It is the outer skin of coffee beans! A by-product of roasting.
Great uses for coffee chaff:
Coffee bean chaff adds extremely helpful nutrients, the main component of which is nitrogen, to compound and mulch mixtures. Perfect for adding to your garden beds and composts!
If you have feathery and furry friends, such as chickens and rabbits, you can use coffee chaff as an alternative to their beddings. It is especially great for chickens because these feathery fellows need something to scratch and giving them loads of chaff for this purpose will make them super happy. Because it is light, coffee chaff is also easy to handle and pick up. If your chickens poop in their coop, the chaff will form clumps in the littered area.