Coffee Chaff: What It Is, Why It’s in Your Coffee and How to Use It

Coffee chaff is the thin, papery skin that comes off coffee beans during roasting. It is the silverskin, a fine membrane that clings to the green coffee bean. As the beans heat, dry out and expand, it loosens and flakes away as light, golden-brown flakes that roasters collect and usually throw out. A little chaff often stays trapped in the crease of the bean, which is why you may see pale flecks in freshly ground coffee. It is harmless to drink. The chaff that roasters collect can be composted, used as a garden soil amendment or animal bedding, or even turned into fuel and car parts.

Where Chaff Comes From

A coffee cherry has several layers around the seed: the skin and fruit pulp, a sticky mucilage, a tougher papery shell called parchment, and finally the silverskin, which hugs the bean itself. The skin, pulp and parchment are removed at the farm and dry mill, but much of the silverskin stays on the green coffee that roasters buy. Our guide to coffee bean anatomy shows each layer.

During roasting, the bean loses moisture and swells, and the silverskin dries, cracks and lifts away. Roasting machines blow it out of the drum with the exhaust air into a chaff collector. It is not the same as the coffee cherry husk used to make cascara tea, which comes from the outer fruit.

Chaff in Ground Coffee: Is It Bad?

No. If you see pale or white flecks when you grind coffee, it is almost always chaff trapped in the crease down the center of the bean. It is safe to drink and in small amounts has little effect on flavor. You will see more of it in light roasts, which do not get hot enough for long enough to shed all of it, and less in dark roasts. Roast levels explains the difference.

Some people remove it for a cleaner cup, especially in light-roast pour-over, where large amounts can add a slightly papery or dry taste. The easiest ways are to gently blow across the freshly ground coffee in a bowl, or shake it in a sieve so the lighter flakes rise. Some coffee grinders include a bellows or a chaff-reducing design for the same reason. Chaff also adds a little static, so ground coffee can cling to the grinder.

Chaff and Home Roasting

If you roast at home, chaff is the mess you will notice first. It floats out of popcorn poppers, drum roasters and pans and drifts around the kitchen. Most home roasting machines have a chaff collector or tray. If you roast in a pan or popper, cool the beans by tossing them between two metal colanders outside, or in front of a fan, and the chaff will blow away. Empty the chaff collector after every roast, because chaff is very flammable and is a common cause of roaster fires. See our tips for roasting coffee at home.

Uses for Coffee Chaff

Compost

Composting is the best use for chaff. It contains about 2% nitrogen and a good amount of potassium, with a carbon-to-nitrogen ratio of roughly 19:1, close to what compost microbes like. Because it is so dry and light, mix it with wetter materials such as kitchen scraps or grass clippings, and water it in. Layer it thinly or stir it through rather than adding a thick mat, which can shed water. It also pairs well with spent coffee grounds; see our ideas for using coffee grounds.

Garden Mulch and Soil Amendment

Chaff can be dug into garden beds to add organic matter, or used as a thin mulch mixed with other materials so it does not blow away. Research suggests raw silverskin contains compounds that can slow plant growth in large amounts, and that composting it first, ideally with woody garden waste, removes the problem and makes its nutrients easier for plants to use. So compost it first for vegetable beds and seedlings, and use raw chaff sparingly. It should not be your only fertilizer, since plants can use only a small part of its nitrogen right away.

Animal Bedding

Some backyard chicken keepers and small-animal owners use chaff as bedding because it is soft, absorbent and free from local roasters. It is very light and can be dusty, so mix it with wood shavings or straw, and keep it away from food and water dishes. Used bedding can go straight into the compost.

Fuel and Fire Starter

Dry chaff burns quickly, which makes it a handy fire starter for a fire pit or wood stove. On a larger scale, chaff can be pressed into pellets or briquettes for fuel. The same property makes it a hazard: store bags of chaff away from heat, and never leave it to build up in a roaster.

Industrial Uses

Researchers and manufacturers are testing chaff in bioplastics, packaging and building materials. In 2019, Ford announced it was using coffee chaff from McDonald’s coffee supply in a plastic composite for car headlamp housings, making the parts lighter and using less energy to mold.

How to Get Coffee Chaff

The easiest source is a local coffee roaster. Busy roasteries fill bags of chaff every week and many are happy to give it away to gardeners, farms and community gardens. Call ahead, bring your own bags or bins, and ask when they usually empty the chaff collector. Keep it dry until you use it, since damp chaff can turn moldy and clump.

Reusing chaff is a small but practical way to cut waste from coffee roasting, and for gardeners it is a free source of organic matter that would otherwise go to the landfill.