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 feels 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
1. Can we Prevent it? Not really unless we stop drinking coffee altogether, which is not likely to happen. Chaff though, exists on the bean and unless we can genetically modify a coffee bean (which we wouldn’t want to do) then it is likely to stay
2. Can we Reduce? Of course, only roasting in mico-lots, on demand, is the way forward. Batch processing as oppose to continuous operations in our eyes is the best solution given that continuous operations, by its very nature, produces waste.
3. Can we Re-use? No, we cannot reuse the chaff; it needs to be separated from the coffee.
4. Can we Recycle? Yes, we can use this as other products such as bedding for chickens or domestic pets.
5. Can we Recover? Yes, we can use this as compost
6. Disposal? – The final option, and one that we do not consider, all disposal ultimately ends up in the landfill, so don’t go there
7. There are some already very well established methods to deal with the waste chaff, and I dont mean to go over old ground, but two of them are listed below.
Common uses for coffee chaff
Composting:
The firm favourite, and one that we regularly use ourselves.
With composting, as the matter is organic, light and airy, it is ideal for the garden compost bin. All organic matter will want to oxidise and return back to its natural state, and in a compost bin, in the right conditions, this process will be accelerated. In the case of the simple chaff, well this will turn back into its main elements, adding so much more needed nutrients to your blend of composting agents.
Mulching
Not one that we use, but many others we know do. By adding a layer of coffee Chaff to your soil surface it conserves moisture and improves the general health and aesthetics of the soil.
And So…..
We did however, want to see what else we can do with Chaff as the options appear to be a little bit limited, or at least not very well documented.
Our experiment: turning chaff into fuel
Aim
Our Aim in all of this is to create our own waste to energy fuel using the Chaff that we create, and to see what the effects are on that fuel.
The set up that we were using is an a German Manufactured Ruf Briquetter, it has a 155 Tonne Ram and uses a modest 260Barg to compress those briquettes. The machine has been modified this slightly by adding a screw conveyor which can be used to load up the Briquetter whilst in operation, making it much less labour intensive and more of a continuous operation. Bob had also installed an LEV (Local Exhaust Ventilation).
Method
1. Over the course of a 6 week period, we collected our Chaff, and as we are a micro roaster, we do not produce masses of this stuff, so this was a small scale test only (for now)
2. From my cyclone separator I collected approximately 0.5kg of the chaff in a black bin bag.
3. To make this Chaff into a fuel, then it is important that the moisture content is no greater than 14%, which could be tricky, chaff when it is blown during the coffee roasting process, in my experience, picks up moisture and oils from the coffee beans. The moisture we measured was only 12.8%.
4. The Chaff was dropped into the IBC where the screw instantly took it and conveyed it to the briquette drum.
5. The drum in the briquetting machine there was approximately 0.5m2 of sawdust, and a fraction of Chaff.
6. The first few briquettes that were produced were made from 100% sawdust, and after the first half dozen were produced, we started to see how the Chaff affects the nature of the brick, and the whole general appearance.
7. We found that the bricks themselves had a more slick and glazed look, there was less of the dust that would normally be produced. The speckles of chaff were clearly visible (see photographs) and it would appear that the oils may have complemented the sawdust and have acted in some way as a bonding agent (in addition to the 260 Barg pressure of course)
8. Now this is the salient point – the briquettes had a great and very pleasant aroma of coffee. The aroma was quite nutty and was clearly noticeable above the sweet smell of pine – and they burned terrific.
9. So calling all Wasters and Haters of Chaff… send it to North Yorkshire where Bob will blend it and produce this waste into a very useable energy source to keep him warm in the winter
What we learned
- Coffee chaff can be successfully used as a fuel additive
- Moisture content is key (≤14%)
- Blending ratios matter — 100% chaff is probably unrealistic (for now)
- The oils present in chaff may actively improve briquette quality
Could this scale up? We believe so — but it would require further testing, particularly around ratios and consistency.
What’s next
Bob is a local stonemason in East Rounton who has an excellent set up put together to reduce his Carbon Footprint. His briquettes are available locally and may be available one day with that sweet coffee aroma as standard!!
No Diagram
Note from 20th May 2015 – This post seems to have generated quite a bit of interest, and it is worth giving an update on some developments. We recently began some work with York University and Waste Valor, a company set up to find economic value in food waste. The briquettes underwent some testing and the results were encouraging. We are now looking to develop this further, so keep posted for any news.