires registration to sell fertilisers, soil amendments and related agricultural products; check with Agrocalidad whether your product falls into that category. What to check before buying or selling biochar is covered in Biochar in Ecuador: what it is, what it is used for and how to tell whether it is good quality.
Questions for any supplier (us included)
· How many tonnes of husk come out each month, and at what moisture?
· Is the husk left in the field today? What nutrients does my soil need?
· If it is cocoa pod husk: do I have a cadmium analysis of it? Will you give me the cadmium analysis of the biochar?
· If it is coffee husk: how much ash does mine have? Is the equipment designed for that ash?
· What happens to the pyrolysis gases?
· Who buys the biochar, and for what use? Which EBC class does that use require?
· Can you show me an analysis of my own husk, not of a husk from the literature?
Frequently asked questions
Does leaving cocoa pod husk in the field return its nutrients?
The study we cite did not measure this on farms. In the laboratory, partially decomposed husk lost 92% of its potassium in 48 hours under flooding. The authors warn that those rates cannot simply be extrapolated to farms.
Does cocoa pod husk contain cadmium?
In the Trinidad study we cite, with a high-accumulating cultivar, most of the cadmium in the fruit was in the husk. We have no data from Ecuador: the only way to know for your husk is to test it.
Can coffee husk be burned?
It burns, but in the report we cite, burned alone as pellets it gave about 180 times the reference limit for carbon monoxide (our calculation). Its author (now Nina Energy's CSO) concludes that pyrolysis would be a more appropriate route.
Can cocoa pod husk biochar be certified?
It depends on its analyses. If you want EBC certification, the biochar must meet, among other things, the H/Corg below 0.7 and the cadmium limit of the class you apply for (the EBC-Basic class only requires it to be declared).
Conclusion
For cocoa or coffee husk to go from waste to resource, we recommend measuring first. For cocoa pod husk, cadmium, because in pyrolysis it stays in the biochar. For coffee husk, ash: in the sample we cite it was 7.1% on a wet basis, compared with 0.3% for the reference pellet. Start with an analysis of your own husk.
Sources and methodology
Ecuador data:
· Ministerio de Agricultura y Ganadería (MAG), Estado del cultivo de cacao en el Ecuador 2023, based on INEC-ESPAC 2023 data; production estimated from harvested area and target yields; figures updated to June 2024. PDF (accessed 27 Oct 2026)
Studies:
· Hougni, D. G., Schut, A. G. T., Woittiez, L. S., Vanlauwe, B. and Giller, K. E. (2021). How nutrient rich are decaying cocoa pod husks? The kinetics of nutrient leaching. Plant and Soil 463: 155–170. Article (accessed 27 Oct 2026)· Blommaert, H., Aucour, A.-M., Wiggenhauser, M., Moens, C., Telouk, P., Campillo, S., Beauchêne, J., Landrot, G., Testemale, D., Pin, S., Lewis, C., Umaharan, P., Smolders, E. and Sarret, G. (2022). From soil to cacao bean: Unravelling the pathways of cadmium translocation in a high Cd accumulating cultivar of Theobroma cacao L. Frontiers in Plant Science 13: 1055912. Article (accessed 27 Oct 2026)· Heredia, M. A. (2022). Sistematización: resultados e impactos del uso de generadores de calor que utilizan biomasa residual. Technical report for the Comité Europeo para la Formación y la Agricultura (CEFA), Quito, 12 Jun 2022. Grey literature; the author is Chief Scientific Officer (CSO) of Nina Energy. p. 8, Tables 7 and 8, and p. 28. (Not published online; read on 27 Oct 2026)
Standards:
· European Biochar Certificate (EBC), v10.5E, 14 Aug 2025 — ch. 3, §7.2, §7.5 and §8.3. PDF (accessed 21 Oct 2026)· Agrocalidad, Manual técnico para el registro y control de fertilizantes, enmiendas de suelo y productos afines de uso agrícola, edition 7 (approved 13 Jun 2022); current validity not confirmed — §5.1. PDF (accessed 21 Oct 2026)
Methodology: every figure comes from the original text of the source, except the calculations marked as ours. The nutrient study is laboratory-scale, the cadmium study is from Trinidad with a single cultivar, and the coffee husk data come from a technical report with one sample; their figures are not predictions for your husk. This article does not report data on Nina Energy's biochar or equipment.
