Foundational
Coffee waste and by-products
What the husk, pulp, mucilage, parchment, silverskin and spent grounds are, where each arises, and which uses for them are established or only proposed.
In short
A cup of coffee uses a small part of the fruit it came from. The skin and pulp, the sticky layer under them, the papery parchment, the thin silverskin and finally the wet grounds are all left over at one stage or another. One review puts the discarded share at approximately 90 per cent of the edible parts of the cherry.
A great deal has been written about what could be done with these. This page separates what each one is, which is settled, from what has been proposed for it, which mostly is not.
Where each by-product comes off
Sourced
The order in which the layers are removed, following a review of coffee by-products. Which of the first three arise, and in what form, depends on how the coffee is processed.
Husk, or cascara
The dried skin and pulp of the cherry. In the dry method the whole fruit is dried and the husk comes off in one piece; the review says it makes up nearly 45 per cent of the cherry.
Pulp and mucilagenot always done
In wet processing the skin and pulp are removed fresh and the sticky mucilage is then fermented or scrubbed away. The review cites figures for Colombia of 39 kg of skin and pulp and 22 kg of mucilage from 100 kg of fresh cherries.
Parchment
The stiff husk around the dried bean, removed by hulling machinery at the dry mill before export.
Silverskin
A thin skin clinging to the green bean that comes away during roasting, where roasters know it as chaff.
Spent grounds
What is left in the filter or the basket after brewing: the last by-product, and the only one made in kitchens and cafés.
A model of where each by-product arises. The quantities are one review's citations of earlier studies and were not checked against those studies.
Eating and drinking them is a legal question first
Sourced
The review is plain that the main consideration for using coffee by-products as food is their regulatory status. In the European Union a food is treated as novel if it was not regularly consumed there before 15 May 1997, and a novel food needs authorisation, supported by analysis of toxic substances and toxicological studies, before it may be sold.
Dried coffee cherry pulp, the material sold as cascara, has been through that process: its status in the European Union is set out on the cascara page, from the regulation itself. For the other by-products this page states no status, because none was read.
The review lists what would need to be analysed to make by-products safe as ingredients for the general population: pesticides, mycotoxins, acrylamide and gluten. It also notes that they contain caffeine, at levels below those of green and roasted beans.
Spent grounds: what is proposed for them
Sourced
- What they are
- A 2025 review describes spent grounds as mostly dietary fibre, close to half by composition, with protein, oil, minerals and some remaining caffeine and chlorogenic acids. Brewing takes out the soluble part and leaves this.
- On soil
- The review reports that grounds have been found to improve soil structure, aeration and fertility. That is a citation of earlier work; no trial was read, and how much to use, composted or not, is not something this page can say.
- As fuel
- The oil can be extracted with a solvent and converted to biodiesel; the review cites one laboratory study reporting a high conversion yield. Grounds can also be turned by heating into a bio-oil or a carbon-rich char. These are demonstrated in the laboratory, which is not the same as being done at scale.
- In food and packaging
- The review covers grounds added to baked goods and fermented drinks and used in packaging materials. It says that no safety issue has been reported so far, which it puts down to how little grounds are yet used in food, and cites one study that found acrylamide in grounds well below safety thresholds. It ends by saying future work must address safety concerns, naming acrylamide formation and heavy metal contamination.
Reused does not mean better, without the sums
CoffeeHQ explanation
It is tempting to treat any use of a waste as a gain. Whether it is depends on what the use displaces and what it costs: extracting oil from grounds takes a solvent and energy, drying wet pulp takes heat, and collecting small amounts from many places takes transport. None of the reviews read here weighs those against the alternative, and neither does this page.
What can be said is narrower. Wet processing produces wastewater rich in organic matter, and that is a measured problem with documented remedies, described in the processing guides. For the rest, a claim that a product made from coffee waste is sustainable is a claim, and worth the same scrutiny as any other.
The grounds in your own kitchen
CoffeeHQ explanation
Ordinary practice, not advice drawn from a study.
- Composting is the unremarkable option. Grounds and paper filters go into a compost heap or a food-waste collection like other kitchen scraps. Follow your local collection's rules on what it accepts.
- Be modest about the garden. Grounds are often recommended straight onto soil or around plants. No trial of that was read, so this page gives no amount and makes no promise about pests or acidity.
- Do not put them down the sink. Wet grounds settle and can block pipes, which is a plumbing matter and the one piece of advice here that needs no study.
What is not claimed for any by-product
CoffeeHQ explanation
No health benefit is claimed for any by-product. The reviews report many laboratory and animal findings and this page uses none of them. It gives no figure for how much coffee waste the world produces, no recommendation to eat or drink anything, and no recipe. It does not say that silverskin, parchment or mucilage may lawfully be sold as food anywhere. And it does not say that any reuse described is carried out at commercial scale, because nothing read establishes that.
What to do next
- Cascara — The one by-product with a settled food status in the European Union, and what the regulation says.
- How coffee is processed — Where pulp, mucilage and parchment come off, process by process.
- Fermentation — What happens to the mucilage before it is washed away.
- Sustainability claims — How to read a claim that something is made from waste.