Coffee Chaff: From Roasting Waste to Renewable Fuel
Coffee chaff is the dried skin, or husk, of the coffee bean. It comes loose during the roasting process and, if you’re a roaster, you’ll know exactly how annoying it can be. It’s light, it gets everywhere, and it can sometimes feel like you’re forever cleaning rather than roasting coffee.
That said, chaff is also a by‑product — and nobody likes waste. Especially waste that could be reused. With landfill always being the least attractive option, we wanted to understand whether coffee chaff could be put to better use.
What is coffee chaff?
Chaff is a natural part of the coffee bean. Unless we stop drinking coffee altogether (which doesn’t feel likely), chaff isn’t going anywhere. It’s present on every bean and separates during roasting as the beans expand and crack.
In other words: chaff is unavoidable — but waste is a choice.
Why we wanted to do better than bin it
- Can we prevent it? Not really — unless we stop drinking coffee altogether. Chaff exists on the bean, and unless we genetically modify coffee (which we wouldn’t want to do), it’s here to stay.
- Can we reduce it? To an extent. Roasting in micro‑lots and on demand helps. Batch processing, rather than continuous operations, produces less waste overall.
- Can we reuse it? No — chaff must be separated from the coffee.
- Can we recycle it? Yes — it can be used as bedding for chickens or domestic pets.
- Can we recover it? Yes — composting is a viable option.
- Disposal? The final option, and one we try to avoid. Disposal ultimately means landfill.
Common uses for coffee chaff
Composting
The firm favourite, and one that we regularly use ourselves.
As an organic, light, and airy material, chaff is ideal for composting. Under the right conditions, it breaks down quickly and returns valuable nutrients to the soil.
Mulching
Not one that we personally use, but many others do. When layered onto soil, chaff can help conserve moisture and improve the overall health of garden beds.
That said, we still wanted to see what else could be done — because the options felt limited and poorly documented.
Our experiment: turning chaff into fuel
Aim
Our aim was to see whether we could convert our coffee chaff into a usable waste‑to‑energy fuel and understand how it behaves in that form.
The setup used a German‑manufactured RUF briquetter with a 155‑tonne ram operating at 260 bar. The machine was modified with a screw conveyor for continuous loading and fitted with local exhaust ventilation.
Method
- Over six weeks, we collected our coffee chaff. As a micro‑roaster, volumes were relatively small — this was a small‑scale test.
- From the cyclone separator, we collected around 0.5 kg of chaff.
- Moisture content needed to be below 14%. Chaff can absorb oils and moisture from roasted beans, but ours measured 12.8%.
- The chaff was dropped into an IBC, where the screw conveyor transported it into the briquette chamber.
- The drum contained approximately 0.5 m² of sawdust, with a small proportion of chaff added.
- Initial briquettes were 100% sawdust. After several runs, chaff influence became visible.
- The briquettes developed a smoother, glazed finish with visible chaff speckles. Oils in the chaff appeared to act as a natural bonding agent.
- The final and most surprising result — the briquettes smelled unexpectedly good, with a nutty coffee aroma, and burned extremely well.
What we learned
- Coffee chaff can successfully be used as a fuel additive
- Moisture content is critical (≤14%)
- Blending ratios matter — 100% chaff is unlikely to work alone
- Oils in chaff may improve briquette structure and binding
Could this scale? Potentially — though further testing around ratios and consistency would be required.
What’s next
Bob, a local stonemason in East Rounton, has since developed an excellent low‑carbon setup using briquettes like these. His work has sparked wider interest, including collaboration with York University and Waste Valor to explore the commercial potential of food‑waste fuels.
We’ll share more as this develops.